The Internet

Today an estimated 15.7% of the world population has access to the Internet with the
highest concentration in North America (68.6%), Oceania/Australia (52.6%) and Europe
(36.1%).[48] In terms of broadband access, countries such as Iceland (26.7%), South
Korea (25.4%) and the Netherlands (25.3%) lead the world.The nature of computer network communication lends itself to a layered approach where individual protocols in the protocol stack run largely independently of other protocols. This allows lower-level protocols to be customized for the network situation while not changing the way higher-level protocols operate. A practical example of why this important is because it allows an Internet browser to run the same code regardless of whether the computer it is running on is connected to the Internet through an Ethernet or Wi-Fi connection. Protocols are often talked about in terms of their place in the OSI
reference model — a model that emerged in 1983 as the first step in a doomed attempt to
build a universally adopted networking protocol suite.

The model itself is outlined in the picture to the right. It is important to note that the Internet’s protocol suite, like many modern protocol suites, does not rigidly follow this model but can still be talked about in the context of this model. For the Internet, the physical medium and data link protocol can vary several times as packets travel between client nodes. Though it is likely that the majority of the distance travelled will be using the Asynchronous Transfer Mode (ATM) data link protocol across optical fibre this is in no way guaranteed. A connection may also encounter data link protocols such as Ethernet, Wi-Fi and the Point-to-Point Protocol (PPP) and physical
media such as twisted-pair cables and free space.


At the network layer things become standardized with the Internet Protocol (IP) being
adopted for logical addressing. For the world wide web, these “IP addresses” are derived
from the human readable form (e.g. 72.14.207.99 ) using the Domain Name System. At
the moment the most widely used version of the Internet Protocol is version four but a
move to version six is imminent. The main advantage of the new version is that it
supports 3.40 × 1038 addresses compared to 4.29 × 109 addresses. The new version also
adds support for enhanced security through IPSec as well as support for QoS
identifiers.


At the transport layer most communication adopts either the Transmission
Control Protocol (TCP) or the User Datagram Protocol (UDP). With TCP, packets are
retransmitted if they are lost and placed in order before they are presented to higher
layers (this ordering also allows duplicate packets to be eliminated). With UDP, packets
are not ordered or retransmitted if lost. Both TCP and UDP packets carry port numbers
with them to specify what application or process the packet should be handed to on the
client’s computer. Because certain application-level protocols use certain ports,
network administrators can restrict Internet access by blocking or throttling traffic
destined for a particular port.