Let us next consider the various techniques for microstructural examination.
It is usually necessary to prepare a section of a material in order to study the
size, shape and distribution of crystals within it. In the case of metallic
materials, this is referred to as metallographic examination (‘materialography’
is sometimes used more generally), and great precautions have to be taken at
every stage to ensure that the method of preparation does not itself alter the
microstructure originally present.
If the section for study is cut from the bulk by milling or sawing, or by the
use of an abrasive cutting wheel, ample cooling and lubrication has to be
provided to prevent its temperature from rising. Gross distortions from the
cutting process are eliminated by grinding the surface with successively
finer abrasives such as emery or silicon carbide. If the grains are coarse
enough to be seen with the naked eye, one can at this stage prepare the
surface for macroscopic examination.
The surface of the specimen is etched, usually in a dilute acid, by immersing
it or swabbing it until the individual grains are revealed. Because of the
different rates of chemical attack along different planes in a crystal, when
the surface is etched, crystallographic terraces are formed upon each grain
and these reflect light in directions which vary with the orientation of the
grain, so that some crystals appear light and some dark. The macrostructure
of a piece of cast metal which has been prepared in this way
A much lighter etching treatment is applied for microscopical examination
than for macro-studies. With some etching reagents and very short etching
times, metal is dissolved only at the grain boundaries, giving rise to shallow
grooves there, which are seen as a network of dark lines under the microscope.
A reflecting optical microscope may give magnifications of over 1000 ×,
with a resolution of about 1 ìm. The upper limit of magnification of the
optical microscope is often inadequate to resolve structural features which
are important in engineering materials, however, and electron microscopy is
widely employed for this purpose. Field-ion microscopy is a research tool
with a resolving power that permits the resolution of the individual atoms in
crystals and these can be identified by use of the atom-probe technique.
Saturday, May 2, 2009
Crystal structure
Crystal structure refers to the ordering of atoms into different crystalline
arrangements. It is the arrangement of these atoms – the strength and
directionality of the interatomic bonds – which determines the ultimate strength
of the solid. Techniques involving X-ray or electron diffraction are employed
to determine crystal structures, and four types of interatomic bonding are
recognized: van der Waals, covalent, ionic and metallic. The latter three
‘primary’ bonds are limiting cases, however, and a whole range of intermediate
bonding situations also exist in solids.
The van der Waals force is a weak ‘secondary’ bond and it arises as a
result of fluctuating charges in an atom. There will be additional forces if
atoms or molecules have permanent dipoles as a result of the arrangement of
charge inside them. In spite of their low strength, these forces can still be
important in some solids; for example it is an important factor in determining
the structure of many polymeric solids.
Many common polymers consist of long molecular carbon chains with
strong bonds joining the atoms in the chain, but with the relatively weak van
der Waals bonds joining the chains to each other. Polymers with this structure
are thermoplastic, i.e. they soften with increasing temperatures and are readily
deformed, but on cooling they assume their original low-temperature properties
and retain the shape into which they were formed.
The essential feature of a covalent bond is the sharing of electrons between
atoms, enabling them to attain the stable configuration corresponding to a
filled outermost electron shell. Thus, an atom with n electrons in that shell
can bond with only 8 – n neighbours by sharing electrons with them.
For example, when n = 4, as in carbon in the form of diamond, one of the
hardest materials known, each atom is bonded equally to four neighbours at
the corners of a regular tetrahedron and the crystal consists of a covalent molecule.
The elements can be divided into two classes, electronegative elements
(such as oxygen, sulphur and the halogens) that tend to gain a few electrons
to form negatively charged ions with stable electron shells, and electropositive
elements (such as metals) that easily dissociate into positive ions and free
electrons. Ionic bonding consists of an electrostatic attraction between positive
and negative ions. If free atoms of an electropositive element and an
electronegative element are brought together, positive and negative ions will
be formed which will be pulled together by electrostatic interaction until the
electron clouds of the two ions start to overlap, which gives rise to a repulsive
force. The ions thus adopt an equilibrium spacing at a distance apart where
the attractive and repulsive forces just balance each other.
arrangements. It is the arrangement of these atoms – the strength and
directionality of the interatomic bonds – which determines the ultimate strength
of the solid. Techniques involving X-ray or electron diffraction are employed
to determine crystal structures, and four types of interatomic bonding are
recognized: van der Waals, covalent, ionic and metallic. The latter three
‘primary’ bonds are limiting cases, however, and a whole range of intermediate
bonding situations also exist in solids.
The van der Waals force is a weak ‘secondary’ bond and it arises as a
result of fluctuating charges in an atom. There will be additional forces if
atoms or molecules have permanent dipoles as a result of the arrangement of
charge inside them. In spite of their low strength, these forces can still be
important in some solids; for example it is an important factor in determining
the structure of many polymeric solids.
Many common polymers consist of long molecular carbon chains with
strong bonds joining the atoms in the chain, but with the relatively weak van
der Waals bonds joining the chains to each other. Polymers with this structure
are thermoplastic, i.e. they soften with increasing temperatures and are readily
deformed, but on cooling they assume their original low-temperature properties
and retain the shape into which they were formed.
The essential feature of a covalent bond is the sharing of electrons between
atoms, enabling them to attain the stable configuration corresponding to a
filled outermost electron shell. Thus, an atom with n electrons in that shell
can bond with only 8 – n neighbours by sharing electrons with them.
For example, when n = 4, as in carbon in the form of diamond, one of the
hardest materials known, each atom is bonded equally to four neighbours at
the corners of a regular tetrahedron and the crystal consists of a covalent molecule.
The elements can be divided into two classes, electronegative elements
(such as oxygen, sulphur and the halogens) that tend to gain a few electrons
to form negatively charged ions with stable electron shells, and electropositive
elements (such as metals) that easily dissociate into positive ions and free
electrons. Ionic bonding consists of an electrostatic attraction between positive
and negative ions. If free atoms of an electropositive element and an
electronegative element are brought together, positive and negative ions will
be formed which will be pulled together by electrostatic interaction until the
electron clouds of the two ions start to overlap, which gives rise to a repulsive
force. The ions thus adopt an equilibrium spacing at a distance apart where
the attractive and repulsive forces just balance each other.
Evolution of the Microprocessor
The Intel Corporation is generally acknowledged as the company that introduced the
first microprocessor successfully into the marketplace. Its first processor, the 4004, was
introduced in 197 1 and evolved from a development effort while making a calculator chip
set. The 4004 microprocessor was the central component in the chip set, which was called
the MCS-4. The other components in the set were a 4001 ROM, a 4002 RAM, and a 4003
shift register.
Shortly after the 4004 appeared in the commercial marketplace, three other
general-purpose microprocessors were introduced: the Rockwell International 4-bit PPS-4,
the Intel 8-bit 8008, and the National Semiconductor 16-bit IMP-16. Other companies,
such as General Electric, RCA, and Viatron, also made contributions to the development of
the microprocessor prior to 197 1.The microprocessors introduced between 197 1 and 1972 were the first-generation systems designed using PMOS technology. In 1973, second-generation microprocessors such as the Motorola 6800 and the Intel 8080 (8-bit microprocessors) were introduced.The second-generation microprocessors were designed using NMOS technology. This
technology resulted in a significant increase in instruction execution speed over PMOS and
higher chip densities. Since then, microprocessors have been fabricated using a variety of
technologies and design.
NMOS microprocessors such as the Intel 8085, the Zilog 280,
and the Motorola 6800/6809 were introduced based on second-generation microprocessors.
A third generation HMOs microprocessor, introduced in 1978 is typically represented by
the Intel 8086 and the Motorola 68000, which are 16-bit microprocessors.
During the 1980’s, fourth-generation HCMOS and BICMOS (a combination of
bipolar and HCMOS) 32-bit microprocessors evolved. Intel introduced the first commercial
32-bit microprocessor, the problematic Intel 432, which was eventually discontinued.
Since 1985, more 32-bit microprocessors have been introduced. These include Motorola’s
68020, 68030, 68040, 68060, PowerPC, Intel’s 80386, 80486, the Intel Pentium family,
Core Duo, and Core2 Duo microprocessors..
The performance offered by the 32-bit microprocessor is more comparable to
that of superminicomputers such as Digital Equipment Corporation’s VAX11/750 and
VAX11/780. Intel and Motorola also introduced RISC microprocessors: the Intel 80960
and Motorola 88 100/PowerPC, which had simplified instruction sets. Note that the purpose
of RISC microprocessors is to maximize speed by reducing clock cycles per instruction.
Almost all computations can be obtained from a simple instruction set. Note that, in order
to enhance performance significantly, Intel Pentium Pro and other succeeding members of
the Pentium family and Motorola 68060 are designed using a combination of RISC and
CISC.of the Motorola 68XXX and PowerPC microprocessors will
be provided next. Motorola’s 32-bit microprocessors based on the 68000 (16-bit
microprocessor) architecture include the MC68020, MC68030, MC68040, and MC68060.
Table 1.1 compares the basic features of some of these microprocessors with the 68000.
MC68020 is Motorola’s first 32-bit microprocessor. The design of the 68020 is
based on the 68000. The 68020 can perform a normal read or write cycle in 3 clock cycles
without wait states as compared to the 68000, which completes a read or write operation in
4 clock cycles without wait states. As far as the addressing modes are concerned, the 68020
includes new modes beyond those of the 68000. Some of these modes are scaled indexing,
larger displacements, and memory indirection.
first microprocessor successfully into the marketplace. Its first processor, the 4004, was
introduced in 197 1 and evolved from a development effort while making a calculator chip
set. The 4004 microprocessor was the central component in the chip set, which was called
the MCS-4. The other components in the set were a 4001 ROM, a 4002 RAM, and a 4003
shift register.
Shortly after the 4004 appeared in the commercial marketplace, three other
general-purpose microprocessors were introduced: the Rockwell International 4-bit PPS-4,
the Intel 8-bit 8008, and the National Semiconductor 16-bit IMP-16. Other companies,
such as General Electric, RCA, and Viatron, also made contributions to the development of
the microprocessor prior to 197 1.The microprocessors introduced between 197 1 and 1972 were the first-generation systems designed using PMOS technology. In 1973, second-generation microprocessors such as the Motorola 6800 and the Intel 8080 (8-bit microprocessors) were introduced.The second-generation microprocessors were designed using NMOS technology. This
technology resulted in a significant increase in instruction execution speed over PMOS and
higher chip densities. Since then, microprocessors have been fabricated using a variety of
technologies and design.
NMOS microprocessors such as the Intel 8085, the Zilog 280,
and the Motorola 6800/6809 were introduced based on second-generation microprocessors.
A third generation HMOs microprocessor, introduced in 1978 is typically represented by
the Intel 8086 and the Motorola 68000, which are 16-bit microprocessors.
During the 1980’s, fourth-generation HCMOS and BICMOS (a combination of
bipolar and HCMOS) 32-bit microprocessors evolved. Intel introduced the first commercial
32-bit microprocessor, the problematic Intel 432, which was eventually discontinued.
Since 1985, more 32-bit microprocessors have been introduced. These include Motorola’s
68020, 68030, 68040, 68060, PowerPC, Intel’s 80386, 80486, the Intel Pentium family,
Core Duo, and Core2 Duo microprocessors..
The performance offered by the 32-bit microprocessor is more comparable to
that of superminicomputers such as Digital Equipment Corporation’s VAX11/750 and
VAX11/780. Intel and Motorola also introduced RISC microprocessors: the Intel 80960
and Motorola 88 100/PowerPC, which had simplified instruction sets. Note that the purpose
of RISC microprocessors is to maximize speed by reducing clock cycles per instruction.
Almost all computations can be obtained from a simple instruction set. Note that, in order
to enhance performance significantly, Intel Pentium Pro and other succeeding members of
the Pentium family and Motorola 68060 are designed using a combination of RISC and
CISC.of the Motorola 68XXX and PowerPC microprocessors will
be provided next. Motorola’s 32-bit microprocessors based on the 68000 (16-bit
microprocessor) architecture include the MC68020, MC68030, MC68040, and MC68060.
Table 1.1 compares the basic features of some of these microprocessors with the 68000.
MC68020 is Motorola’s first 32-bit microprocessor. The design of the 68020 is
based on the 68000. The 68020 can perform a normal read or write cycle in 3 clock cycles
without wait states as compared to the 68000, which completes a read or write operation in
4 clock cycles without wait states. As far as the addressing modes are concerned, the 68020
includes new modes beyond those of the 68000. Some of these modes are scaled indexing,
larger displacements, and memory indirection.
Features of 32-bit and 64-bit Microprocessors
In this section we describe the basic aspects of typical 32- and 64-bit microprocessors.
Topics include on-chip features such as pipelining, memory management, floating-
point, and cache memory implemented in typical 32- and 64-bit microprocessors. The
first 32-bit microprocessor, Intel’s problematic iAPX432, was introduced in 1980. Soon
afterward, the concept of mainji-ame on a chip or micromainframe was used to indicate the
capabilities of these microprocessors and to distinguish them from previous 8- and 16-bit
microprocessors.
The introduction of several 32-bit microprocessors revolutionized the
microprocessor world. The performance of these 32-bit microprocessors is actually more
comparable to that of superminicomputers such as Digital Equipment Corporation’s
VAXl1/750 and VAX11/780. Designers of 32-bit microprocessors have implemented
many powerful features of these mainframe computers to increase the capabilities of
microprocessor chip sets: pipelining, on-chip cache memory, memory management, and
floating-point arithmetic.In pipelining, instruction fetch and execute cycles overlap. This method allows simultaneous preparation for execution of one or more instructions while another instruction is being executed. Pipelining was used for many years in mainframe and minicomputer CPUs to speed up the instruction execution time of these machines. The 32-bit microprocessors implement the pipelining concept and operate simultaneously on several 32-bit words, which may represent different instructions or part of a single instruction.
Although pipelining greatly increases the rate of execution of nonbranching code,
pipelines must be emptied and refilled each time a branch or jump instruction appears in
the code. This may slow down the processing rate for code with many branches or jumps.
Thus, there is an optimum pipeline depth, which is strongly related to the instruction set,
architecture, and gate density attainable on the processor chip.With memory management, virtual memory techniques, traditionally a feature of mainframes, are also implemented as on-chip hardware on typical 32-bit microprocessors.
This allows programmers to write programs much larger than those that could fit in the
main memory space available to microprocessors; the programs are simply stored on a
secondary device such as a hard disk, and portions of the program are swapped into main
memory as needed.Segmentation circuitry has been included in many 32-bit microprocessor chips.With this technique, blocks of code called segments, which correspond to modules of the
program and have varying sizes set by the programmer or compiler, are swapped. For many
applications, however, an alternative method borrowed from mainframes and superminis
calledpaging is used. Basically, paging differs from segmentation in that pages are of equal
size. Demandpaging, in which the operating system swaps pages automatically as needed,
can be used with all 32-bit microprocessors।
The 64-bit microprocessors such as Power PC 750 include all the features of 32-bit
microprocessors. In addition, they contain multiple on-chip integer and floating-point units
and a larger address and data buses. The 64-bit microprocessors can typically execute four
instructions per clock cycle and can run at a clock speed of over 2 GHz. The original Pentium
microprocessor is a CISC microprocessor. Pentium Pro and other succeeding members of
the Pentium family are designed using a combination of mostly microprogramming (CISC)
and some hardwired control (RISC) whereas the PowerPC is designed using hardwired
control with almost no microcode. The PowerPC is a RISC microprocessorand therefore
includes a simple instruction set. This instruction set includes register-to-register, load, and
store instructions. All instructions involving arithmetic operations use registers; load and
store instructions are utilized to access memory. Almost all computations can be obtained
from these simple instructions. Finally, 64-bit microprocessors are ideal candidates for
data-crunching machines and high-performance desktop systems and workstations.
Topics include on-chip features such as pipelining, memory management, floating-
point, and cache memory implemented in typical 32- and 64-bit microprocessors. The
first 32-bit microprocessor, Intel’s problematic iAPX432, was introduced in 1980. Soon
afterward, the concept of mainji-ame on a chip or micromainframe was used to indicate the
capabilities of these microprocessors and to distinguish them from previous 8- and 16-bit
microprocessors.
The introduction of several 32-bit microprocessors revolutionized the
microprocessor world. The performance of these 32-bit microprocessors is actually more
comparable to that of superminicomputers such as Digital Equipment Corporation’s
VAXl1/750 and VAX11/780. Designers of 32-bit microprocessors have implemented
many powerful features of these mainframe computers to increase the capabilities of
microprocessor chip sets: pipelining, on-chip cache memory, memory management, and
floating-point arithmetic.In pipelining, instruction fetch and execute cycles overlap. This method allows simultaneous preparation for execution of one or more instructions while another instruction is being executed. Pipelining was used for many years in mainframe and minicomputer CPUs to speed up the instruction execution time of these machines. The 32-bit microprocessors implement the pipelining concept and operate simultaneously on several 32-bit words, which may represent different instructions or part of a single instruction.
