Information Technology Reference
In-Depth Information
23
TCP/IP
23.1 Introduction
Networking technologies such as Ethernet, Token Ring and FDDI provide a data link layer
function; that is, they allow a reliable connection between one node and another on the same
network. They do not provide internetworking where data can be transferred from one net-
work to another or from one network segment to another. For data to be transmitted across a
network requires an addressing structure which is read by a bridge, gateway and router. The
interconnection of networks is known as internetworking (or an internet). Each part of an
internet is a subnetwork (or subnet). Transmission control protocol (TCP) and Internet proto-
col (IP) are a pair of protocols that allow one subnet to communicate with another. A proto-
col is a set of rules that allows the orderly exchange of information. The IP part corresponds
to the network layer of the OSI model and the TCP part to the transport layer. Their opera-
tion is transparent to the physical and data link layers and can thus be used on ethernet, FDDI
or token ring networks. This is illustrated in Figure 23.1. The address of the data link layer
corresponds to the physical address of the node, such as the MAC address (in Ethernet and
Token Ring) or the telephone number (for a modem connection). The IP address is assigned
to each node on the Internet. It is used to identify the location of the network and any sub-
nets.
TCP/IP was originally developed by the US Defense Advanced Research Projects
Agency (DARPA). Their objective was to connect a number of universities and other re-
search establishments to DARPA. The resultant internet is now known as the Internet. It has
since outgrown this application and many commercial organizations now connect to the
Internet. The Internet uses TCP/IP to transfer data. Each node on the Internet is assigned a
unique network address, called an IP address. Note that any organisation can have its own
internets, but if it is to connect to the Internet then the addresses must conform to the Internet
addressing format.
Transport
TCP
Network
IP
Ethernet/
Token Ring/
FDDI/
ISDN
Data link
Physical
Figure 23.1
TCP/IP and the OSI model
