Suppose Host A sends 6 consecutive segments to Host B. Suppose the 1

st

segment is lost (when

transmitted for the first time) and there is no further loss. Suppose that the sequence number starts

from 1 and increments by 1 per segment. Further suppose that under Go-Back-N (GBN) or Selective-

Repeat (SR) protocol, the acknowledgement number is the sequence number of the segment it

acknowledges (initially 0), and under TCP, the acknowledgement number is the sequence number of the

next segment it expects. In the case of TCP, suppose that the sender uses fast retransmission, and the

receiver buffers out-of-order segments.

a) Under each of GBN, SR, and TCP: How many segments will Host A send in total? How many ACKs

will Host B send in total?

b) Give the sequence number of each segment sent by A, and the acknowledgement number of

each ACK sent by B, under each protocol.

c)

Suppose that the timeout values of all three protocols are longer than the time to send 6

segments and receive their ACKs (if not lost). Which protocol delivers all the segments fastest?

Why?