Although pipelining greatly increases the rate of execution of nonbranching code,
pipelines must be emptied and refilled each time a branch or jump instruction appears in
the code. This may slow down the processing rate for code with many branches or jumps.
Thus, there is an optimum pipeline depth, which is strongly related to the instruction set,
architecture, and gate density attainable on the processor chip.With memory management, virtual memory techniques, traditionally a feature of mainframes, are also implemented as on-chip hardware on typical 32-bit microprocessors.
This allows programmers to write programs much larger than those that could fit in the
main memory space available to microprocessors; the programs are simply stored on a
secondary device such as a hard disk, and portions of the program are swapped into main
memory as needed.Segmentation circuitry has been included in many 32-bit microprocessor chips.With this technique, blocks of code called segments, which correspond to modules of the
program and have varying sizes set by the programmer or compiler, are swapped. For many
applications, however, an alternative method borrowed from mainframes and superminis
calledpaging is used. Basically, paging differs from segmentation in that pages are of equal
size. Demandpaging, in which the operating system swaps pages automatically as needed,
can be used with all 32-bit microprocessors।
The 64-bit microprocessors such as Power PC 750 include all the features of 32-bit
microprocessors. In addition, they contain multiple on-chip integer and floating-point units
and a larger address and data buses. The 64-bit microprocessors can typically execute four
instructions per clock cycle and can run at a clock speed of over 2 GHz. The original Pentium
microprocessor is a CISC microprocessor. Pentium Pro and other succeeding members of
the Pentium family are designed using a combination of mostly microprogramming (CISC)
and some hardwired control (RISC) whereas the PowerPC is designed using hardwired
control with almost no microcode. The PowerPC is a RISC microprocessorand therefore
includes a simple instruction set. This instruction set includes register-to-register, load, and
store instructions. All instructions involving arithmetic operations use registers; load and
store instructions are utilized to access memory. Almost all computations can be obtained
from these simple instructions. Finally, 64-bit microprocessors are ideal candidates for
data-crunching machines and high-performance desktop systems and workstations.
Open Mobile Alliance (OMA)
The Open Mobile Alliance (OMA) was formed to promote global user adaptation of mobile services and applications by ensuring seamless interoperability. It was established on June 12, 2002. The work done by the Open Mobile Architecture and WAP fora laid the foundation of OMA. Later on Location Interoperability Forum (LIF), SyncML, Multi-Media Messaging Services Inter-Operability (MMS-IOP), Wireless Village, and Mobile Wireless Internet Forum (MWIF) joined the alliance by consolidating their efforts with the OMA. These fora were working individually in the same problem space of mobile services and applications. The LIF is promoting and working industry common solutions for the location based services. The SyncML is working on specifying an open standard for establishing a protocol between devices, applications and networks to ensure a consistent set of data available on any device or application at any time. The MMS-IOP is facilitating and coordinating MMS interoperability testing and problem solving. The Wireless Village is specifying the Internet based mobile instant messaging and presence services, all fully interoperable and leveraging existing web technologies. The MWIF was specifying an open mobile wireless and Internet architecture that is independent of the wireless access technology.
OMA harmonizes all these efforts and provides a common platform for the development of all these mobile services and applications.OMA is developing global open standards for services and applications independent of underlying wireless access technology, e.g. cdma2000, and WCDMA. It intends to provide seamless inter-technology and inter-generation roaming for services and applications across the globe. OMA has achieved its first milestone by developing specifications for OMA Download Feature Set.
The specification enables distribution and download of content data to mobile devices independent of vendor and content। It is an over the air protocol and features enhanced download reliability। The specification also provides protocols for associating Digital Rights Management (DRM) with content. DRM allows control of use and distribution of media content.OMA is a new organization compared to the other organizations discussed in this chapter, such as 3GPP, and 3GPP2. They have taken a mission that is very much needed to promote data services on wireless. OMA could play a key role in promoting the data over wireless in the future. The mobile services and applications is an important part of the wireless data industry, since it has direct interaction with the end users.
Development of this part can help boost wireless data usage। Currently, OMA is working on simplifying data application and content development for a mobile user. This includes work on the specifications related to the MMS. It is looking into providing a global standard for email notification on the wireless devices. OMA is working on script language for browsing environment. It is also working on the implementation of interoperability process and testing between its members.
IEEE 802
The Institute for Electrical and Electronic Engineers (IEEE) is a well-recognized body that was founded in 1884. The IEEE is a global technical, professional society serving the public interest and members in electrical, electronics, computer, information, and other technologies.The IEEE, which is based in the United States sponsors more than 300 conferences each year, including technical conferences, workshops, professional/careers/technical policy meetings, and standards working group meetings. In addition, the IEEE is involved in almost 200 "topical interest" meetings, either as consultants to the technical program or as nonfinancial partners.
The IEEE standards process consists of more than 30,000 volunteers and a Standards Board। IEEE is responsible for creating standards for the very popular local area networks (LAN) standards, such as 802.3 (also known as Ethernet), IEEE 802.5 (token ring), and 802.11 (wireless LAN).The standards process begins with the submission of a Project Authorization Request (PAR) to the Standards Board. According to IEEE, a PAR is the means by which standards projects are started. PARs define the scope, purpose, and contact points for the new project. If the Standards Board approves the PAR, then the standards process is initiated by the creation of a standards working group. The members of the standards working group are volunteers and may or may not be members of the IEEE.
The members of the IEEE working group create a draft standard. This draft is reviewed by a balloting group of IEEE members for review and approval. The constitution of the ballot group consists of standard's developers, potential users and others having general interest.Once this process is completed, the Standards Board conducts a review of the Final Draft Standard for the approval. Standards are typically reviewed once every five years for revision.One of the standards of interest to us is the IEEE 802 family, which is formally referred to as the IEEE 802 LAN/MAN Standards Committee. According to the IEEE, the IEEE 802 LAN/MAN Standards Committee develops local area network standards and metropolitan area network standards. The most widely used standards are for the Ethernet family, token ring, wireless LAN, bridging and virtual bridged LANs. An individual working group provides the focus for each area. IEEE 802 family standards and documents cover layers 1 and 2 of the OSI reference model.
This uses static encryption keys and does not have key distribution management। 802।11i will incorporate 802.1x that provides a framework for authenticating and controlling user traffic to a protected network. 802.1x provides dynamically varying encryption keys. It ties a protocol called Extensible Authentication Protocol (EAP) and provides multiple authentication methods, such as token cards, Kerberos, certificates, and public key authentication. 802.11i will use a stronger encryption algorithm such as Advanced Encryption Standard (AES). In summary, 802.11 task groups are exploring solutions for providing higher speed access, reduced interference, better quality management, strong security, and user roaming.
The IEEE standards process consists of more than 30,000 volunteers and a Standards Board। IEEE is responsible for creating standards for the very popular local area networks (LAN) standards, such as 802.3 (also known as Ethernet), IEEE 802.5 (token ring), and 802.11 (wireless LAN).The standards process begins with the submission of a Project Authorization Request (PAR) to the Standards Board. According to IEEE, a PAR is the means by which standards projects are started. PARs define the scope, purpose, and contact points for the new project. If the Standards Board approves the PAR, then the standards process is initiated by the creation of a standards working group. The members of the standards working group are volunteers and may or may not be members of the IEEE.
The members of the IEEE working group create a draft standard. This draft is reviewed by a balloting group of IEEE members for review and approval. The constitution of the ballot group consists of standard's developers, potential users and others having general interest.Once this process is completed, the Standards Board conducts a review of the Final Draft Standard for the approval. Standards are typically reviewed once every five years for revision.One of the standards of interest to us is the IEEE 802 family, which is formally referred to as the IEEE 802 LAN/MAN Standards Committee. According to the IEEE, the IEEE 802 LAN/MAN Standards Committee develops local area network standards and metropolitan area network standards. The most widely used standards are for the Ethernet family, token ring, wireless LAN, bridging and virtual bridged LANs. An individual working group provides the focus for each area. IEEE 802 family standards and documents cover layers 1 and 2 of the OSI reference model.
This uses static encryption keys and does not have key distribution management। 802।11i will incorporate 802.1x that provides a framework for authenticating and controlling user traffic to a protected network. 802.1x provides dynamically varying encryption keys. It ties a protocol called Extensible Authentication Protocol (EAP) and provides multiple authentication methods, such as token cards, Kerberos, certificates, and public key authentication. 802.11i will use a stronger encryption algorithm such as Advanced Encryption Standard (AES). In summary, 802.11 task groups are exploring solutions for providing higher speed access, reduced interference, better quality management, strong security, and user roaming.
IETF(Internet Engineering Yask Force).
The working and structure of IETF is different from a telecommunication standards body, such as 3GPP and 3GPP2. It is not driven by industry leaders, does not require membership or dues, and is open to any interested individual. This actually benefits the industry by opening up the platform for good ideas and opinions. At the same time, it makes the development of an open protocol slower compared to a telecom standards body.
The actual technical work of the IETF is done in its working groups (WGs), which are organized by topics into several areas. There are eight different areas in the IETF: application area, internet area, operations and management area, routing area, security area, sub-ip area, transport area, and user services area. Each WG has a charter and a set of work items. One chairperson (sometimes two), manages the WGs. The area directors (AD), who are collectively called IESGs, oversee the WGs. The WGs or areas are also overseen by the Internet Architecture Board (IAB), which is responsible for providing architectural oversight and focuses on long-range planning and coordination among the various areas. When members are interested in starting a new WG, they can form a "Birds of a Feather" (BOF) session. This is taken from the saying, "Birds of a feather flock together." If the BOF gathers sufficient interest and is thought to be working on a useful and solvable problem, a WG is formed.
WGs do most of their work using the e-mail distribution list. They meet three times a year for face-to-face meetings. Usually, a participant submits an Internet draft (ID) containing a solution for any of the WG's work items. The ID is discussed and its contents are agreed on by rough consensus. A WG may merge multiple solutions for different issues or the same issue into a WG ID. When all the issues are addressed, the WG chair calls for a last call for comments on the WG ID. After the comments are successfully addressed, the ID is sent to the IESG. The IESG also issues the last call for comments on the ID, but from all IETF participants. After all the comments are considered, the draft is sent to the request for comments (RFC) editor for publication as an RFC. RFCs are permanent IETF publications available as specifications to the users.
In addition to the liaisons and BOFs, there is a lot of focus inside IETF on developing protocols/recommendations that are also friendly to different wireless technology. Individuals from 3GPP, 3GPP2, Bluetooth, and the WLAN industry are working in different WGs to get solutions that would help in bringing IP to their technologies. Examples of such WGs are Performance Implications of Link Characteristics (PILC), Seamless Mobility (SEAMOBY), Session Initiation Protocol (SIP), Mobile Ad-Hoc Networks (MANET), Mobile IP, Zero Configuration Networks (ZeroConf), and Robust Header Compression (ROHC). This trend will increase due to the open nature of IETF.
The actual technical work of the IETF is done in its working groups (WGs), which are organized by topics into several areas. There are eight different areas in the IETF: application area, internet area, operations and management area, routing area, security area, sub-ip area, transport area, and user services area. Each WG has a charter and a set of work items. One chairperson (sometimes two), manages the WGs. The area directors (AD), who are collectively called IESGs, oversee the WGs. The WGs or areas are also overseen by the Internet Architecture Board (IAB), which is responsible for providing architectural oversight and focuses on long-range planning and coordination among the various areas. When members are interested in starting a new WG, they can form a "Birds of a Feather" (BOF) session. This is taken from the saying, "Birds of a feather flock together." If the BOF gathers sufficient interest and is thought to be working on a useful and solvable problem, a WG is formed.
WGs do most of their work using the e-mail distribution list. They meet three times a year for face-to-face meetings. Usually, a participant submits an Internet draft (ID) containing a solution for any of the WG's work items. The ID is discussed and its contents are agreed on by rough consensus. A WG may merge multiple solutions for different issues or the same issue into a WG ID. When all the issues are addressed, the WG chair calls for a last call for comments on the WG ID. After the comments are successfully addressed, the ID is sent to the IESG. The IESG also issues the last call for comments on the ID, but from all IETF participants. After all the comments are considered, the draft is sent to the request for comments (RFC) editor for publication as an RFC. RFCs are permanent IETF publications available as specifications to the users.
In addition to the liaisons and BOFs, there is a lot of focus inside IETF on developing protocols/recommendations that are also friendly to different wireless technology. Individuals from 3GPP, 3GPP2, Bluetooth, and the WLAN industry are working in different WGs to get solutions that would help in bringing IP to their technologies. Examples of such WGs are Performance Implications of Link Characteristics (PILC), Seamless Mobility (SEAMOBY), Session Initiation Protocol (SIP), Mobile Ad-Hoc Networks (MANET), Mobile IP, Zero Configuration Networks (ZeroConf), and Robust Header Compression (ROHC). This trend will increase due to the open nature of IETF.
3GPP2
The Third-Generation Partnership Project 2 (3GPP2) is a collaborative effort for generating 3G specifications for providing high-speed IP-based mobile systems. It was established for developing global specifications for network evolution from ANSI/TIA/EIA-41 to 3G, and global specifications for the radio transmission technologies supported by ANSI/TIA/EIA-41. 3GPP2 is mainly supported in North America, China, Japan, and South Korea and continues to play a dominant role in bringing IP technology to these cellular markets. 3GPP2 was born out of the International Telecommunication Union's (ITU) International Mobile Telecommunications-2000 (IMT-2000) initiative for providing high-speed data over the wireless network.
Although discussions did take place between ETSI and the ANSI-41 community to consolidate collaboration efforts for 3G, in the end it was deemed appropriate to establish 3GPP2 as a parallel partnership project. However, ETSI (3GPP Secretariat) is an observer in 3GPP2, and TIA (3GPP2 Secretariat) is an observer in 3GPP. In addition, the groups collaborated through seminars to address interworking of the CN and radio access technologies between these two projects. These bridges have helped to foster openness, cooperation, and goodwill among the participants of each project.
3GPP2 is a collaborative agreement between telecommunications standards development organizations (SDOs), which are called organizational partners (OPs). The five officially recognized OPs are: ARIB, CWTS, TIA, TTA, and TTC. 3GPP2 requires that a participating individual member company be affiliated with at least one of the OPs. 3GPP2 has market representation partners (MRPs) such as CDMA Development Group (CDG), and IPv6 Forum. They provide guidance to 3GPP2 so the specifications meet the market requirements for services, features, and functionalities.
The functional organization of 3GPP2 consists of a steering committee (SC), which manages the overall work process and adopting the technical specifications. The SC is composed of OPs and MRPs. The work of producing technical specifications is done by five TSGs. The TSGs meet, on average, ten times a year to produce technical specifications and reports. Each of the TSGs is comprised of representatives from the individual member companies. TSG-A deals with the access to network interface specifications (e.g., A interface). It also covers Abis and BSC to BTS interface specifications. TSG-C specifies cdma2000 air interface specifications. It also covers base station performance, channel codec, and conformance test specifications. Together, TSG-A and TSG-C are responsible for the radio access networks based on cdma2000. TSG-N specifies Layer 3 protocols for mobility management, call control, and other CN protocols and functionalities. It also covers wireless intelligent network (WIN) services. TSG-P works on wireless packet data interworking. It is responsible for data services and applications.
Although discussions did take place between ETSI and the ANSI-41 community to consolidate collaboration efforts for 3G, in the end it was deemed appropriate to establish 3GPP2 as a parallel partnership project. However, ETSI (3GPP Secretariat) is an observer in 3GPP2, and TIA (3GPP2 Secretariat) is an observer in 3GPP. In addition, the groups collaborated through seminars to address interworking of the CN and radio access technologies between these two projects. These bridges have helped to foster openness, cooperation, and goodwill among the participants of each project.
3GPP2 is a collaborative agreement between telecommunications standards development organizations (SDOs), which are called organizational partners (OPs). The five officially recognized OPs are: ARIB, CWTS, TIA, TTA, and TTC. 3GPP2 requires that a participating individual member company be affiliated with at least one of the OPs. 3GPP2 has market representation partners (MRPs) such as CDMA Development Group (CDG), and IPv6 Forum. They provide guidance to 3GPP2 so the specifications meet the market requirements for services, features, and functionalities.
The functional organization of 3GPP2 consists of a steering committee (SC), which manages the overall work process and adopting the technical specifications. The SC is composed of OPs and MRPs. The work of producing technical specifications is done by five TSGs. The TSGs meet, on average, ten times a year to produce technical specifications and reports. Each of the TSGs is comprised of representatives from the individual member companies. TSG-A deals with the access to network interface specifications (e.g., A interface). It also covers Abis and BSC to BTS interface specifications. TSG-C specifies cdma2000 air interface specifications. It also covers base station performance, channel codec, and conformance test specifications. Together, TSG-A and TSG-C are responsible for the radio access networks based on cdma2000. TSG-N specifies Layer 3 protocols for mobility management, call control, and other CN protocols and functionalities. It also covers wireless intelligent network (WIN) services. TSG-P works on wireless packet data interworking. It is responsible for data services and applications.
