data is originated from one user and have to send to another user,while sending the data it has to pass through internet and has to follow certain protocol.you have already know about internet model and it's various layer.
data ha to pass through them. all the other queries of you is only a part of the process that has to follow. the data length are variable and it can't be send in a whole. so it has to break down. the data is first has to break down in segments at transport layer. after that segments will also break down or wrapped into packets at network layer and then it will be broken down in frames at data link layer. so that is the whole process and at the destination layer it has to go reverse of the above process.
Oct 20, 2013