sender receive send pkt0 __________ receive pkt0 send ack0 send pkt1 __________r
ID: 3691381 • Letter: S
Question
sender receive
send pkt0 __________ receive pkt0
send ack0
send pkt1 __________receive pkt2
send ack1
send pkt2 _________×
send pkt3 ___________receive pkt3, ?
in the figure above, a sender sends some packets to a receiver. Upon receiving pkt3 :
a) What will be the action of the receiver, if it is using Go-Back-N method?
b ) What will be the action of the receiver, if it is using Selective repeat method?
c ) The sender waits after sending pkt3. What can you say about the window size of the sender?
Explanation / Answer
Answer for Question:
Go back N protocol will resend the unacknowledged or lost frames pkt2, and pkt3
Answer for Question 2:
Selective Repeat attempts to retransmit only those packets that are actually lost (due
to errors)
– Receiver must be able to accept packets out of order
– Since receiver must release packets to higher layer in order, the receiver must be able to
buffer some packets
Answer for Question 3:
Window size = N
– Sender cannot send packet i+N until it has received the ACK for packet i
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