3GPP
The European Telecommunication Standards Institute (ETSI) pioneered the concept of "Partnership Project" in telecommunications by establishing Third-Generation Partnership Project (3GPP) in December 1998. 3GPP was initiated as a global initiative for a single globally common 3G standard. However, different cellular operators in the three largest telecommunication market sectors—America/South Korea, Japan, and Europe—went in their own ways in determining the choice of technology. 3GPP was able to attract a large portion of the cellular market by providing both TDMA- and CDMA-based solutions. It is expected that almost all of the existing GSM-based networks will evolve into 3GPP-based solutions. Some of the IS-136 operators (e.g., ATT Wireless Systems) have also adopted 3GPP-based solutions.
The scope of 3GPP is to produce globally applicable technical specifications and reports for 3G systems based on evolved GSM core networks (CNs) and the radio access technologies (RATs) supported by the CN. For the evolved CN, 3GPP has produced specifications for the general packet radio service (GPRS) system. For the RAT, it has produced specifications for enhanced data rates for GSM evolution (EDGE) and wideband CDMA (WCDMA) technologies.3GPP is a collaboration agreement that brings together a number of telecommunications standards bodies, which are called organizational partners (OPs), for developing specifications for wireless packet networks.
The current OPs are the Association of Radio Industries and Businesses-Japan (ARIB), China Wireless Telecommunication Standards Group (CWTS), ETSI, T1, Telecommunications Technology Association-Korea (TTA), and Telecommunications Technology Committee-Japan (TTC). 3GPP has also included industry fora and consortiums as market representation partners (MRPs). Some of the MRPs are 3G.IP, Global Mobile Suppliers Association (GSA), GSM Association, IPv6 Forum, UMTS Forum, Universal Wireless Communication Consortium (UWCC), and WMF. They provide guidance to the process so the standards meet the market requirements for services, features, and functionality.The functional organization of 3GPP consists of a project coordination group (PCG) that administers the work of technical specifications groups (TSGs). PCG is composed of OPs and MRPs. There are five TSGs, each with an area of responsibility. The TSG core network (TSG CN) is responsible for the specifications of the CN part of the system. Some of the important areas covered by TSG CN are user equipment, CN Layer 3 radio protocols (call control, session management, mobility management), signaling between the CN nodes, interconnection with external networks, O&M (Operation & Management) requirements, and mapping of QoS. TSG GSM/EDGE radio access network (TSG GERAN) is responsible for the specification of the radio access part of GSM/EDGE. It covers radio interface protocol layers, OA&M specifications for the RAN nodes, internal (Abis, Ater) and external (A, Gb) interfaces, and conformance test specifications for GERAN base stations and terminals. TSG radio access network (TSG RAN) is responsible for definition of the functions, requirements, and interfaces of the UMTS Terrestrial Radio Access network (UTRAN).
The scope of 3GPP is to produce globally applicable technical specifications and reports for 3G systems based on evolved GSM core networks (CNs) and the radio access technologies (RATs) supported by the CN. For the evolved CN, 3GPP has produced specifications for the general packet radio service (GPRS) system. For the RAT, it has produced specifications for enhanced data rates for GSM evolution (EDGE) and wideband CDMA (WCDMA) technologies.3GPP is a collaboration agreement that brings together a number of telecommunications standards bodies, which are called organizational partners (OPs), for developing specifications for wireless packet networks.
The current OPs are the Association of Radio Industries and Businesses-Japan (ARIB), China Wireless Telecommunication Standards Group (CWTS), ETSI, T1, Telecommunications Technology Association-Korea (TTA), and Telecommunications Technology Committee-Japan (TTC). 3GPP has also included industry fora and consortiums as market representation partners (MRPs). Some of the MRPs are 3G.IP, Global Mobile Suppliers Association (GSA), GSM Association, IPv6 Forum, UMTS Forum, Universal Wireless Communication Consortium (UWCC), and WMF. They provide guidance to the process so the standards meet the market requirements for services, features, and functionality.The functional organization of 3GPP consists of a project coordination group (PCG) that administers the work of technical specifications groups (TSGs). PCG is composed of OPs and MRPs. There are five TSGs, each with an area of responsibility. The TSG core network (TSG CN) is responsible for the specifications of the CN part of the system. Some of the important areas covered by TSG CN are user equipment, CN Layer 3 radio protocols (call control, session management, mobility management), signaling between the CN nodes, interconnection with external networks, O&M (Operation & Management) requirements, and mapping of QoS. TSG GSM/EDGE radio access network (TSG GERAN) is responsible for the specification of the radio access part of GSM/EDGE. It covers radio interface protocol layers, OA&M specifications for the RAN nodes, internal (Abis, Ater) and external (A, Gb) interfaces, and conformance test specifications for GERAN base stations and terminals. TSG radio access network (TSG RAN) is responsible for definition of the functions, requirements, and interfaces of the UMTS Terrestrial Radio Access network (UTRAN).
3GPP RAN Evolution
Second-generation GSM networks that were introduced in the early 1990s have experienced phenomenal growth over the last decade and have become the predominant wireless technology in the world today, with a market share of 70% or more. While the acceptance and numbers of subscribers in wireless cellular networks has been growing rapidly, the other phenomenon of the 1990s has been the exponential growth of the Internet and the number of Internet users. We have in essence a wireless network that primarily serves voice and messaging (SMS), and the Internet, which is a data-centric network that offers information, entertainment, e-commerce, and a slew of other services. With the natural evolution toward convergence of voice and data networks and the demand for Internet access and data services in wireless cellular networks, radio technologies defined for second-generation digital networks are evolving to accommodate packet data and services based on packet networks.
The initial GSM specifications provided only basic transmission capabilities for supporting data services. Data rates were in the 9.6-Kbps range. Release 96 specified high-speed circuit switched data services (HSCSD). The theoretical limit of HSCSD with 14.4-Kbps channel coding is 115.2 Kbps. However, practical limits allow data rates up to 64 Kbps.
After five years of intense standardization efforts, the result is an evolution path for GSM that is seen to be smooth, competitive, and cost-efficient. The first steps of this evolution were specified in Release 97 standards when GPRS was introduced. GPRS is able to deliver packet data services efficiently over existing GSM networks. The theoretical maximum throughput in GPRS networks is 160 Kbps per mobile station using all eight channels without error correction.
Voice capacity in wireless networks has always been an issue. In order to maximize the ROI (return on investment), operators have been asking for higher voice capacity over the existing spectrum. Adaptive multirate codec (AMR), which is included in Release 98, increased the spectral efficiency and quality of speech services significantly. The AMR codec contains a set of fixed-rate speech and channel codecs in addition to fast inband signaling and link adaptation. It operates in the full-rate and half-rate GSM channel modes.
Enhanced data rates for GDM evolution (EDGE) was introduced in Release 99. EDGE introduced more efficient modulation, coding, and retransmission schemes. The net effect of this was a significant boost to the performance of data services. EDGE as specified will enhance the throughput per time slot of both HSCSD and GPRS. Enhancement to HSCSD is called ECSD (enhanced circuit switched data), and enhancement to GPRS is called EGPRS (enhanced general packet radio service). ECSD in reality is not implemented since EGPRS is a superior mechanism for packet data access. The enhancement is equivalent to tripling the data rates for HSCSD and GPRS. This is accomplished by using 8-PSK modulation in addition to the existing GMSK. EGPRS is built on top of GPRS. One major change in EGPRS over GPRS is the link quality control, which in EGPRS also supports incremental redundancy. EGPRS also includes QoS capabilities that allow support for real-time services as well.
The initial GSM specifications provided only basic transmission capabilities for supporting data services. Data rates were in the 9.6-Kbps range. Release 96 specified high-speed circuit switched data services (HSCSD). The theoretical limit of HSCSD with 14.4-Kbps channel coding is 115.2 Kbps. However, practical limits allow data rates up to 64 Kbps.
After five years of intense standardization efforts, the result is an evolution path for GSM that is seen to be smooth, competitive, and cost-efficient. The first steps of this evolution were specified in Release 97 standards when GPRS was introduced. GPRS is able to deliver packet data services efficiently over existing GSM networks. The theoretical maximum throughput in GPRS networks is 160 Kbps per mobile station using all eight channels without error correction.
Voice capacity in wireless networks has always been an issue. In order to maximize the ROI (return on investment), operators have been asking for higher voice capacity over the existing spectrum. Adaptive multirate codec (AMR), which is included in Release 98, increased the spectral efficiency and quality of speech services significantly. The AMR codec contains a set of fixed-rate speech and channel codecs in addition to fast inband signaling and link adaptation. It operates in the full-rate and half-rate GSM channel modes.
Enhanced data rates for GDM evolution (EDGE) was introduced in Release 99. EDGE introduced more efficient modulation, coding, and retransmission schemes. The net effect of this was a significant boost to the performance of data services. EDGE as specified will enhance the throughput per time slot of both HSCSD and GPRS. Enhancement to HSCSD is called ECSD (enhanced circuit switched data), and enhancement to GPRS is called EGPRS (enhanced general packet radio service). ECSD in reality is not implemented since EGPRS is a superior mechanism for packet data access. The enhancement is equivalent to tripling the data rates for HSCSD and GPRS. This is accomplished by using 8-PSK modulation in addition to the existing GMSK. EGPRS is built on top of GPRS. One major change in EGPRS over GPRS is the link quality control, which in EGPRS also supports incremental redundancy. EGPRS also includes QoS capabilities that allow support for real-time services as well.
Wireless Network Evolution
On the mobile networking side, third-generation WCDMA technology will dominate the wide area access networks as well as licensed band hotspots. 802.11a and 802.11b wireless LAN technologies provide high data rates (on the order of 11 Mbps and 54 Mbps) and are ideally suited for hotspots such as airports, convention centers, and other public places. New WLAN security standard increases WLAN's significance, especially if the access provider does not have a license to operate a cellular network. Cellular operators are also interested in WLAN technologies and are in the process of building such networks to complement their wide area cellular service.
A nominal air interface bit rate of 2 Mbps in WCDMA hotspots is clearly less than WLAN can provide. However, direct bit rate comparison does not reflect the end user experience since WLAN lacks the QoS and smooth handover features that are standard in the WCDMA air interface. Advanced WCDMA radio resource control optimizes the access bandwidth usage, thus lowering operator costs and giving indirect savings to the subscriber.In the short term, the evolution of wireless networks is based on the technology path chosen. Third-generation license ownership is one of the major control points here (thus the high European auction prices).
Existing second-generation GSM, TDMA, or CDMA networks are another crucial factor when selecting a new technology. In the longer run one or two technologies will dominate the market. A small number of technologies can provide better economies of scale than multiple heterogeneous networks. Global roaming and other features are also easier to achieve when only a few interfaces must be matched. UMTS networks, WCDMA radio technology, and global radio band allocation have been major steps toward harmonizing the networks. The IETF Mobile IP working group is attempting to specify a universal mobility management mechanism with IPv6 technology.Personal area networks (PANs) are an interesting future development.
A single node ("personal base station" or "mobile router") passes traffic between the subscriber's personal area and the wide area, which is in the operator's domain. Technically a small-scale gateway between the domains is not that difficult as low-power integrated circuits can do most of the user plane processing, but the deployment scenarios are much harder: PAN management is a totally new issue; how trusted is the mobile router from the WAN perspective (and vice versa), Bluetooth devices already implement the required radio technology. Several control technologies related to security, QoS, and addressing are still under study in Bluetooth Forum and IETF Mobile ad hoc networks working groups. PAN use cases vary from cooperation of a mobile phone and embedded intelligence in an automobile to mobile phone-wireless earpiece-laptop communication.
A nominal air interface bit rate of 2 Mbps in WCDMA hotspots is clearly less than WLAN can provide. However, direct bit rate comparison does not reflect the end user experience since WLAN lacks the QoS and smooth handover features that are standard in the WCDMA air interface. Advanced WCDMA radio resource control optimizes the access bandwidth usage, thus lowering operator costs and giving indirect savings to the subscriber.In the short term, the evolution of wireless networks is based on the technology path chosen. Third-generation license ownership is one of the major control points here (thus the high European auction prices).
Existing second-generation GSM, TDMA, or CDMA networks are another crucial factor when selecting a new technology. In the longer run one or two technologies will dominate the market. A small number of technologies can provide better economies of scale than multiple heterogeneous networks. Global roaming and other features are also easier to achieve when only a few interfaces must be matched. UMTS networks, WCDMA radio technology, and global radio band allocation have been major steps toward harmonizing the networks. The IETF Mobile IP working group is attempting to specify a universal mobility management mechanism with IPv6 technology.Personal area networks (PANs) are an interesting future development.
A single node ("personal base station" or "mobile router") passes traffic between the subscriber's personal area and the wide area, which is in the operator's domain. Technically a small-scale gateway between the domains is not that difficult as low-power integrated circuits can do most of the user plane processing, but the deployment scenarios are much harder: PAN management is a totally new issue; how trusted is the mobile router from the WAN perspective (and vice versa), Bluetooth devices already implement the required radio technology. Several control technologies related to security, QoS, and addressing are still under study in Bluetooth Forum and IETF Mobile ad hoc networks working groups. PAN use cases vary from cooperation of a mobile phone and embedded intelligence in an automobile to mobile phone-wireless earpiece-laptop communication.
Mobile Office
The mobile office is essentially an extension of one's office via the mobile device. Many executives, doctors, engineers, and workers in industries such as finance, health care, and telecommunications feel the need to be connected to their office to access information as well as to be reachable. In the wireline oriented Internet world, VPNs have created an extension to corporate offices by extending the office to the user's home or any location in the world.
Wireless data networks provide employees access to information, enabling them to be productive and effective while away from the office. They can send and receive faxes or e-mail, log onto a company's LAN, search a database for product information, or even exchange computer files. Sales-people can complete sales orders, obtain the latest pricing, or check product availability on their own without requiring a support person at the main office. Field service personnel select work assignments, get directions and service details, check inventories, review parts lists or schematics, and even handle remotely without having to be close to a phone line.
With the increase in bit rates in third-generation wireless networks, we can now expect that users will be connected to the office via their mobile devices. Notebook computers with the appropriate access interfaces, which include 802.11 as well as GPRS, UMTS, and cdma2000, will enable connectivity to the workplace from any place. While it is possible today to achieve the mobile office concept via the Internet, it is limited to places that have Internet connectivity. The capability of being connected via wireless networks from anywhere will make this feature even more enticing and be a revenue source for operators who rely on business customers for a significant portion of their revenues.
The goal of mobile office-type applications is to provide users with the capability to handle professional and personal business whenever they want and wherever they want. Grabbing a cup of coffee and the Financial Times before boarding the morning train used to constitute the daily routine. While coffee will remain a staple, imagine a commute consisting of activities that traditionally would be done at home or at the office. Accessing the corporate intranet and e-mail, reading the latest industry news, and ordering flowers can be done on the wireless network today. Future applications will be even more dazzling. Order the latest movie release on the way home and it will be waiting on a playback device for immediate viewing. Order the new Lou Reed album and it will play on headphones in real time. Watch video highlights from last night's sporting events, or log onto the live camera at Waikiki Beach. The applications are endless but have one thing in common: a wireless data network that can handle data efficiently.
Wireless data networks provide employees access to information, enabling them to be productive and effective while away from the office. They can send and receive faxes or e-mail, log onto a company's LAN, search a database for product information, or even exchange computer files. Sales-people can complete sales orders, obtain the latest pricing, or check product availability on their own without requiring a support person at the main office. Field service personnel select work assignments, get directions and service details, check inventories, review parts lists or schematics, and even handle remotely without having to be close to a phone line.
With the increase in bit rates in third-generation wireless networks, we can now expect that users will be connected to the office via their mobile devices. Notebook computers with the appropriate access interfaces, which include 802.11 as well as GPRS, UMTS, and cdma2000, will enable connectivity to the workplace from any place. While it is possible today to achieve the mobile office concept via the Internet, it is limited to places that have Internet connectivity. The capability of being connected via wireless networks from anywhere will make this feature even more enticing and be a revenue source for operators who rely on business customers for a significant portion of their revenues.
The goal of mobile office-type applications is to provide users with the capability to handle professional and personal business whenever they want and wherever they want. Grabbing a cup of coffee and the Financial Times before boarding the morning train used to constitute the daily routine. While coffee will remain a staple, imagine a commute consisting of activities that traditionally would be done at home or at the office. Accessing the corporate intranet and e-mail, reading the latest industry news, and ordering flowers can be done on the wireless network today. Future applications will be even more dazzling. Order the latest movie release on the way home and it will be waiting on a playback device for immediate viewing. Order the new Lou Reed album and it will play on headphones in real time. Watch video highlights from last night's sporting events, or log onto the live camera at Waikiki Beach. The applications are endless but have one thing in common: a wireless data network that can handle data efficiently.
