Explain the difference between the GobackN and Selective Rep

Explain the difference between the Go-back-N and Selective Repeat protocol. Explain the following:

a. Does this GBN protocol have a time for each unacknowledged packet? Explain

b. When a timer expires, what happens for the GBN?

c. Does the Selective Repeat protocol have a timer for each unacknowledged packet? Explain

d. When an acknowledgement arrives for the oldest unacknowledged packet what happens with Selective Repeat?

Solution

Both are basically error control protocols i.e they detect error and control it. The difference lies in the name itself \'Go-back-N\' it means it will back and retransmits all the frmaes which lies after the frame which was damaged or lost where in contrary to it \'Selective Repeat Protocol\' the name says Selective so it works on selection i.e. it will only retransmits the selected frame which got lost.

a) Go Back N protocol doesn\'t have timer for each packet, it maintains a single timer and no need to maintain timer for each packet.

b) When the timer expires, it resend all the packets for those it hasn\'t received ACK.