Working of TCP/IP

A collection of networks is called the Internet.

Each network that is a part of the internet is called a Sub-Network.

In order for the hosts present in the internet to communicate with each other each host must be given a unique address, called IP address. Also we need to specify the port address if the source as well as destination.

Suppose an application (process) with Port I at Host A, wishes to send message to another processes associated with Port 2 at Host B, the message at A is first handed over to TCP present on the transport layer which in turn passes the message down to internet layer. The IP in turn hands over the message down to the network access layer along with the instructions like how? When? And to whom? It should be sent.

In order for these things to happen the working of TCP/IP comes to play, the message should be arranged suitably.

a. The application while sending the message to TCP, it arranges the message as a block of data.

b. The TCP divides this block into a number of smaller pieces for manageability. It then adds control information to each piece called TCP header. Now this piece of message along with TCP header forms a Segment.

c. Next, each segment is handed over to IP. The IP now adds extra control information to each segment called IP header to form an IP Datagram.

d. Each IP diagram is then presented to network access layer which then appends another header to form a Packet or a Frame.

e. The frame is then transmitted across the sub network to reach the Rooter.

f. The Rooter removes the frame header and checks the IP header to determine the destination address.

g. The IP module present in the router forwards the diagram to the specified network

h. Upon receiving the data gram, the receiver would remove one header and passes the remainder on to the next higher layer until the original user data is delivered to the application.

Note: A block of data is exchanged between two layers is called a protocol data unit (PDU).

For example: Segment is the block of data that is PDU that is exchanged between the transport layer and internet layer.

The following diagram illustrates the TCP/IP concept.

TCP/IP Protocol