Evolution of Messaging
The Short Message Service (SMS) is a technology that was introduced in the early 1990s when the Internet was still unknown to the general public. SMS can be seen as the starting point of convergence between the Internet and the mobile world. In fact, long before the appearance of the Wireless Application Protocol (WAP) and other ways to access the Internet, wireless users were receiving simple information such as stock quotes, weather, train schedules, flight information, and access to e-mail using SMS. The widespread use of SMS is mainly due to the ability of young people to master the user interface and their desire to communicate cheaply with their friends even in situations where a phone call would not be possible. The popularity of SMS has definitely triggered the general interest in mobile data solutions and has shown to the industry the advantages of "always on" services, setting the stage for more evolved services.
The introduction of the SIM application toolkit standard opened a set of new opportunities: service providers can change or download applications in the wireless device over the air, and the user can be offered a menu-based choice of services, as well as support for new services and advanced security features such as those required for banking applications. However, at first only GSM subscribers could benefit from it and suffered all the inherent limitations of the SMS bearer: for example, limited bandwidth available and short message length.
The effort to overcome these constraints and allow wireless users easier access to Internet content regardless of the wireless technology led to the creation of the WAP standard. However, its popularity is still low, and WAP's true potential will be exploited when 2.5G and 3G packet switched services are introduced on a large scale.In the meantime, while WAP was being developed, SMS evolved. Proprietary protocols have appeared, such as Nokia's "Smart Messaging," and then standards were formed, such as Enhanced Message Services (EMS). EMS allows simultaneous downloading of ring tones, icons, and text, exploiting the current SMS network infrastructure.
The Mobile Station Application Environment (MMxE) standard, currently being defined by3GPP, will speed up the convergence between the Internet and the wireless world. MMxE aims at creating a standard environment for wireless applications by defining a Java environment on the phone and incorporates SIM card technology. In addition, MMxE supports standard Internet protocols for transport, security, and applications. Thanks to MMxE, in this environment, the wireless user has new possibilities that are currently available only to laptop and desktop computer users (e.g., download client applications such as interactive games, execute services on remote servers, and interact with another MMxE user in a variety of scenarios). MMxE is a powerful enabling technology for the multimedia message service (MMS) that will support messages combining text, images, sounds, and video clips in a variety of formats. MMS will be the first mobile service to utilize open Internet standards for messaging, such as multipurpose Internet mail extensions (MIME), Simple Mail Transfer Protocol (SMTP), and Hypertext Transfer Protocol (HTTP).
The introduction of the SIM application toolkit standard opened a set of new opportunities: service providers can change or download applications in the wireless device over the air, and the user can be offered a menu-based choice of services, as well as support for new services and advanced security features such as those required for banking applications. However, at first only GSM subscribers could benefit from it and suffered all the inherent limitations of the SMS bearer: for example, limited bandwidth available and short message length.
The effort to overcome these constraints and allow wireless users easier access to Internet content regardless of the wireless technology led to the creation of the WAP standard. However, its popularity is still low, and WAP's true potential will be exploited when 2.5G and 3G packet switched services are introduced on a large scale.In the meantime, while WAP was being developed, SMS evolved. Proprietary protocols have appeared, such as Nokia's "Smart Messaging," and then standards were formed, such as Enhanced Message Services (EMS). EMS allows simultaneous downloading of ring tones, icons, and text, exploiting the current SMS network infrastructure.
The Mobile Station Application Environment (MMxE) standard, currently being defined by3GPP, will speed up the convergence between the Internet and the wireless world. MMxE aims at creating a standard environment for wireless applications by defining a Java environment on the phone and incorporates SIM card technology. In addition, MMxE supports standard Internet protocols for transport, security, and applications. Thanks to MMxE, in this environment, the wireless user has new possibilities that are currently available only to laptop and desktop computer users (e.g., download client applications such as interactive games, execute services on remote servers, and interact with another MMxE user in a variety of scenarios). MMxE is a powerful enabling technology for the multimedia message service (MMS) that will support messages combining text, images, sounds, and video clips in a variety of formats. MMS will be the first mobile service to utilize open Internet standards for messaging, such as multipurpose Internet mail extensions (MIME), Simple Mail Transfer Protocol (SMTP), and Hypertext Transfer Protocol (HTTP).
IP Application
It is assumed that an MS is sending an e-mail message using SMTP. When the MS executes command to send an e-mail message, it invokes the underlying TCP layer. The TCP invocation causes the cdma2000 layer 3 functions to send an origination message with the data service option to the BSC. The message is sent over the access channel of the air interface with layer 2 acknowledgment required. The BSC acknowledges the receipt of the message with a BSC acknowledgment order message.The BSC constructs the CM service request message, sends the message to the MSC, and starts timer T303. The MSC, after recognizing that the request is for data service, sends an assignment request message, without allocating any terrestrial circuit to the BSC, to request assignment of radio resources and starts timer T10. The BSC and the MS initiate the establishment for a radio traffic channel.
Now that the CC connection through the BSC and MSC is completed, the BSC initiates the data session connection through the PCF and PDSN. For this, the BSC sends an A9-setup-A8 message to the PCF to establish an A8 connection and starts timer TA8 setup. The PCF recognizes that no A10/A11 connection associated with the MS is available and selects a PDSN for the call. The PCF sends an A11 registration request message to the selected PDSN and starts timer T-regreq.
The PDSN validates the A11 registration request message and accepts the connection by returning an A11 registration reply message with an accept indication and the lifetime set to a preconfigured value. The A10/A11 connection, once established, will be periodically refreshed after every expiry of the lifetime timer. Upon establishment of the A10/A11 connection, the PCF completes A8 connection by transmitting an A9-connect-A8 message to the BSC. The BSC sends an assignment complete message to the MSC, thus completing CC connection through the MSC. In this way a bearer path is established to transport user plane data between the MS and the PDSN through the PCF/BSC.
The PPP connection establishment procedure is initiated at this point. The network may ask for the CHAP/PAP user authentication as part of this procedure, which involves AAA agents for the verification of the authentication information.At this point all the necessary signaling has been performed and the HA knows where it needs to send data for the MS. In the user plane path the IP packets sent by the e-mail application in the MS take different forms. The PPP layer encapsulates the IP packets into PPP frames. The radio frames go through the multiplex sublayer, which converts them into physical layer SDUs. On the network side the reverse operation takes place in the BSS and PDSN. The PCF tunnels the PPP frames using GRE tunnel to the PDSN.
Now that the CC connection through the BSC and MSC is completed, the BSC initiates the data session connection through the PCF and PDSN. For this, the BSC sends an A9-setup-A8 message to the PCF to establish an A8 connection and starts timer TA8 setup. The PCF recognizes that no A10/A11 connection associated with the MS is available and selects a PDSN for the call. The PCF sends an A11 registration request message to the selected PDSN and starts timer T-regreq.
The PDSN validates the A11 registration request message and accepts the connection by returning an A11 registration reply message with an accept indication and the lifetime set to a preconfigured value. The A10/A11 connection, once established, will be periodically refreshed after every expiry of the lifetime timer. Upon establishment of the A10/A11 connection, the PCF completes A8 connection by transmitting an A9-connect-A8 message to the BSC. The BSC sends an assignment complete message to the MSC, thus completing CC connection through the MSC. In this way a bearer path is established to transport user plane data between the MS and the PDSN through the PCF/BSC.
The PPP connection establishment procedure is initiated at this point. The network may ask for the CHAP/PAP user authentication as part of this procedure, which involves AAA agents for the verification of the authentication information.At this point all the necessary signaling has been performed and the HA knows where it needs to send data for the MS. In the user plane path the IP packets sent by the e-mail application in the MS take different forms. The PPP layer encapsulates the IP packets into PPP frames. The radio frames go through the multiplex sublayer, which converts them into physical layer SDUs. On the network side the reverse operation takes place in the BSS and PDSN. The PCF tunnels the PPP frames using GRE tunnel to the PDSN.
Mobile IP
The mobile IP service (RFC 2002) provides complete mobility to a user. The PDSN has the functionality of an FA. A user is assigned an HA in its home IP network. The MS is assigned an IP address, called home address, which is in the same subnet as the HA. The MS uses CoA (IP address of the FA) to register with the HA. Registration causes the HA to perform proxy ARP on the home subnet and begins intercepting all packets destined to the MN's home address. The HA also creates a binding between the home address of the MN and the care-of address specified in the Registration request. When the HA receives data for an MS, it forwards the data to the FA using CoA and the FA forwards the data to the MS. Packets destined for the MN are tunnelled using IP-in-IP tunnelling to the care-of address.
IP-in-IP tunnelling is specified in RFC 2003. Mobile IP allows an MS to be reachable regardless of whether it is roaming in a public or private network. The only criteria is that the care-of address and the home agent have public IP addresses that are globally routable. In case of private network access, the MS uses reverse tunneling via the FA to send the data through the private network.Mobile IP signaling is exchanged on the traffic channels over the air interface, which is an inefficient usage of the expensive radio resource. There are some improvements with respect to the base mobile IP protocol to make the signaling more RR efficient.
One such improvement is that the agent advertisement messages are not broadcast continuously and periodically by the PDSN to all the MS. Instead, they are sent to an MS after establishing PPP connection. Another improvement is that the PDSN can only repeat the advertisements a configurable number of times for an MS. Also, the PDSN stops sending the advertisements to an MS once it receives a registration request from the same MS. As mobile IP runs over the PPP connection, the mobile IP registration lifetime should be smaller than the PPP inactivity timer.
The MS-FA security procedure is provided by using MS-FA challenge/response mechanism as described in RFC 3012. It is initiated by the PDSN to authenticate a user in a visited domain upon user registration. The PDSN includes an MS-FA challenge extension in the agent advertisement. Since the advertisements are rarely sent, the PDSN includes the next challenge in the registration reply. The MS uses this next challenge in the next re-registration with this PDSN. The PDSN communicates the FA challenge response, received from the MS, to the home AAA server through the visited AAA server.
IP-in-IP tunnelling is specified in RFC 2003. Mobile IP allows an MS to be reachable regardless of whether it is roaming in a public or private network. The only criteria is that the care-of address and the home agent have public IP addresses that are globally routable. In case of private network access, the MS uses reverse tunneling via the FA to send the data through the private network.Mobile IP signaling is exchanged on the traffic channels over the air interface, which is an inefficient usage of the expensive radio resource. There are some improvements with respect to the base mobile IP protocol to make the signaling more RR efficient.
One such improvement is that the agent advertisement messages are not broadcast continuously and periodically by the PDSN to all the MS. Instead, they are sent to an MS after establishing PPP connection. Another improvement is that the PDSN can only repeat the advertisements a configurable number of times for an MS. Also, the PDSN stops sending the advertisements to an MS once it receives a registration request from the same MS. As mobile IP runs over the PPP connection, the mobile IP registration lifetime should be smaller than the PPP inactivity timer.
The MS-FA security procedure is provided by using MS-FA challenge/response mechanism as described in RFC 3012. It is initiated by the PDSN to authenticate a user in a visited domain upon user registration. The PDSN includes an MS-FA challenge extension in the agent advertisement. Since the advertisements are rarely sent, the PDSN includes the next challenge in the registration reply. The MS uses this next challenge in the next re-registration with this PDSN. The PDSN communicates the FA challenge response, received from the MS, to the home AAA server through the visited AAA server.
IP in UMTS Networks
Second-generation wireless digital networks have been around for the last decade and more.These networks have provided voice as the primary service. Data services were essentially an add-on to these networks. Typical data rates ranged from 9.6 to 14.4 Kbps.With the explosion of the Internet and the vast array of services and applications that the Internet enabled, users felt the need to access these services via wireless terminals. One of the impediments to providing data services in 2G networks was the limitation of low data rates, which are a result of the radio interface being designed to handle primarily voice. Second-generation radio networks were spectrally inefficient for handling packet data services.
Market trends in the mid-1990s drove networks toward convergence. So the telecom, datacom, and IT networks started network evolution toward a unification path. Wireless networks needed to capitalize on the Internet potential by creating an extension to the Internet via the wireless medium. This has been refered to in various publications as the wireless Internet. The wireless Internet is not a new network in itself but rather an extension of the existing Internet over wireless networks. However, in order to create this wireless Internet, next-generation networks had to provide higher data rates, enhanced air interfaces for supporting packet data, and quality of service for a rich variety of applications. In addition, the rapid increase in the number of wireless subscribers has fueled the need for improving the spectral efficiency and capacity of current networks for voice services as well. The ITU formed the IMT-2000 forum to address the needs of the mobile telecommunication industry, and this resulted in the creation of the driver for third-generation networks.
Requirements for 3G networks with respect to radio access networks, core networks, and data rates were specified by IMT-2000. The Universal Mobile Telecommunication System (UMTS) is an architecture that was developed to meet these 3G requirements.
This chapter introduces UMTS, which was introduced to provide 3G services and the introduction of a new radio access network to meet the 3G goals, referred to as UMTS terrestrial radio access networks (UTRAN). This chapter discusses the UMTS system architecture, radio network, and core network functionalities. It also explains how a UMTS network can be used to transport IP datagrams and enable applications based on IP to be available to the mobile/wireless user.
Market trends in the mid-1990s drove networks toward convergence. So the telecom, datacom, and IT networks started network evolution toward a unification path. Wireless networks needed to capitalize on the Internet potential by creating an extension to the Internet via the wireless medium. This has been refered to in various publications as the wireless Internet. The wireless Internet is not a new network in itself but rather an extension of the existing Internet over wireless networks. However, in order to create this wireless Internet, next-generation networks had to provide higher data rates, enhanced air interfaces for supporting packet data, and quality of service for a rich variety of applications. In addition, the rapid increase in the number of wireless subscribers has fueled the need for improving the spectral efficiency and capacity of current networks for voice services as well. The ITU formed the IMT-2000 forum to address the needs of the mobile telecommunication industry, and this resulted in the creation of the driver for third-generation networks.
Requirements for 3G networks with respect to radio access networks, core networks, and data rates were specified by IMT-2000. The Universal Mobile Telecommunication System (UMTS) is an architecture that was developed to meet these 3G requirements.
This chapter introduces UMTS, which was introduced to provide 3G services and the introduction of a new radio access network to meet the 3G goals, referred to as UMTS terrestrial radio access networks (UTRAN). This chapter discusses the UMTS system architecture, radio network, and core network functionalities. It also explains how a UMTS network can be used to transport IP datagrams and enable applications based on IP to be available to the mobile/wireless user.
GPRS Roaming
This section describes how roaming of GPRS users between different networks is supported, and in particular how practical aspects of roaming impact the network model and what type of technical solutions are adopted. GPRS roaming enables subscribers to access their GPRS services while connected to a visited network. Roaming requires the ability to connect GPRS operators so that subscribers can move from one network to another and still access the GPRS service they have subscribed to.
According to the specification, the GPRS network architecture does not specify the location of the GGSN (i.e., the GGSN can be located either in the visited network or in the home network). describes the two possible models: in model 1, the GGSN for a visited MS is in the visited network, and in model 2, the GGSN is in the home network. In model 1, routing is efficient since IP packets can be routed directly from the GGSN to the Internet. However, in such case the home network has no control over the service being provided in terms of the following.
Billing: Among other functions, the GGSN collects the charging information coming from the SGSN and generates additional charging information (e.g., based on packet volume). However, currently there isn't a fast solution to carry such charging information to the home network; therefore, service such as prepaid cannot be supported.
QoS: It is not possible to guarantee end-to-end QoS since the visited network may not have the ability to support the QoS requirements of the user beyond the GGSN.
Access to services: DNS queries, HTML searches, and other services will be provided by the visited network or by the public Internet.
In model 2, routing of IP packets may not be optimal. For example, if the MS is accessing a Web site local to the country of the visited network, packets will be routed from the Web server to the GGSN in the home network, then tunneled backward to the MS in the visited network through GTP. However, in such a scenario the home network has full control on the service provisioning, prepaid access, and end-to-end QoS.For these reasons, GPRS operators have come to the realization that in order to provide services to roaming users and at the same time maintain control of service provisioning, the GGSN needs to be located in the subscriber home network. The GSM Association has therefore recommended GPRS operators to provide roaming services by locating the GGSN in the home network.
According to the specification, the GPRS network architecture does not specify the location of the GGSN (i.e., the GGSN can be located either in the visited network or in the home network). describes the two possible models: in model 1, the GGSN for a visited MS is in the visited network, and in model 2, the GGSN is in the home network. In model 1, routing is efficient since IP packets can be routed directly from the GGSN to the Internet. However, in such case the home network has no control over the service being provided in terms of the following.
