The Transmission Control Protocol/Internet Protocol (TCP/IP) originated in the 1970’s.  It was initially developed by the Department of Defence (DOD) in an attempt to connect a number of different networks Today however it is more commonly used as a standard communication protocol used in a number of networks  the most common of which is the Internet.

FIGURE 2

As it is depicted in Figure 2 above, the TCP/IP model itself consists of four layers and each layer is responsible for performing prescribed functions which will be discussed in detail below:

Application Layer  -  This layer is basically concerned with defining the protocols.  It consists of application programs and user interfaces. In practice it works by sending an unbroken "data stream" to the Transport layer .  At this stage the stream is broken into packets , each of which is "framed" with a TCP header (which contains the sender's and recipient's addresses and error checking information).  According to writers such as Buchanan it supports a number of protocols such as" SMTP, FTP and Telnet". (Buchanan. W, "Distributed Systems and Networks", McGraw- Hill, 2000)

Transport Layer  -    This layer is responsible for providing communication session management between host computers.  Generally speaking it defines the level of service and status of the connection used when transporting the data.  The main protocols that are used in this layer include TCP, UDP and RTP.

Internet Layer - This layer  is basically concerned with the Packaging of data.  Here the data is packaged into IP datagram's. which contain the source and destination address information. This is what is used to forward the datagram's between hosts and across networks and the,  main protocols used in this layer are IP, ICMP, ARP as well as RARP.

Network Interface Layer - This layer is responsible for specifying how the data will be sent through the network physically.  This includes assessing "how bits are electrically signalled by the hardware devices that interface directly with a network medium" (Croucher P, "Communications and Networks", 1999 British Library publication).  These devices generally include the types of caballing used such as the coaxial cable or the twisted pair copper wire.   Typical examples of protocols used throughout this layer are the "Token Ring", "Ethernet" and FDDI.

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