Problem 2

Question 1 (4 points)
  • 0.5 point per correct packet.
  • 0.25 point for a packet that has correct source, destination, and role, but wrong src and or dst port number.
Question 2 (3 points)
  • 0.25 point for sending DNS request
  • 0.25 point for reading DNS response
  • 0.5 point for creating new TCP socket
  • 0.5 point for binding it
  • 0.5 point for connecting it
  • 0.25 point for sending HTTP request
  • 0.25 point for reading HTTP response
  • 0.5 point for saying something reasonable about reading the entire HTTP response correctly (e.g., read the headers in one call, compute how many more bytes you need to read in the next call)
Question 3 (3 points)
  • 0.5 point for DNS request’s transmission delay
  • 0.5 point for DNS request’s propagation delay
  • 0.5 point for DNS response’s transmission delay
  • 0.5 point for DNS response’s propagation delay
  • 0.5 point for TCP SYN propagation delay
  • 0.5 point for TCP SYN ACK propagation delay
  • OK if compute some transmission delay for SYN and SYN ACK
Question 4 (6 points)
  • 1 point for HTTP GET request’s transmission delay
  • 1 point for HTTP GET request’s propagation delay
  • 1 point for HTTP response’s transmission delay, 1st packet on 1st link
  • 1 point for HTTP response’s transmission delay, all packets over second link
  • 1 point for HTTP response’s transmission delay, last packet on last link
  • 1 point for HTTP response’s propagation delay
Question 5 (3 points)
  • 1 point for saying it’s position P2.
  • 1 point for saying it’s because there are more packets sent from the web server to Alice.
  • 1 point for mentioning queueing delay.
Question 6 (6 points)
  • 3 points for correct computation of max queuing delay per packet at a switch.
  • 3 points for multiplying max queuing delay by 100 or 101.
    • (1/3 points for multiplying max queuing delay by 200 or 202)
    • (1/3 points for multiplying max queuing delay by 100 or 101 AND incorrect computation of max queuing delay per packet at a switch)
    • (1/3 points for accounting for max queuing delay on both directions, server->Alice and Alice->server)
Question 7 (5 points)
  • 1 point for listing a correct hop.
  • 1.5 point for showing reasonable RTTs to each hop.
  • 0.5 point for justifying the RTTs.

Problem 3

Question 1 (0.5 point)
  • 0.25 for the MSS.
  • 0.25 for any reasonable justification.
Question 2 (0.5 point)
  • 0.25 for the window size.
  • 0.25 for any reasonable justification.
Question 3 (4 points)
  • 1 point for saying 5 was lost.
  • 1 point for justifying it.
  • 1 point for saying that 6,7,8 may have been lost.
  • 1 point for justifying it.
  • A correct diagram does count as justification.
Question 4 (4 points)
  • 0.5 point for saying ACK 5 was lost. 
  • 0.5 point for justifying it.
  • 0.5 point for saying ACK 6 and 7 were lost. 
  • 0.5 point for justifying it.
  • 0.5 point for saying ACK 8 was lost. 
  • 0.5 point for justifying it.
  • 0.5 point for saying that the ACKs for retransmitted 5, 6, and 7 may have been lost.
  • 0.5 point for justifying it.
  • A correct diagram does count as justification.
Question 5 (1 point)
  • 0.5 point for the RTT.
  • 0.5 point for any reasonable justification.
Question 6 (1 point)
  • 0.5 point for the timeout.
  • 0.5 point for any reasonable justification.
Question 7 (4 points)
  • 1 point for saying that A sends 900 bytes to B.
  • 0.5 point for saying we don’t have enough data to exactly compute.
  • 0.5 point for saying why.
  • 1 point for any reasonable approximation.
  • 1 point for a correct justification (of the reasonable approximation).


Last modified: Monday, 14 December 2020, 09:53