Billing: Among other functions, the GGSN collects the charging information coming from the SGSN and generates additional charging information (e.g., based on packet volume). However, currently there isn't a fast solution to carry such charging information to the home network; therefore, service such as prepaid cannot be supported.
QoS: It is not possible to guarantee end-to-end QoS since the visited network may not have the ability to support the QoS requirements of the user beyond the GGSN.
Access to services: DNS queries, HTML searches, and other services will be provided by the visited network or by the public Internet.
In model 2, routing of IP packets may not be optimal. For example, if the MS is accessing a Web site local to the country of the visited network, packets will be routed from the Web server to the GGSN in the home network, then tunneled backward to the MS in the visited network through GTP. However, in such a scenario the home network has full control on the service provisioning, prepaid access, and end-to-end QoS.For these reasons, GPRS operators have come to the realization that in order to provide services to roaming users and at the same time maintain control of service provisioning, the GGSN needs to be located in the subscriber home network. The GSM Association has therefore recommended GPRS operators to provide roaming services by locating the GGSN in the home network.
Security in Wireless IP Networks
Acknowledging the higher risk of security problems in wireless networks opens up new problems due to the inherent mobility functionality associated with wireless networks. While mobility is a great convenience to wireless users, it demands a lot of intelligence and complexity on the network side. Mobility provides that users can establish a wireless subscription with one service provider in their hometown and can roam nationally or internationally. This introduces a connection between roaming and security functionality that the users must be authenticated and authorized for gaining access to network services in the visiting network that they are currently roaming to. The user must provide credentials that are used to identify the home network where he or she belongs, and then the access is provided after performing the security functions. On the flip side, the security function also involves the home network to ensure that the user is a genuine user who has subscribed to its services.
There are numerous security protocols in use on the Internet. Specifically, taking mobility into consideration, IPSec (defined in RFC 2401) provides a robust security framework to satisfy the requirements of the wireless IP networks. It offers access control, connectionless integrity, data origin authentication, protection against replays (a form of partial sequence integrity), confidentiality (encryption), and limited traffic flow confidentiality. These security features are handled at the IP layer, offering protection for IP- and/or upper-layer protocols.
There are two traffic security protocols, the authentication header (AH) [RFC 2402] and the encapsulated security payload (ESP) [RFC 2406], that are used as part of the IPSec. AH provides connectionless integrity, data origin authentication, and an optional antireplay service. The ESP may provide confidentiality (encryption) and limited traffic flow confidentiality. It may also provide connectionless integrity, data origin authentication, and antireplay service. AH and ESP can be used individually or in combination with each other to provide a desired set of security services in IPv4 and IPv6.
A security association is uniquely identified by a triple consisting of a security parameter index (SPI), an IP destination address, and a security protocol (AH or ESP) identifier. Internet key exchange (IKE) is the default automated key management protocol to negotiate protocols and algorithms and to create security associations and generate authentication keys. A security policy database can be used as input data to the IKE.
There are numerous security protocols in use on the Internet. Specifically, taking mobility into consideration, IPSec (defined in RFC 2401) provides a robust security framework to satisfy the requirements of the wireless IP networks. It offers access control, connectionless integrity, data origin authentication, protection against replays (a form of partial sequence integrity), confidentiality (encryption), and limited traffic flow confidentiality. These security features are handled at the IP layer, offering protection for IP- and/or upper-layer protocols.
There are two traffic security protocols, the authentication header (AH) [RFC 2402] and the encapsulated security payload (ESP) [RFC 2406], that are used as part of the IPSec. AH provides connectionless integrity, data origin authentication, and an optional antireplay service. The ESP may provide confidentiality (encryption) and limited traffic flow confidentiality. It may also provide connectionless integrity, data origin authentication, and antireplay service. AH and ESP can be used individually or in combination with each other to provide a desired set of security services in IPv4 and IPv6.
A security association is uniquely identified by a triple consisting of a security parameter index (SPI), an IP destination address, and a security protocol (AH or ESP) identifier. Internet key exchange (IKE) is the default automated key management protocol to negotiate protocols and algorithms and to create security associations and generate authentication keys. A security policy database can be used as input data to the IKE.
The QoS Challenge
The challenge of QoS is not introduced by wireless networks alone, but it was realized with the introduction of new high-bandwidth applications on the Internet. Normal IP data services, referred to as background or best-effort services, like email, Web browsing, FTP, and telnet sessions can work fine without a need for QoS. As new applications like voice over IP, multimedia streaming, and other bandwidth-hungry applications come into existence, the need to manage, control, differentiate, and guarantee the desired service levels for the duration of the communications has become an important issue. The user perception of quality is determined by end-to-end factors like latency, jitter, throughput, bit-error rate, and bandwidth. QoS management and the associated traffic engineering mechanisms together provide desired service levels.
Providing end-to-end QoS between two communicating endpoints is not a trivial issue as they are separated by networks owned and operated by several operators. There must be common understanding of QoS service levels between the users and the network and across the network borders. One means to achieve this is by establishing service-level agreements (SLAs) between users and the network in the form of subscription levels and between network operators to enforce service guarantees. Presently, on the Internet, SLAs are established for the aggregated traffic from all users across various ISPs and backbone service providers to provide a guaranteed level of service usually in the form of uptime, bandwidth guarantees, and delays.
However, QoS differentiation occurs on an application or service basis or even on per user basis, meaning that all services are treated equally and users cannot request for a higher QoS for a VoIP call to enjoy a better communication experience. There is also an effect due to mobility on QoS. Frequent changes of CoA due to mobility and handover make it difficult to maintain the same QoS levels from one point of attachment to another. Over the past years a lot of work has been devoted to understanding, defining, and developing QoS architectures and protocols. The IETF Integrated Services (Inst-Serv) group has developed an integrated service model and QoS framework for QoS provisioning on the Internet.
IETF has also specified another method for QoS provisioning, called the Diffserv. It offers a scalable solution by not requiring establishment of per-flow states in the network, but by aggregating the flows into predefined service levels. Packet classification and per hop behavior (PHB) are the building blocks of the Diffserv networks. Broadly, two different PHB are defined expedited forwarding (EF), for delay-sensitive real-time data, and assured forwarding (AF) for noncritical data. There are further four divisions within the AF class. Further, DiffServ does not require prior end-to-end signaling, but the source node can perform packet classification by appropriately marking the IP packets with desired DSCP codes, corresponding to desired QoS levels.
Providing end-to-end QoS between two communicating endpoints is not a trivial issue as they are separated by networks owned and operated by several operators. There must be common understanding of QoS service levels between the users and the network and across the network borders. One means to achieve this is by establishing service-level agreements (SLAs) between users and the network in the form of subscription levels and between network operators to enforce service guarantees. Presently, on the Internet, SLAs are established for the aggregated traffic from all users across various ISPs and backbone service providers to provide a guaranteed level of service usually in the form of uptime, bandwidth guarantees, and delays.
However, QoS differentiation occurs on an application or service basis or even on per user basis, meaning that all services are treated equally and users cannot request for a higher QoS for a VoIP call to enjoy a better communication experience. There is also an effect due to mobility on QoS. Frequent changes of CoA due to mobility and handover make it difficult to maintain the same QoS levels from one point of attachment to another. Over the past years a lot of work has been devoted to understanding, defining, and developing QoS architectures and protocols. The IETF Integrated Services (Inst-Serv) group has developed an integrated service model and QoS framework for QoS provisioning on the Internet.
IETF has also specified another method for QoS provisioning, called the Diffserv. It offers a scalable solution by not requiring establishment of per-flow states in the network, but by aggregating the flows into predefined service levels. Packet classification and per hop behavior (PHB) are the building blocks of the Diffserv networks. Broadly, two different PHB are defined expedited forwarding (EF), for delay-sensitive real-time data, and assured forwarding (AF) for noncritical data. There are further four divisions within the AF class. Further, DiffServ does not require prior end-to-end signaling, but the source node can perform packet classification by appropriately marking the IP packets with desired DSCP codes, corresponding to desired QoS levels.
Idle Mobility
Cellular networks are operated by different service providers, and each service provider manages the network by dividing the network into manageable network areas in a hierarchical fashion, all the way down to the cell level. Mobile nodes are identified by location based on which cell the user is presently in. Cellular networks perform location management by continuously tracking the location of mobile nodes with the help information received from the mobile nodes. The location information determines the cell (or a larger network area) where the mobile node is currently located. The location information is broadcast to all the mobile nodes in the network or cell area.
When someone calls the user, the network infrastructure, and the mobile switching center in particular, retrieves the latest location information of the mobile node and delivers the call. Mobile nodes periodically update their location information to the network. These location updates are otherwise referred to as idle mobility because they are performed when the mobile nodes are not engaged in any active call or other services. These updates are mainly timer based or event based, in case the mobile nodes may cross the network management areas or even network borders into an area operated by a different service provider .
The IETF Mobile-IP Group has defined two different mobility mechanisms for IP, one for IPv4 and another one for IPv6. The fundamental principles are similar, but the protocol capabilities and definitions are quite different. The basic principle is to provide a local care of address (CoA) to the mobile node while it is away from the home network. The mobile node may have a permanent or home address assigned in the home network. The local CoA is provided by the visiting or foreign network where the mobile node is currently present. In IPv6, the mobile node can form its own local CoA through stateless address autoconfiguration by listening to the router advertisement messages from the routers serving that subnet.
The mobile node performs a registration or a binding to the home agent (HA) to indicate the local CoA. The HA creates a binding cache between the permanent address and the CoA to tunnel all the packets addressed to the permanent address to the CoA. The same binding is also established at the correspondent node (CN) if there are any active sessions with any nodes. Whenever the mobile node's network point of attachment changes, it obtains a new CoA and performs updates on the binding to the HA and CN. If the mobile is far away from the home or CN, it may take a more latency to update the binding. To reduce the frequency of these updates, micro or localized mobility management (LMM) mechanisms are proposed. Cellular-IP, Hawaii, Regional Registration, and heirarchical mobile IP (HMIP) are some of the techniques.
When someone calls the user, the network infrastructure, and the mobile switching center in particular, retrieves the latest location information of the mobile node and delivers the call. Mobile nodes periodically update their location information to the network. These location updates are otherwise referred to as idle mobility because they are performed when the mobile nodes are not engaged in any active call or other services. These updates are mainly timer based or event based, in case the mobile nodes may cross the network management areas or even network borders into an area operated by a different service provider .
The IETF Mobile-IP Group has defined two different mobility mechanisms for IP, one for IPv4 and another one for IPv6. The fundamental principles are similar, but the protocol capabilities and definitions are quite different. The basic principle is to provide a local care of address (CoA) to the mobile node while it is away from the home network. The mobile node may have a permanent or home address assigned in the home network. The local CoA is provided by the visiting or foreign network where the mobile node is currently present. In IPv6, the mobile node can form its own local CoA through stateless address autoconfiguration by listening to the router advertisement messages from the routers serving that subnet.
The mobile node performs a registration or a binding to the home agent (HA) to indicate the local CoA. The HA creates a binding cache between the permanent address and the CoA to tunnel all the packets addressed to the permanent address to the CoA. The same binding is also established at the correspondent node (CN) if there are any active sessions with any nodes. Whenever the mobile node's network point of attachment changes, it obtains a new CoA and performs updates on the binding to the HA and CN. If the mobile is far away from the home or CN, it may take a more latency to update the binding. To reduce the frequency of these updates, micro or localized mobility management (LMM) mechanisms are proposed. Cellular-IP, Hawaii, Regional Registration, and heirarchical mobile IP (HMIP) are some of the techniques.
Radio Link Efficiency
A radio interface is bandwidth constrained because it is bound to use limited spectrum. Although 3G networks claim to provide bit rates up to 2 Mbps, it is still a far cry from the 52.8 Mbps a very high data rate digital subscriber line (VDSL) can offer on a single twisted-pair copper loop. Similarly, bit rate of 11 Mbps in WLAN is no comparison to 1 Gbps of the gigabit Ethernet (IEEE 802.3). Therefore, it is highly desired to use the available bandwidth as efficiently as possible, so as to give the user a decent performance for IP compared to the wired world. Moreover, cellular operators pay a significant amount of their deployment costs in acquiring a spectrum. Therefore, radio link efficiency is also highly desired for cost savings.
One approach to improving efficiency for some IP protocols is to use header compression. A problem with IP is its large header overhead. This problem is more visible for those real-time applications where a packet is generated at a very fast rate and the payload size is comparable or even smaller to the header size. For example, an RTP (real-time protocol) packet carrying interactive voice conversation could have an IPv6 header of 40 bytes, a UDP header of 8 bytes, and an RTP header of 12 bytes, making the total header bytes equal to 60 bytes.
The size of the payload, depending on the speech coding, could be as low as 15 to 20 bytes. In this example the header size is twice the payload size. The Robust Header Compression ROHC working group has developed [RFC 3095] header compression schemes for RTP/UDP/IP. The schemes can reduce the header size down to one or zero byte. The wireless links also need to have robust header compression for the other protocols, such as TCP and SCTP.Bandwidth efficiency can also be improved by performing compression on IP payloads. The IP Payload Compression Protocol (IPComp) [RFC 2393] defines a framework for payload compression. The 3GPP2 network uses the PPP from the PDSN to the MS and has suggested using the PPP Compression Control Protocol [RFC 1962] for PPP payload compression. Bluetooth LAN access profile also suggests using PPP and PPP payload compression.
However, if the encryption is applied to IP datagrams, the compression at a lower layer (e.g., PPP) becomes ineffective. IPComp is especially useful when encryption is applied to IP datagrams. RFC 2757 provides a good analysis of the feasibility of IP payload compression. It suggests that IP payload compression is something of a niche optimization and may not be always useful. It also says that many of the IP payloads are already compressed (images, audio, video, "zipped" files) by the applications or are already encrypted above the IP layer. These payloads will not compress further, limiting the benefit of this optimization. Also, the application-level compression can often outperform IPComp because the applications can use compression dictionaries based on knowledge of the specific data being compressed. Therefore, for payload compression the best bandwidth efficiency can be achieved if application-level compression techniques are used extensively. The challenge is to ensure that all the applications have a compression mechanism and are using them over wireless links.
One approach to improving efficiency for some IP protocols is to use header compression. A problem with IP is its large header overhead. This problem is more visible for those real-time applications where a packet is generated at a very fast rate and the payload size is comparable or even smaller to the header size. For example, an RTP (real-time protocol) packet carrying interactive voice conversation could have an IPv6 header of 40 bytes, a UDP header of 8 bytes, and an RTP header of 12 bytes, making the total header bytes equal to 60 bytes.
The size of the payload, depending on the speech coding, could be as low as 15 to 20 bytes. In this example the header size is twice the payload size. The Robust Header Compression ROHC working group has developed [RFC 3095] header compression schemes for RTP/UDP/IP. The schemes can reduce the header size down to one or zero byte. The wireless links also need to have robust header compression for the other protocols, such as TCP and SCTP.Bandwidth efficiency can also be improved by performing compression on IP payloads. The IP Payload Compression Protocol (IPComp) [RFC 2393] defines a framework for payload compression. The 3GPP2 network uses the PPP from the PDSN to the MS and has suggested using the PPP Compression Control Protocol [RFC 1962] for PPP payload compression. Bluetooth LAN access profile also suggests using PPP and PPP payload compression.
However, if the encryption is applied to IP datagrams, the compression at a lower layer (e.g., PPP) becomes ineffective. IPComp is especially useful when encryption is applied to IP datagrams. RFC 2757 provides a good analysis of the feasibility of IP payload compression. It suggests that IP payload compression is something of a niche optimization and may not be always useful. It also says that many of the IP payloads are already compressed (images, audio, video, "zipped" files) by the applications or are already encrypted above the IP layer. These payloads will not compress further, limiting the benefit of this optimization. Also, the application-level compression can often outperform IPComp because the applications can use compression dictionaries based on knowledge of the specific data being compressed. Therefore, for payload compression the best bandwidth efficiency can be achieved if application-level compression techniques are used extensively. The challenge is to ensure that all the applications have a compression mechanism and are using them over wireless links.
CDMA IS-95-A/IS-95-B Data Networks
The success of the wireless industry led to the search for new technologies to increase the capacity of wireless systems without requiring additional spectrum. Code Division Multiple Access, or CDMA, was one such digital technology developed to address this need for capacity. It provides increased spectrum efficiency or, in other words, allows multiple users to share the same radio spectrum more efficiently. The actual quantitative improvement over existing analog systems and over competing digital technologies is still a subject of intense debate.CDMA is a spread spectrum technology, which means that instead of dividing RF spectrum into narrow channels (e.g., 30 KHz each) and assigning one (AMPS) or more (e.g., TIA/EIA/IS-136 TDMA) conversations to each channel, it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal.
