Specifications

2.2 The TCP/IP protocol.

TCP/IP stands for Transmission Control Protocol/Internet Protocol. It is frequently

referred to as a “stack” because of the relation to the layers through which all the data

must pass at both client and server ends of a data exchange. These layers refer to the

different protocol implementation at different layers in the design as shown in figure 1.

Figure 1 The network layers [1]

On the left is the OSI model that was developed to standardise the layer implementation

of network communication. Each layer has its own function that works abstractly from

the next layer. Currently the OSI model is not used very much because the TCP/IP

model has become much more popular. In the TCP model the data link and physical

layers are combined to form the network layer. This layer looks after the physical bit

switching of the hardware and reliability issues, such as error checking and framing of

data. The network layer is called the IP layer or the internet protocol layer. This layer

handles the routing of packets; getting the IP packet from its source to the requested IP

address across the network. The transportation layer can be either TCP or UDP and

refers to the control of how messages are sent between the senders and receivers. TCP

allows for the message to be split into packets and then sent separately across the

network and manage the packets so that they are put back together in the correct order.

TCP is connection based so that before packets are sent over the network it is

established whether the receiver is ready and a virtual link is made between the two.

The application layer is the program that the user develops on top of the TCP layer. The

program passes messages to the TCP layer which inturn sends it the IP layer and then

the network layer. The data is then sent over the network and the receiver performs the

same operation in reverse.