Mumbai University > Information Technology > Sem4 > CN

Marks: 5M

Year: Dec 2016

The glue that holds the whole Internet together is the network layer protocol,

IP (Internet Protocol)

• Communication in the Internet works as follows. The transport layer takes data streams and breaks them up so that they may be sent as IP packets. In theory, packets can be up to 64 KB each, but in practice they are usually not more than 1500 bytes (so they fit in one Ethernet frame).
• IP routers forward each packet through the Internet, along a path from one router to the next, until the destination is reached.
• At the destination, the network layer hands the data to the transport layer, which gives it to the receiving process. When all the pieces finally get to the destination machine, they are reassembled by the network layer into the original datagram. - This datagram is then handed to the transport layer.
• In the example of Fig. above, a packet originating at a host on the home network has to traverse four networks and a large number of IP routers before even getting to the company network on which the destination host is located. This is not unusual in practice, and there are many longer paths. There is also much redundant connectivity in the Internet, with backbones and ISPs connecting to each other in multiple locations. This means that there are many possible paths between two hosts. It is the job of the IP routing protocols to decide which paths to use.