A CDMA call compresses a digital 64-Kbps stream into a standard rate of 9600 bps (or 14400 bps). This is then spread to a transmitted rate of about 1.2288 Mbps. Spreading is done by applying digital codes, unique to each user, to the data bits associated with users in a cell. The spread signal is transmitted along with the signals of all the other users in that cell over a 1.25 MHz channel. When the signal is received, the codes are removed from the desired signal, separating the users and returning the call to a rate of 9600 bps (or 14400 bps). This primary channel is called the fundamental channel (FCH).
In the United States, the spectrum is divided into two bands: one for ordinary public mobile telephony service in the 800-MHz frequency band and the other for PCS services in the 1900-MHz frequency band. New digital wireless technologies operating in the 800-MHz band are required to be compatible with AMPS. The radio functionalities for the 800-MHz band are specified in TIA/EIA-95-A and TIA/EIA-95-B and include AMPS compatibility specification. Those for the 1900-MHz band are specified in ANSI J-STD 008. There is essentially no difference in the CDMA-related functionality between the two standards. The service options for wireless data are specified in TIA/EIA/IS-707.
TIA/EIA/IS-95-A was developed primarily to provide increased voice capacity. Support for data was initially limited to circuit-switched (CS) data. CS data requires that a dedicated connection be maintained between the endpoints in the network at all times in the duration of the CS data call. This implies that a dedicated radio channel is maintained even if no data is being transferred. However, for most applications, the data traffic is bursty, and this results in an inefficient utilization of scarce radio spectrum with CS data.
A CDMA call compresses a digital 64-Kbps stream into a standard rate of 9600 bps (or 14400 bps). This is then spread to a transmitted rate of about 1.2288 Mbps. Spreading is done by applying digital codes, unique to each user, to the data bits associated with users in a cell. The spread signal is transmitted along with the signals of all the other users in that cell over a 1.25 MHz channel. When the signal is received, the codes are removed from the desired signal, separating the users and returning the call to a rate of 9600 bps (or 14400 bps). This primary channel is called the fundamental channel (FCH).
In the United States, the spectrum is divided into two bands: one for ordinary public mobile telephony service in the 800-MHz frequency band and the other for PCS services in the 1900-MHz frequency band. New digital wireless technologies operating in the 800-MHz band are required to be compatible with AMPS. The radio functionalities for the 800-MHz band are specified in TIA/EIA-95-A and TIA/EIA-95-B and include AMPS compatibility specification. Those for the 1900-MHz band are specified in ANSI J-STD 008. There is essentially no difference in the CDMA-related functionality between the two standards. The service options for wireless data are specified in TIA/EIA/IS-707.
TIA/EIA/IS-95-A was developed primarily to provide increased voice capacity. Support for data was initially limited to circuit-switched (CS) data. CS data requires that a dedicated connection be maintained between the endpoints in the network at all times in the duration of the CS data call. This implies that a dedicated radio channel is maintained even if no data is being transferred. However, for most applications, the data traffic is bursty, and this results in an inefficient utilization of scarce radio spectrum with CS data.
IS-136 Teleservices
IS-136 teleservices are a feature of IS-136 networks that have been developed to speed up the introduction of new services for IS-136 users. A teleservice is an application that uses the air interface and network interface as the bearers for transport between a server and a mobile station. In other words, a teleservice uses the mobile station connection through the cellular network as a "bit-pipe" to exchange information with the mobile station.Teleservices allow service providers to deliver data units to mobile stations that are connected using either DCCH or DTC. Teleservices are possible both when the user is roaming or in the home network. The data units can contain data for user applications or programming information for the mobile station. Teleservices can be either point-to-point or broadcast.
The following teleservices have been defined and standardized for IS-136:
Cellular messaging teleservice (CMT): The teleservice used to provide short message service to mobile users. Alphanumeric messages can be sent to and from mobile stations, therefore allowing for a two-way data service. TSAR can be used for CMT to sends messages longer than what IS-136 and IS-41 allow. CMT messages can be carried over DTC, DCCH, or S-BCCH (for broadcast teleservices).
Over-the-air activation teleservice (OATS): The teleservice used to provide over-the-air activation (OAA); that is, a method to program a mobile station with the home service provider network information (e.g., the identifier of the service provider), the A key for security, the mobile station identity (MSID), and other information. OATS requires the capability to exchange two-way R-DATA, and teleservice segmentation and reassembly protocol (TSAR) may be applied to send messages longer than what IS-136 and IS-41 allow. OATS messages can be carried on DTC or DCCH but not on S-BCCH, since OATS messages are always directed to a single mobile station.
Over-the-air programming teleservice (OPTS): The teleservice used to provide over-the-air activation (OAA); that is, a method for programming non-NAM (number assignment module) data in the mobile station (i.e., information regarding the intelligent roaming database, IRDB). OPTS is a mobile terminated teleservice between the network and a mobile station and can be carried over DTC, DCCH, or S-BCCH. TSAR may be used as in the previous cases.Generic UDP transport teleservice (GUTS): The application data delivery teleservice that supports the thin client architecture (TCA) for the delivery of text-based information from World Wide Web sites to mobile stations through the cellular network. GUTS is a two-way teleservice that adopts the User Data Protocol (UDP) to identify the port where the data are to be delivered in order to be received by the correct application (e.g., the port for the WAP browser in the mobile station). The WAP browser allows the mobile user to access the Internet from the mobile station through WAP-enabled Web pages. GUTS messages can be carried over DTC, DCCH, and S-BCCH.
The following teleservices have been defined and standardized for IS-136:
Cellular messaging teleservice (CMT): The teleservice used to provide short message service to mobile users. Alphanumeric messages can be sent to and from mobile stations, therefore allowing for a two-way data service. TSAR can be used for CMT to sends messages longer than what IS-136 and IS-41 allow. CMT messages can be carried over DTC, DCCH, or S-BCCH (for broadcast teleservices).
Over-the-air activation teleservice (OATS): The teleservice used to provide over-the-air activation (OAA); that is, a method to program a mobile station with the home service provider network information (e.g., the identifier of the service provider), the A key for security, the mobile station identity (MSID), and other information. OATS requires the capability to exchange two-way R-DATA, and teleservice segmentation and reassembly protocol (TSAR) may be applied to send messages longer than what IS-136 and IS-41 allow. OATS messages can be carried on DTC or DCCH but not on S-BCCH, since OATS messages are always directed to a single mobile station.
Over-the-air programming teleservice (OPTS): The teleservice used to provide over-the-air activation (OAA); that is, a method for programming non-NAM (number assignment module) data in the mobile station (i.e., information regarding the intelligent roaming database, IRDB). OPTS is a mobile terminated teleservice between the network and a mobile station and can be carried over DTC, DCCH, or S-BCCH. TSAR may be used as in the previous cases.Generic UDP transport teleservice (GUTS): The application data delivery teleservice that supports the thin client architecture (TCA) for the delivery of text-based information from World Wide Web sites to mobile stations through the cellular network. GUTS is a two-way teleservice that adopts the User Data Protocol (UDP) to identify the port where the data are to be delivered in order to be received by the correct application (e.g., the port for the WAP browser in the mobile station). The WAP browser allows the mobile user to access the Internet from the mobile station through WAP-enabled Web pages. GUTS messages can be carried over DTC, DCCH, and S-BCCH.
The Digital PCS Standards
The digital PCS standards comprise an interim standard (IS), to indicate that the standard is not yet approved by the TIA/EIA (Telecommunication Industry Association-Electronic Industry Association). However, these standards have achieved the status of TIA/EIA standards but are commonly referred to with their "IS" code (e.g., IS-136).As described in this chapter, the term IS-136 network refers to the cellular standard defined by the TIA for digital PCS networks. In particular, IS-136 identifies a particular part of the digital PCS family of standards and does not identify all the features of digital PCS networks.
The IS-136 standard is the result of the evolution of the North American analog cellular systems called advanced mobile phone service (AMPS). Due to the phenomenal success of AMPS networks, the need for a more efficient system and more cellular capacity led to the development of a first digital cellular standard, called IS-54. However, IS-54 drawbacks (higher costs with no clear improvements for the end users) did not allow IS-54 to duplicate the success of AMPS. Therefore, the IS-136 standard was developed to allow for increased cellular capacity and for providing new services to mobile users.
IS-136 allowed for a capacity three times larger than the one provided by AMPS, and for new features such as longer battery life, authentication and voice privacy, caller ID, message waiting indication, and short messages. Whereas AMPS systems used analog traffic and control channels, IS-54 introduced a DTC. Full-rate DTC is supported in IS-54 by means of time multiplexing of 30-KHz RF channels, and a mobile user is assigned a full-rate DTC. In addition to the DTC, IS-136 introduced the DCCH, which allows for the new features supported by IS-136 with respect to its predecessors.
IS-136: Mobile Station-Base Station Compatibility Standard. IS-136 describes the channels used in digital PCS from the physical layer to the network layer, focusing in particular on the DCCH. IS-137: Minimum Performance Standard for Mobile Stations. IS-137 defines the minimum requirements for the mobile station in terms of receiver, transmitter, and environmental requirements. Requirements for the receiver include frequency coverage, acquisition time, demodulation, bit error rate, and signal strength measurement accuracy. Requirements for the transmitter include frequency stability, power output, modulation type and stability, limitation of emissions, and time alignment. Environmental requirements include temperature, power supply voltage, humidity, vibration, and shock. The standard defines the minimum requirements and the method to measure them. IS-138: Minimum Performance Standard for Base Stations. IS-138 is the companion standard to IS-137 and defines the minimum requirements for the base station in terms of receiver, transmitter, and environmental requirements.
The IS-136 standard is the result of the evolution of the North American analog cellular systems called advanced mobile phone service (AMPS). Due to the phenomenal success of AMPS networks, the need for a more efficient system and more cellular capacity led to the development of a first digital cellular standard, called IS-54. However, IS-54 drawbacks (higher costs with no clear improvements for the end users) did not allow IS-54 to duplicate the success of AMPS. Therefore, the IS-136 standard was developed to allow for increased cellular capacity and for providing new services to mobile users.
IS-136 allowed for a capacity three times larger than the one provided by AMPS, and for new features such as longer battery life, authentication and voice privacy, caller ID, message waiting indication, and short messages. Whereas AMPS systems used analog traffic and control channels, IS-54 introduced a DTC. Full-rate DTC is supported in IS-54 by means of time multiplexing of 30-KHz RF channels, and a mobile user is assigned a full-rate DTC. In addition to the DTC, IS-136 introduced the DCCH, which allows for the new features supported by IS-136 with respect to its predecessors.
IS-136: Mobile Station-Base Station Compatibility Standard. IS-136 describes the channels used in digital PCS from the physical layer to the network layer, focusing in particular on the DCCH. IS-137: Minimum Performance Standard for Mobile Stations. IS-137 defines the minimum requirements for the mobile station in terms of receiver, transmitter, and environmental requirements. Requirements for the receiver include frequency coverage, acquisition time, demodulation, bit error rate, and signal strength measurement accuracy. Requirements for the transmitter include frequency stability, power output, modulation type and stability, limitation of emissions, and time alignment. Environmental requirements include temperature, power supply voltage, humidity, vibration, and shock. The standard defines the minimum requirements and the method to measure them. IS-138: Minimum Performance Standard for Base Stations. IS-138 is the companion standard to IS-137 and defines the minimum requirements for the base station in terms of receiver, transmitter, and environmental requirements.
Data in IS-136 Networks
IS-136 networks are commonly referred to as digital personal communications service (PCS) networks or TDMA networks. As described in this chapter, the term IS-136 network refers to the cellular standard defined by the Telecommunications Industry Associations (TIA) for digital PCS networks, called TIA/EIA 136. In this chapter we will use the term IS-136 for simplicity.IS-136 provides not only voice services but also a set of data services. This chapter describes the family of standards that compose an IS-136 network, the network architecture and protocols, and the data services offered by an IS-136 network.
The chapter focuses on the IS-136 data services before GPRS concepts were "imported" in the IS-136 architecture. The enhancements of IS-136 by GPRS concepts are only briefly described in this chapter in the section on evolution of IS-136, since the adoption of GPRS in IS-136 leads to an architecture and services very similar to the GSM/GPRS ones, described in.IS-136 is the result of the evolution of cellular systems in North America from analog AMPS to digital systems. IS-136 introduces the DCCH (digital control channel), which forms the core of the IS-136 specification, and provides new system functionality and supports enhanced features, including the sleep mode.
To preserve mobile station battery power, support of multiple vocoders, the ability to acquire seamlessly the same services both in the cellular band (800 MHz) and the PCS band (1900 MHz), and the support of teleservices to transfer application data to and from cellular phones.The IS-136 standard specifies two types of data services: teleservices and circuit switched data services. An IS-136 teleservice is an application that uses the air interface and network interface as the bearers for transporting a small quantity of bursty information (e.g., short messages) between a server and a mobile station.
Circuit switched data services enable data applications, such as fax and ISP connection, to exchange a possibly long flow of information over the digital traffic channel (DTC). The basic idea in providing DTC data service is to provide a circuit switched connection for carrying data from the user through the IS-136 network and vice versa. The establishment of the data connection is very similar to the establishment of a voice call.In the following sections we describe an overview of IS-136 network architecture and data services. We describe also the protocols and the functions provided by the IS-136 network for carrying data.
The chapter focuses on the IS-136 data services before GPRS concepts were "imported" in the IS-136 architecture. The enhancements of IS-136 by GPRS concepts are only briefly described in this chapter in the section on evolution of IS-136, since the adoption of GPRS in IS-136 leads to an architecture and services very similar to the GSM/GPRS ones, described in.IS-136 is the result of the evolution of cellular systems in North America from analog AMPS to digital systems. IS-136 introduces the DCCH (digital control channel), which forms the core of the IS-136 specification, and provides new system functionality and supports enhanced features, including the sleep mode.
To preserve mobile station battery power, support of multiple vocoders, the ability to acquire seamlessly the same services both in the cellular band (800 MHz) and the PCS band (1900 MHz), and the support of teleservices to transfer application data to and from cellular phones.The IS-136 standard specifies two types of data services: teleservices and circuit switched data services. An IS-136 teleservice is an application that uses the air interface and network interface as the bearers for transporting a small quantity of bursty information (e.g., short messages) between a server and a mobile station.
Circuit switched data services enable data applications, such as fax and ISP connection, to exchange a possibly long flow of information over the digital traffic channel (DTC). The basic idea in providing DTC data service is to provide a circuit switched connection for carrying data from the user through the IS-136 network and vice versa. The establishment of the data connection is very similar to the establishment of a voice call.In the following sections we describe an overview of IS-136 network architecture and data services. We describe also the protocols and the functions provided by the IS-136 network for carrying data.
SMS Cell Broadcast
SMS cell broadcast provides a mechanism to broadcast short messages from a radio network to the MSs in a cell area . The sources of SMSCB can come from broadcast applications, such as traffic reports and weather reports. The message is limited by the capacity of the broadcast channel that carries it. A single CB message can carry up to 88 bytes. The service broadcasts on a cell level because the SMS-CB uses a specially defined channel called CBCH. The presence of a CBCH is indicated by the system information messages broadcasted for an individual cell on the BCCH. The system information tells the MSs camped on a cell on which frequency and channel CB message are sent.
A CB message has a message header and a payload. The CB message header has an identifier, which identifies the source and subject of the SMSCB message. It also has a sequence number, which enables the MS to determine when a new message from a given source is available. SMS-CB messages are not acknowledged by the MS. Reception of SMS-CB messages by the MS is only possible in idle mode.The SMS cell broadcast service is designed to minimize the battery usage requirements for an MS. An MS can read the first part of a CB message and then decide whether or not to read the rest of the message.
In addition, the network may broadcast schedule messages, which provide information in advance about the CB messages that will be sent immediately afterward. The MS may use this scheduling information to restrict reception to those messages the customer is interested in receiving.The CB short messages are generated in the cell broadcast entity (CBE). The functionality of a CBE is not specified in the GSM standards. The CBE can be understood as a source of SMS-CB, such as a weather information center. It includes all aspects of formatting the CB messages as well as splitting a message into various segments, which will eventually be transmitted on one channel.
The CBC actually handles all the GSM related functions of SMS-CB. It may be getting input from multiple CBEs and could be connected to one or multiple BSCs. The CBC coordinates the formatting and organization of the messages it receives from the CBE into GSM form. It performs functions such as determining the rate at which certain messages must be delivered; setting the language; and determining area where a certain message is to be sent.The BSS takes care of the radio part of transmitting CB messages. The BSC performs functions such as storing the messages as long as they are to be transmitted; routing the messages to the appropriate BTSs; and scheduling of the CB messages according to the repetition rate. BTS puts the message on the CBCH at the time specified by the BSC.
A CB message has a message header and a payload. The CB message header has an identifier, which identifies the source and subject of the SMSCB message. It also has a sequence number, which enables the MS to determine when a new message from a given source is available. SMS-CB messages are not acknowledged by the MS. Reception of SMS-CB messages by the MS is only possible in idle mode.The SMS cell broadcast service is designed to minimize the battery usage requirements for an MS. An MS can read the first part of a CB message and then decide whether or not to read the rest of the message.
