Windows Protocol

Sliding Windows Protocol are more robust and continue to function even under pathological conditions. When there is a need for transmitting data in both directions and the idea is to use the same circuit for data in both directions –then sliding windows protocol is that at any instant of time, the sender maintains a set of sequence number corresponding to frames it is permitted to send. These frames are said to fall.

Within the sending windows. Similarly, the receiver also maintains a receiving windows corresponding to the set of frames it is permitted to accept. The sender’s windows and the receiver’s windows need not have the same lower and upper limits or even have the same size. In some protocol they are fixed in size but in others they can glow or shrink as frames are sent and received.

In all sliding windows protocol, each out bound frame contains a sequence number, ranging from 0 upto some maximum. The maximum is usually 2n-1 so the sequence number fits nicely in an n-bit field. The stop-and-wait sliding windows protocol uses n=1, restricting the sequence number to 0 and 1, but more sophisticated versions can use arbitrary n.

Although sliding windows protocol give the data link layer more freedom about the order in which it may send and receive frames the protocol must deliver packets to the destination computer network layer in the same order that they were passed to the data link layer on the sending machine.