retagged by
588 views
3 votes
3 votes

Read the below mentioned statements:

  1. The size of the $TCP$ advertised window  never changes throughout the duration of the connection.
  2. With the Selective Repeat protocol (which uses selective acknowledgement) it is not possible for the sender to receive an $ACK$ for a packet that falls outside of its current window.
  3. With the GoBackN, it is possible for the sender to receive an $ACK$ for a packet that falls outside of its current window.


Which of the above statements is FALSE?

  1.   I and II
  2.   II only
  3.   II and III
  4.   I only
retagged by

1 Answer

Best answer
4 votes
4 votes

Statement I :  It is False. It is the size of the receiver's buffer that's never changed.

Receiving Window is the part of the receiver's buffer that's changing all the time depending on the processing capability at the receiver's side and the network traffic.

Statement II it is False.  it is possible for the sender to receive an ACK for a packet that falls outside of its current window.

For detail example see [1] . 

Statement III it is true, GBN uses cumulative acknowlegement. Imagine a scenario where ACK1 arrives AFTER ACK2.

Once the sender receives ACK2, it would know that both packet1 and 2 were received correctly. So it can remove packet1 and 2 from its window. Now if ACK1 arrives, then ACK1 actually falls outside the current window . 

Reference:

[1] http://www.cmlab.csie.ntu.edu.tw/~rod24574575/CN2015/homeworks/hw4_sol.pdf 

selected by
Answer:

Related questions

1 votes
1 votes
1 answer
2