In addition, the network may broadcast schedule messages, which provide information in advance about the CB messages that will be sent immediately afterward. The MS may use this scheduling information to restrict reception to those messages the customer is interested in receiving.The CB short messages are generated in the cell broadcast entity (CBE). The functionality of a CBE is not specified in the GSM standards. The CBE can be understood as a source of SMS-CB, such as a weather information center. It includes all aspects of formatting the CB messages as well as splitting a message into various segments, which will eventually be transmitted on one channel.
The CBC actually handles all the GSM related functions of SMS-CB. It may be getting input from multiple CBEs and could be connected to one or multiple BSCs. The CBC coordinates the formatting and organization of the messages it receives from the CBE into GSM form. It performs functions such as determining the rate at which certain messages must be delivered; setting the language; and determining area where a certain message is to be sent.The BSS takes care of the radio part of transmitting CB messages. The BSC performs functions such as storing the messages as long as they are to be transmitted; routing the messages to the appropriate BTSs; and scheduling of the CB messages according to the repetition rate. BTS puts the message on the CBCH at the time specified by the BSC.
Data Services on Signaling/Broadcast Channels—SMS
The GSM technology is the first in providing data services on signaling and broadcast channels. These services are commonly known as SMS. There are two different types of SMS: SMS point-to-point and SMS broadcast. We will look into both of these services in this section. Data services like SMS are also provided by other radio technologies, such as IS-136 and IS-95.SMS point-to-point is the data service that uses only the signaling channel (SDCCH) to transport the data over the air interface. In SMS, a short string of text (maximum 126 characters) is carried from one subscriber to another.
There is another type of SMS service called SMS broadcast, which is the only broadcast channel data service. As the name implies, the user terminal can only receive the data broadcasted from the network. This service transports data on a specially defined broadcast channel, CBCH, over the air interface. This service is also limited to a short text string based on the carrying capacity of the CBCH. This service was anticipated to be used by the broadcast data applications, such as traffic reports and weather alerts. This service didn't get much attention from service providers because it didn't provide a good revenue generation model.
SMS point-to-point (SMS p-p) is a dedicated service between two users. GSM has defined two teleservices for SMS: SMS-MO (mobile origination), and SMS-MT (mobile termination). Using this service, a user sends a short string of alphanumeric characters to another user. SMS can also be used by the network operators to notify a user about certain status (e.g., number of messages waiting in voice mail). SMS is based on the concept that the signaling channel capacity can be utilized for carrying a few bytes of user data. SMS has also opened up GSM PLMN for support of telematics. For example, with a reduced GSM user equipment, a vending machine can become a short message sending entity to send a message to the vendor when a specific supply is needed.
SMS is defined with a store-and-forward mechanism. In this way the message is saved in case the addressee is not reachable and is later delivered based on availability. A subscriber must subscribe to this service, and it is provisioned in the subscriber's profile in HLR. The SMS-GMSC is the gateway to a GSM PLMN for SM delivery addressed in the PLMN. The SMS-GMSC interrogates the HLR to locate the subscriber. The interrogation protocol is a generic protocol used also by the GSM call control procedures for locating a called party. The HLR informs about the current location in terms of MSC/VLR, which is used by the SMS-GMSC for eventual delivery of the SM to the MS. In case the MS is not reachable, the HLR sends a response back to the SMS-GMSC.
There is another type of SMS service called SMS broadcast, which is the only broadcast channel data service. As the name implies, the user terminal can only receive the data broadcasted from the network. This service transports data on a specially defined broadcast channel, CBCH, over the air interface. This service is also limited to a short text string based on the carrying capacity of the CBCH. This service was anticipated to be used by the broadcast data applications, such as traffic reports and weather alerts. This service didn't get much attention from service providers because it didn't provide a good revenue generation model.
SMS point-to-point (SMS p-p) is a dedicated service between two users. GSM has defined two teleservices for SMS: SMS-MO (mobile origination), and SMS-MT (mobile termination). Using this service, a user sends a short string of alphanumeric characters to another user. SMS can also be used by the network operators to notify a user about certain status (e.g., number of messages waiting in voice mail). SMS is based on the concept that the signaling channel capacity can be utilized for carrying a few bytes of user data. SMS has also opened up GSM PLMN for support of telematics. For example, with a reduced GSM user equipment, a vending machine can become a short message sending entity to send a message to the vendor when a specific supply is needed.
SMS is defined with a store-and-forward mechanism. In this way the message is saved in case the addressee is not reachable and is later delivered based on availability. A subscriber must subscribe to this service, and it is provisioned in the subscriber's profile in HLR. The SMS-GMSC is the gateway to a GSM PLMN for SM delivery addressed in the PLMN. The SMS-GMSC interrogates the HLR to locate the subscriber. The interrogation protocol is a generic protocol used also by the GSM call control procedures for locating a called party. The HLR informs about the current location in terms of MSC/VLR, which is used by the SMS-GMSC for eventual delivery of the SM to the MS. In case the MS is not reachable, the HLR sends a response back to the SMS-GMSC.
High-Speed Circuit Switched Data
The HSCSD feature allows subscribers to access higher data rates with multiple TCH/Fs . HSCSD has defined mechanisms to make efficient and flexible use of radio resources for HSCSD. Combining/splitting functionality is defined in the IWF and terminal to separate a data stream into n TCH/F, where n ranges from 1 to 8. These n TCH/Fs, carrying a data stream, are referred to as HSCSD channels. The HSCSD channels carry the substreams as if they were independent of each other. However, the HSCSD channels, serving one stream, are controlled as one radio link. Any cellular operation (e.g., handover), treats the HSCSD channels of one stream as a single entity.
Before HSCSD, the air interface user rate in the original GSM data transmission was limited to 9.6 Kbps. The HSCSD made it possible to have user data rates up to 57.6 Kbps, with the same GSM RF equipment. The data rate is limited by the per-channel capacity on the A interface, which is 64 Kbps.To carry more than 64 Kbps, another split/combine function has to be defined and implemented for the terrestrial circuits on the terminating party. This is not realistic and not needed for circuit switched data.HSCSD doesn't impose any new requirement for the interconnection with PSTN, ISDN, CSPDN, and PSPDN. The subscriber uses general bearer services as defined in GSM TS 02 series, and the HLR stores the bearer capability information as part of the service profile.
HSCSD serves both transparent and nontransparent connections. In transparent data transmission, the data frames on the HSCSD channels carry data substream numbers to retain the order of transmission between the split/combine functions. Between these functions, channel internal multiframing is also used in order to increase the tolerance against inter-channel transmission delays. A transparent connection may request a data rate that is not a multiple of rates provided by one TCH/F. In such a case the data bits in the nth TCH/F need to be padded with fill bits. In nontransparent connection, the RLP and L2R are modified to support multiple parallel TCH/Fs instead of only one TCH/F. Also, the RLP frame sequence number range is increased to accommodate the enlarged data transmission rate.
HSCSD provides both symmetric and asymmetric connection setup. In the symmetric connections, the number of HSCSD channels is same in both uplink and downlink directions. In asymmetric connections, the number of HSCSD channels is different. The network usually allocates asymmetric connections when the desired air interface user rate requirement cannot be met using a symmetric configuration. The network in this case gives priority to fulfilling the air interface user rate requirement in the downlink direction. This is in consideration that the downlink bandwidth is needed more than the uplink bandwidth for most data applications. Note that the asymmetric connections are only given for nontransparent HSCSD.
Before HSCSD, the air interface user rate in the original GSM data transmission was limited to 9.6 Kbps. The HSCSD made it possible to have user data rates up to 57.6 Kbps, with the same GSM RF equipment. The data rate is limited by the per-channel capacity on the A interface, which is 64 Kbps.To carry more than 64 Kbps, another split/combine function has to be defined and implemented for the terrestrial circuits on the terminating party. This is not realistic and not needed for circuit switched data.HSCSD doesn't impose any new requirement for the interconnection with PSTN, ISDN, CSPDN, and PSPDN. The subscriber uses general bearer services as defined in GSM TS 02 series, and the HLR stores the bearer capability information as part of the service profile.
HSCSD serves both transparent and nontransparent connections. In transparent data transmission, the data frames on the HSCSD channels carry data substream numbers to retain the order of transmission between the split/combine functions. Between these functions, channel internal multiframing is also used in order to increase the tolerance against inter-channel transmission delays. A transparent connection may request a data rate that is not a multiple of rates provided by one TCH/F. In such a case the data bits in the nth TCH/F need to be padded with fill bits. In nontransparent connection, the RLP and L2R are modified to support multiple parallel TCH/Fs instead of only one TCH/F. Also, the RLP frame sequence number range is increased to accommodate the enlarged data transmission rate.
HSCSD provides both symmetric and asymmetric connection setup. In the symmetric connections, the number of HSCSD channels is same in both uplink and downlink directions. In asymmetric connections, the number of HSCSD channels is different. The network usually allocates asymmetric connections when the desired air interface user rate requirement cannot be met using a symmetric configuration. The network in this case gives priority to fulfilling the air interface user rate requirement in the downlink direction. This is in consideration that the downlink bandwidth is needed more than the uplink bandwidth for most data applications. Note that the asymmetric connections are only given for nontransparent HSCSD.
Fax Transmission
GSM technology provides two types of teleservices for fax: alternate speech/facsimile group 3 (TS 61) and automatic facsimile group 3 (TS 62). TS 61 is used when the user wants to switch between the voice call and the fax machine. It uses an in-call modification procedure via the user interface. The fax service can be provided on both transparent and nontransparent connections. Both mobile originated and terminated fax calls are supported. The bearer service information transfer mode for fax is circuit, duplex, synchronous, and symmetric.For GSM, the group 3 facsimile service is adapted from the fixed network specification defined in ITU-T F.160. This service specification is comprised of two parts: the control protocol described in ITU-T T.30, and the document transmission coding described in ITU-T T.4.
GSM terminal equipment can be connected to a two-wire basic fax machine with the use of the fax adapter function. The fax adapter function converts the analog signals coming from the two-wire fax machine into a serial digital stream having the ISDN-specific R interface as the output. This R interface output needs a standard synchronous TAF (GSM 07.03) to connect to the GSM MS. A personal computer (PC), emulating a fax machine, can be connected directly to a GSM phone with a commercially available PCMCIA fax card supporting GSM phones. In the PCMCIA fax card, the TAF and fax adapter functions are combined.
The MSC transfers the data link to the proper IWF. Different types of IWF are possible for the different type of transit networks. The transit network subsequently transports the fax information to the receiving fax machine. Both fax machines communicate with each other using the standard fax protocol defined in ITU-T T.30. It should be noted that depending on the implementation, the R reference point might not exist explicitly. In this case the LAPB protocol and consequently the LAPB entities operating across this interface may be omitted. L2RBOP and RLP protocol stacks are used at the radio interface.
As the fax data is synchronous, RA1' is used to transform the data rates supported on the air interface while adding some control bits. The air interface rate could be 3.6, 6, or 12 Kbps, depending on the bearer service subscribed by the fax user. The data is sent over the air with FEC. In the BSS, fax data is transformed into the intermediate rates of 8 or 16 Kbps by the RA1 function. The intermediate rate is transformed into an A interface data stream of 64 Kbps by the RA2 function. A similar view can be established for the transparent fax with the absence of L2R and RLP functions.
GSM terminal equipment can be connected to a two-wire basic fax machine with the use of the fax adapter function. The fax adapter function converts the analog signals coming from the two-wire fax machine into a serial digital stream having the ISDN-specific R interface as the output. This R interface output needs a standard synchronous TAF (GSM 07.03) to connect to the GSM MS. A personal computer (PC), emulating a fax machine, can be connected directly to a GSM phone with a commercially available PCMCIA fax card supporting GSM phones. In the PCMCIA fax card, the TAF and fax adapter functions are combined.
The MSC transfers the data link to the proper IWF. Different types of IWF are possible for the different type of transit networks. The transit network subsequently transports the fax information to the receiving fax machine. Both fax machines communicate with each other using the standard fax protocol defined in ITU-T T.30. It should be noted that depending on the implementation, the R reference point might not exist explicitly. In this case the LAPB protocol and consequently the LAPB entities operating across this interface may be omitted. L2RBOP and RLP protocol stacks are used at the radio interface.
As the fax data is synchronous, RA1' is used to transform the data rates supported on the air interface while adding some control bits. The air interface rate could be 3.6, 6, or 12 Kbps, depending on the bearer service subscribed by the fax user. The data is sent over the air with FEC. In the BSS, fax data is transformed into the intermediate rates of 8 or 16 Kbps by the RA1 function. The intermediate rate is transformed into an A interface data stream of 64 Kbps by the RA2 function. A similar view can be established for the transparent fax with the absence of L2R and RLP functions.
Traffic Channel Data Services
The basic idea in providing TCH data service is to provide a CS conduit for carrying data from the user through the GSM PLMN and vice versa. The conduits are composed of CS bearers in the network and the TCH over the air interface.The data path establishment procedure is very similar to the voice path establishment. There is also an IWF with the MSC, which serves as a gateway between data signals in the GSM PLMN and other networks, such as PSTN (public switched telephone network) and PSPDN (public switched packet data network). With a TCH-Full rate (TCH/F), the maximum effective data rate possible is 9.6 Kbps.
With a TCH-Half rate (TCH/H), the maximum data rate is 4.8 Kbps. The GSM PLMN also provides high-speed circuit switched data (HSCSD), which combines multiple TCH/Fs and can provide a maximum data rate of 56 Kbps.GSM provides transparent and nontransparent connection for the TCH data services. In the transparent connection, the data services see the path between the IWF and terminal as a constant rate conduit. The GSM PLMN doesn't intercept the data protocol and the data traffic. The radio interface doesn't do any extra processing to safeguard the data from errors. The transparent connection is usually suited for constant rate and fixed delay applications.
In the nontransparent connection, the data protocol and the traffic are intercepted in the GSM PLMN. The data are intercepted to provide reliable transport over the low-bandwidth and error-prone radio link. The GSM specifications have defined link-layer protocols, L2R and RLP, for this purpose. Example applications for nontransparent connections are X.25 LAP-B and character-mode protocols like X.28.
For carrying data through a GSM PLMN, a set of services is defined. These services, called bearer services and teleservices, allow different types of data applications to carry data through the GSM PLMN. We will discuss these services in the next section. The GSM PLMN also interconnects with ISDN, CSPDN, and PSPDN for transparent/nontransparent data services using an IWF. The GSM PLMN performs a set of functions so the data can be carried between the IWF and mobile terminal. These functions are mainly to adapt the data to the circuit switch nature of the transport and the radio nature of the air interface. In this section we will also review those functions.
With a TCH-Half rate (TCH/H), the maximum data rate is 4.8 Kbps. The GSM PLMN also provides high-speed circuit switched data (HSCSD), which combines multiple TCH/Fs and can provide a maximum data rate of 56 Kbps.GSM provides transparent and nontransparent connection for the TCH data services. In the transparent connection, the data services see the path between the IWF and terminal as a constant rate conduit. The GSM PLMN doesn't intercept the data protocol and the data traffic. The radio interface doesn't do any extra processing to safeguard the data from errors. The transparent connection is usually suited for constant rate and fixed delay applications.
In the nontransparent connection, the data protocol and the traffic are intercepted in the GSM PLMN. The data are intercepted to provide reliable transport over the low-bandwidth and error-prone radio link. The GSM specifications have defined link-layer protocols, L2R and RLP, for this purpose. Example applications for nontransparent connections are X.25 LAP-B and character-mode protocols like X.28.
For carrying data through a GSM PLMN, a set of services is defined. These services, called bearer services and teleservices, allow different types of data applications to carry data through the GSM PLMN. We will discuss these services in the next section. The GSM PLMN also interconnects with ISDN, CSPDN, and PSPDN for transparent/nontransparent data services using an IWF. The GSM PLMN performs a set of functions so the data can be carried between the IWF and mobile terminal. These functions are mainly to adapt the data to the circuit switch nature of the transport and the radio nature of the air interface. In this section we will also review those functions.
GSM (Global System for Mobile Communication)
GSM is a TDMA-based wireless communications system. Work on the GSM specifications started in the 1980s in Europe as a result of the capacity limits being experienced by analog networks such as NMT.The GSM 900 system uses two 25-MHz bands for the uplink and downlink, and within this spectrum 200-KHz channels are allocated. The uplink and downlink are separated by a 45-MHz spacing. GSM 1800 uses two 75-MHz bands for the uplink and downlink. Again 200-KHz channels are allocated within those bands and are separated by a 95-MHz spacing. The 1900-MHz systems use two 60-MHz bands for the uplink and downlink using 200-MHz channels within those bands and separated by 80-MHz spacing.
