i am not sure with tihs question. i will post it here along with my attempt:

the following scenario is regarding go back protocol n, with 3 bits for sequential numbering, assuming that the following occurs:

  1. the number in the receiving window is 2
  2. frames 0-5 are sent one after the other
  3. frame 4 is lost
  4. all of the other frames are received as they should.


a)among the frames 0-5 that were sent, how many of them transmitted into the network layer?

b)was a confirmation sent after the arrival of the 5th frame? if yes, write the number in the confirmation. if not, explain.

c)will the previous answers(to questions a,b) change if (3) was "frame one lost" instead of "frame 4 lost"?

my attempt:

a)i don't understand it. go back n protocol is used whenever the size of the receive windows is 1. regardless of that, since the receiver checks the number of each frame, and if one frame is lost, then the lost of frame is easily identifiable because the newly received frame is out of sequence.the receiver discards all the frames received, after the lost frame, and that is done after sending NAK.so because of that, 5 is discarded according to the details. however, since the number in the receiving window is 2, and data link layer requires one, then no frames will be transferred into the network layer.

b)as from the previous answer, since packet 4 is lost, the packets after it are discarded and no ACK is sent for the packets after it.

c)if they are sent one after the other, in order, so if frame 1 was lost then the others would've been discarded and no ACK would've been sent after it, so b) wouldn't have change. because the receiving windows is still 2, then still, none of the frames would've been passed to the network layer.

could you please check if what i did is correct? i tried my best to provide elaborated answers.

thank you very much


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