The Tradition of Sharing

Help your friends and juniors by posting answers to the questions that you know. Also post questions that are not available.

To start with, Sr2Jr’s first step is to reduce the expenses related to education. To achieve this goal Sr2Jr organized the textbook’s question and answers. Sr2Jr is community based and need your support to fill the question and answers. The question and answers posted will be available free of cost to all.

Computer Networking : A Top-Down Approach

Computer Networking : A Top-down Approach

James F. Kurose, Keith W. Ross
Transport Layer



Consider our motivation for correcting protocol rdt2.1. Show that the receiver, shown in Figure 3.57, when operating with the sender shown in Figure 3.11, can lead the sender and receiver to enter into a deadlock state, where each is waiting for an event that will never occur.


Consider the states of sender and receiver as follows:

Sender state as “wait for call 1 from above”.

Receiver state as “wait for 1 from below”.


  • Initially sender sends a packet with sequence number 1.
  • After sending the packet, the state of the sender will be “wait for ACK or NAK 1” (indicates that sender waits for acknowledgement ACK or NAK from receiver).
  • The receiver receives the packet 1 and sends the ACK.
  • After acknowledging the packet, the state of the receiver is “wait for 0 from below” (indicates that the receiver is waiting for packet 0).
  • Assume that sender receives the corrupted ACK sent by the receiver for packet 1.
  • Since the sender received the corrupted ACK, it transmits the packet 1 again.
  • The receiver sends a NAK as it received packet with sequence number 1 again instead of packet with sequence number 0.
  • The sender sends the packet with sequence number 1 again.
  • The receiver sends NAK again to sender.


Therefore, the sender repeats the sending packet with sequence number 1 and the receiver sends NAK again to sender. This raises a deadlock stage for both sender and the receiver.

1 0


Post the discussion to improve the above solution.