Europe felt the need for a common mobile telephony standard since different countries had differing analog networks, and as a result roaming of subscribers between these networks was not possible. CEPT (Conference European des Postes et Telecommunications) is a standardization arena in Europe. A new group called GSM (Groupe Special Mobile) was formed within CEPT in 1982 whose task was to specify a unique radio communication system for Europe at 900 MHz. The mobile station (MS) is the terminal (phone, PDA mobile unit) provided to the subscriber. It is essentially a GSM two-way radio that conforms to the air interface specifications.
The base station subsystem is functionally subdivided into the base station controller (BSC) and the base transceiver station (BTS). A single BSC normally controls a large number of BTSs. BTSs contain the radio equipment and are connected to cell site antennas. The BTS is essentially a layer two bridge if viewed from a high-level perspective. It provides an entry point for the subscribers who are present in the cell, allowing them to make or receive calls. Some of the base station functions are radio transmission in GSM format, use of frequency hopping techniques, coding and decoding of radio channels, and measurement of quality and received power on traffic channels.
GSM uses two databases, called the home location register (HLR) and the visitor location register (VLR). The HLR contains the subscriber's profile information (which is static) as well as the current location of the subscriber (i.e., it knows the reachability information of the subscriber). The VLR stores the current location or point of attachment to the network and the state of the mobile terminal. For mobile terminated calls, the HLR is the initial signaling contact point in the mobile network, whereas the VLR is the initial signaling contact when the call originates from the mobile
Europe felt the need for a common mobile telephony standard since different countries had differing analog networks, and as a result roaming of subscribers between these networks was not possible. CEPT (Conference European des Postes et Telecommunications) is a standardization arena in Europe. A new group called GSM (Groupe Special Mobile) was formed within CEPT in 1982 whose task was to specify a unique radio communication system for Europe at 900 MHz. The mobile station (MS) is the terminal (phone, PDA mobile unit) provided to the subscriber. It is essentially a GSM two-way radio that conforms to the air interface specifications.
The base station subsystem is functionally subdivided into the base station controller (BSC) and the base transceiver station (BTS). A single BSC normally controls a large number of BTSs. BTSs contain the radio equipment and are connected to cell site antennas. The BTS is essentially a layer two bridge if viewed from a high-level perspective. It provides an entry point for the subscribers who are present in the cell, allowing them to make or receive calls. Some of the base station functions are radio transmission in GSM format, use of frequency hopping techniques, coding and decoding of radio channels, and measurement of quality and received power on traffic channels.
GSM uses two databases, called the home location register (HLR) and the visitor location register (VLR). The HLR contains the subscriber's profile information (which is static) as well as the current location of the subscriber (i.e., it knows the reachability information of the subscriber). The VLR stores the current location or point of attachment to the network and the state of the mobile terminal. For mobile terminated calls, the HLR is the initial signaling contact point in the mobile network, whereas the VLR is the initial signaling contact when the call originates from the mobile
AMPS
First-generation mobile networks are analog systems. Some of the more widely deployed first-generation networks include AMPS and NMT. In this section we focus the discussion on AMPS.The Advanced Mobile Phone Service (AMPS) is in wide use even today, almost 25 years after it was introduced. AMPS was conceived by Bell Labs in the 1970s, and improvements in the form of digital AMPS (D-AMPS) were made in the late 1980s. The AMPS air interface is specified in EIA/TIA-553. AMPS is based on FDMA.
The FCC allocated a total of 50 MHz (25 MHz on the A side and B side) in the 800-MHz spectrum for AMPS. Each voice channel is allocated a 30-KHz portion of the bandwidth within the AMPS frequency allocations. Because each carrier has 25 MHz of spectrum, this provides a total of 832 (25 MHz/30 KHz) cellular channels (forward and reverse). However, since the same frequency cannot be used in adjacent cells, the 416 duplex channels are a theoretical maximum (actual number of valid voice channels equals 312). AMPS uses the seven-cell frequency reuse method. Control channels are used to set up and clear calls as well as other control messages. Each band (25 MHz) contains 21 control channels.
When a mobile station is not in session, it must monitor designated control channels. It tunes and locks into the strongest channel to receive system information. The forward control channel (FOCC) is a data stream from the base station to the mobile, and the reverse control channel (RECC) is from the mobile to the base station. Voice conversation is carried over the forward voice channel (FVC) and the reverse voice channel (RVC).The ESN for a mobile is a 32-bit number that uniquely identifies a mobile and is set up by the mobile manufacturer. System IDs (SIDs) are 15-bit binary numbers that are assigned to cellular systems. One of the uses of the SID is to determine a home network from a roaming network.
The MIN is a 34-bit number that is derived from the mobile terminal's 10-digit telephone number.The network utilizes the IS-41 protocol for mobility and authentication procedures. The MSC provides the capability for call processing, and the HLR and VLRs keep track of the mobile as it moves. The mobile terminal is responsible for updating its location as it moves in the cellular network. Data services in AMPS are straightforward and analogous to dial-up networking. Because AMPS is an analog technology, it is possible to make use of standard modems directly with AMPS. Data rates are at a maximum of 14.4 Kbps irrespective of the modem protocol (v.90 or others).
The FCC allocated a total of 50 MHz (25 MHz on the A side and B side) in the 800-MHz spectrum for AMPS. Each voice channel is allocated a 30-KHz portion of the bandwidth within the AMPS frequency allocations. Because each carrier has 25 MHz of spectrum, this provides a total of 832 (25 MHz/30 KHz) cellular channels (forward and reverse). However, since the same frequency cannot be used in adjacent cells, the 416 duplex channels are a theoretical maximum (actual number of valid voice channels equals 312). AMPS uses the seven-cell frequency reuse method. Control channels are used to set up and clear calls as well as other control messages. Each band (25 MHz) contains 21 control channels.
When a mobile station is not in session, it must monitor designated control channels. It tunes and locks into the strongest channel to receive system information. The forward control channel (FOCC) is a data stream from the base station to the mobile, and the reverse control channel (RECC) is from the mobile to the base station. Voice conversation is carried over the forward voice channel (FVC) and the reverse voice channel (RVC).The ESN for a mobile is a 32-bit number that uniquely identifies a mobile and is set up by the mobile manufacturer. System IDs (SIDs) are 15-bit binary numbers that are assigned to cellular systems. One of the uses of the SID is to determine a home network from a roaming network.
The MIN is a 34-bit number that is derived from the mobile terminal's 10-digit telephone number.The network utilizes the IS-41 protocol for mobility and authentication procedures. The MSC provides the capability for call processing, and the HLR and VLRs keep track of the mobile as it moves. The mobile terminal is responsible for updating its location as it moves in the cellular network. Data services in AMPS are straightforward and analogous to dial-up networking. Because AMPS is an analog technology, it is possible to make use of standard modems directly with AMPS. Data rates are at a maximum of 14.4 Kbps irrespective of the modem protocol (v.90 or others).
Radio Access Network
The radio access network comprises of the base transceiver stations (BTSs) and the controller element, which is called the base station controller (BSC). The BTSs are basically the radio elements (RF equipment) on the network side. Mobile terminals connect to the network via the BTSs. The BTS transmits system information over channels defined for broadcastting network specific information, and mobile stations tune in to these channels before performing access functions. A BTS is connected to a cell site, which hosts antennas atop towers or buildings. Cell sites can be of type macro, micro, or pico depending on the coverage radius. The size of a cell site is dependent on the transmit power level of the BTS.
The radio access network is the largest component of the mobile network, and a large number of base stations and cell sites are provisioned in order to provide coverage. Nationwide coverage of mobile networks requires the deployment of thousands of BTSs (coverage of the United States for example). The BTSs provide the channels for use on a dynamic basis to subscribers. Traffic and control channels are defined for the air interfaces depending on the type of technology used. The BTSs are controlled by the base station controller.
So from a relationship perspective, a single BSC controls many BTSs. The BSC is responsible for managing the radio resources at the BTSs. The BSC assigns channels to subscribers on a need basis. In addition, it is constantly aware of a mobile station's location and the state that it is in. It measures the signal strength (with the assistance of the BTS and the MS) and makes handoff decisions. In the case of CDMA networks, BSCs are also responsible for performing the macro-diversity-combining function required in spread spectrum systems. In addition, the speech coding function may be incorporated into the BSC in some cases.BSCs are connected to the BTSs over a wireline network using T1s and E1s. T1s and E1s are physical layer transmission technologies that are widely deployed by telecom operators. T1 is able to multiplex voice and data together in 24 user slots within a frame, as compared to E1, which has 30 user slots within each frame. Microwave links are also used for these connections. BTSs are normally deployed at the cell sites itself and hence are spread out geographically. The network connecting the BTSs to the BSC is referred to as a backhaul network. The BSC is normally at a central location such as a central office. The cost of connecting a large number of BTSs to the BSC is a major expense in radio networks.
The radio access network is the largest component of the mobile network, and a large number of base stations and cell sites are provisioned in order to provide coverage. Nationwide coverage of mobile networks requires the deployment of thousands of BTSs (coverage of the United States for example). The BTSs provide the channels for use on a dynamic basis to subscribers. Traffic and control channels are defined for the air interfaces depending on the type of technology used. The BTSs are controlled by the base station controller.
So from a relationship perspective, a single BSC controls many BTSs. The BSC is responsible for managing the radio resources at the BTSs. The BSC assigns channels to subscribers on a need basis. In addition, it is constantly aware of a mobile station's location and the state that it is in. It measures the signal strength (with the assistance of the BTS and the MS) and makes handoff decisions. In the case of CDMA networks, BSCs are also responsible for performing the macro-diversity-combining function required in spread spectrum systems. In addition, the speech coding function may be incorporated into the BSC in some cases.BSCs are connected to the BTSs over a wireline network using T1s and E1s. T1s and E1s are physical layer transmission technologies that are widely deployed by telecom operators. T1 is able to multiplex voice and data together in 24 user slots within a frame, as compared to E1, which has 30 user slots within each frame. Microwave links are also used for these connections. BTSs are normally deployed at the cell sites itself and hence are spread out geographically. The network connecting the BTSs to the BSC is referred to as a backhaul network. The BSC is normally at a central location such as a central office. The cost of connecting a large number of BTSs to the BSC is a major expense in radio networks.
Telnet/FTP
Telnet and FTP are two very commonly used application-layer protocols on the Internet. They have been around for over 20 years now.Telnet is an application-layer protocol and allows a user to connect to an account on another remote mechine. A client program on one machine can connect with a server program running on another machine using this protocol. Users utilizing Telnet interact with the remote machine in the same way as they would with a local machine. Telnet was one of the earliest protocols and in the early days was used primarily to allow users in one location to access accounts or machines in another location.
The default port (reserved by IANA) that the telnet client connects to on the server side is port 23. The client/server TCP connection is maintained throughout the telnet session. Since telnet can work across different platforms, telnet assumes that the hosts run a general network virtual terminal, which is a simple character device with a keyboard and printer. Data typed by a user on the keyboard are transmitted to the remote server, and the received data from the server are output to the printer.
In order to differentiate between a telnet control message and user data, each control message is preceded with a special octet, eight bits of 1s. Initial control messages during a telnet setup indicate the capabilities of the two endpoints to each other. After this is completed, the server requests an ID and password for logging in. The user types in his or her ID and password, and this is transferred to the server over the TCP connection. Once authenticated at the server, the connection is opened and data start to flow in both directions.
The File Transfer Protocol (FTP), as the name indicates, is used to download or copy files between remote machines connected via an IP network. FTP is also a client/server protocol. One of the interesting aspects of FTP is that it uses separate TCP connections to send control messages and to send data. The default port assigned by IANA for FTP on an FTP server is 21. FTP also uses TCP as the underlying transport protocol. A file is transmitted as a stream of bytes, and the closing of the TCP connection setup indicates the completion of the transmission. The control connection persists across multiple file transfers. But every file transfer requires a separate data connection. FTP is in the process of being enhanced in the IETF by a working group known as FTPext.
The default port (reserved by IANA) that the telnet client connects to on the server side is port 23. The client/server TCP connection is maintained throughout the telnet session. Since telnet can work across different platforms, telnet assumes that the hosts run a general network virtual terminal, which is a simple character device with a keyboard and printer. Data typed by a user on the keyboard are transmitted to the remote server, and the received data from the server are output to the printer.
In order to differentiate between a telnet control message and user data, each control message is preceded with a special octet, eight bits of 1s. Initial control messages during a telnet setup indicate the capabilities of the two endpoints to each other. After this is completed, the server requests an ID and password for logging in. The user types in his or her ID and password, and this is transferred to the server over the TCP connection. Once authenticated at the server, the connection is opened and data start to flow in both directions.
The File Transfer Protocol (FTP), as the name indicates, is used to download or copy files between remote machines connected via an IP network. FTP is also a client/server protocol. One of the interesting aspects of FTP is that it uses separate TCP connections to send control messages and to send data. The default port assigned by IANA for FTP on an FTP server is 21. FTP also uses TCP as the underlying transport protocol. A file is transmitted as a stream of bytes, and the closing of the TCP connection setup indicates the completion of the transmission. The control connection persists across multiple file transfers. But every file transfer requires a separate data connection. FTP is in the process of being enhanced in the IETF by a working group known as FTPext.
Push To Talk
The Push to Talk feature on cell phones is just like using a walkie-talkie but over the cellular network. One major benefit of using the Push to Talk feature over actually calling someone is that Push to Talk connects instantaneously. Push to Talk or walkie-talkie communication only provides half duplex communications.Half duplex communications means only one party can talk at any moment while others listen. For example, when you call someone and you are having a conversation, both parties can listen and talk simultaneously and have full duplex communication. This is not the case with Push to Talk, with Push to Talk one person connects with another person or a group and speaks then those who were listening can respond back, but not at the same time simultaneously.
Push to Talk also saves a great amount of time when communicating. Imagine you have to coordinate plans between 5 different people and you call each one, dial their number, wait for the call, letting it ring a few times and finally communicating where with Push to Talk, you can connect instantaneously with just a push of a button and communicate.Nextel originally started the walkie-talkie or Push to Talk service and all their cell phones came with this feature built in. Later on, other carriers such as Cingular/AT&T and Verizon Wireless also started implementing and selling this useful feature.
The major difference between all these carriers is all Nextel devices had this feature whereas with other carriers only certain phones were Push to Talk enabled, which meant in order for Verizon or Cingular/AT&T customers to use Push to Talk communication, other customers had to have a device with this capability built in. For this reason, Push to Talk never really got as popular with other carriers as it did and is with Nextel/Sprint now.When looking to purchase a cell phone with this feature, look for Push to Talk/PTT/Walkie-Talkie features in the phone's description or feature list. In addition, expect to pay for an extra add-on plan to use the Push to Talk feature.
PTT offers "walkie-talkie" type functionality whereas the user presses a button to connect directly to the other party in a series of one-way voice communications back and forth. PTT PoC or Push to Talk over Cellular is a feature similar to walkie-talkie that is provided over a cellular phone network. A typical Push to Talk connection connects almost instantly. One significant advantage of PoC is allowing a single person to reach an active talk group at a button press, thus users no longer need to make several calls to coordinate with a group. Just like Walkie. Push-to-talk calls are half duplex communications—while one person speaks,the other(s)listen(s).PTT service is supported only between parties on the same mobile carrier service, and users with different carriers will be unable to transmit to each other by PTT.
Push to Talk also saves a great amount of time when communicating. Imagine you have to coordinate plans between 5 different people and you call each one, dial their number, wait for the call, letting it ring a few times and finally communicating where with Push to Talk, you can connect instantaneously with just a push of a button and communicate.Nextel originally started the walkie-talkie or Push to Talk service and all their cell phones came with this feature built in. Later on, other carriers such as Cingular/AT&T and Verizon Wireless also started implementing and selling this useful feature.
The major difference between all these carriers is all Nextel devices had this feature whereas with other carriers only certain phones were Push to Talk enabled, which meant in order for Verizon or Cingular/AT&T customers to use Push to Talk communication, other customers had to have a device with this capability built in. For this reason, Push to Talk never really got as popular with other carriers as it did and is with Nextel/Sprint now.When looking to purchase a cell phone with this feature, look for Push to Talk/PTT/Walkie-Talkie features in the phone's description or feature list. In addition, expect to pay for an extra add-on plan to use the Push to Talk feature.
PTT offers "walkie-talkie" type functionality whereas the user presses a button to connect directly to the other party in a series of one-way voice communications back and forth. PTT PoC or Push to Talk over Cellular is a feature similar to walkie-talkie that is provided over a cellular phone network. A typical Push to Talk connection connects almost instantly. One significant advantage of PoC is allowing a single person to reach an active talk group at a button press, thus users no longer need to make several calls to coordinate with a group. Just like Walkie. Push-to-talk calls are half duplex communications—while one person speaks,the other(s)listen(s).PTT service is supported only between parties on the same mobile carrier service, and users with different carriers will be unable to transmit to each other by PTT.
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