Problem 2

Question 1 (6 points)
  • 1.5 point for each subnet.
  • If an allocated IP prefix is not minimal (but does not overlap with any other), the student gets 1 point for that prefix.
  • If an allocated IP prefix overlaps with another one, no points for that prefix.
Question 2 (8 points)
  • 1 points per correct entry.
  • No points if an entry has incorrect src/dst MAC/IP or incorrect application/purpose.
  • If an entry has incorrect transport protocol or src/dst port number, half the points.
  • If an entry does not specify the correct interface of the router for the src/dst MAC/IP and used the router's name instead, 0.75 points.
Question 3 (3 points)
  • 1 point for packet 3 (0.5 for correct prefix and 0.5 for correct protocol).
  • 1 point for packets 4, 6, 8 (0.5 for correct prefix and 0.5 for correct protocol).
  • 1 point for packets 5, 7 (0.5 for correct prefix and 0.5 for correct protocol: BGP or Dijkstra).
  • Both inter-domain (intra-domain) routing protocol or BGP (Dijkstra) are considered correct answers for the protocol.
  • If for a prefix, at least one correct packet number is listed but not all, 0.75 points out of 1. 
Question 4 (2 points)
  • 1 point for packets 5, 7 (0.5 for correct prefix and 0.5 for correct protocol)
  • 1 point for packets 6, 8 (0.5 for correct prefix and 0.5 for correct protocol)
  • Both inter-domain (intra-domain) routing protocol or BGP (Bellman-Ford) are considered correct answers for the protocol.
  • For each prefix, if at least one correct packet number is listed but not all, 0.75 points out of 1. 
Question 5 (10 points):
(a)
  • 2 points for correct table entries.
(b)
  • 4 points for correct use of of Poisoned Reverse.
  • 4 points for basic Bellman-Ford operations: propagation of route information and computation of the new route costs.

Problem 3

Question 1 (3 points)
  • 1 point for transmission rate (the lowest transmission rate of the links along the path) with proper justification.
  • 1 point for Bob’s TCP receive buffer with proper justification.
  • 1 point for propagation delay with proper justification.
Question 2 (7 points)
  • 2 points for correctly identifying the lost segment. 
  • 1.5 for the congestion window:
    • 0.5 for properly increasing cwnd before timeout
    • 0.5 for properly sending segments according to the cwnd (i.e. understanding you need to move the window on new ACKs)
    • 0.5 for setting cwnd to 1 after the timeout
  • 1 point for slow start threshold (0.5 for threshold before the timeout and 0.5 for after the timeout)
  • 1 point for congestion algorithm state (SS v.s. CA)
  • 1 point for SEQ and ACK (0.5 for correctly using duplicate ACKs)
  • 0.5 for showing the timeout.
Question 3 (6 points)
  • 1 point for SEQ and ACKs
  • 2.5 points for the actions when third duplicate ACK arrives
    • 0.5 for retransmitting the correct lost segment
    • 0.5 for ssthreshold = cwnd/2
    • 0.75 for cwnd = ssthreshold + 3
    • 0.75 for fast recovery as congestion control state
  • 1 point for increasing the cwnd by 1 when the 4th and 5th duplicate ACK arrives.
  • 1.5 point for the actions when a new ACK arrives
    • 0.75 for cwnd = ssthreshold 
    • 0.75 for congestion avoidance as a new congestion control state.

Last modified: Friday, 9 February 2024, 11:41