Computer  Science 826
                              Quiz 7           Name _______________________

1. The primary objective the "slow start" mechanism is to

   a. Ensure that the throughput        b. Prevent a fast sender from
      obtained doesn't exceed              overwhelming a slow receiver
      available bandwidth
   c. Prevent a rapid buildup of        d. All of the above apply
      packets at a bottleneck router       equally

2. When slow-start is being performed, each time a full congestion window
   of segments is sent and acked, the size of cwnd typically
   a. Increases by 1 byte               b. Increases by 1 * MSL
   c. Doubles                           d. Stays the same

3. Consider the following Slow_Start TCP exchange: (MSS = 1000)
                    Seq=   0, Len=1000, Ack=   0 --->
              <---  Seq=   0, Len=   0, Ack=1000
                    Seq=1000, Len=1000, Ack=   0 --->
                    Seq=2000, Len=1000, Ack=   0 --->
              <---  Seq=   0, Len=   0, Ack=2000
                    Seq=3000, Len=1000, Ack=   0 --->
                    Seq=4000, Len=1000, Ack=   0 --->
              <---  Seq=   0, Len=   0, Ack=3000
   How many more segments can be sent from left to right
   before the sender has to halt due to full cwnd

   a. none (already blocked)        b. 1
   c. 2                             d. 3

4. Suppose cwnd=5000, MSS=1000, slow start is being performed and
   an ack for 1 new segment is received.  What will the new value of cwnd?



5. Suppose cwnd=5000, MSS=1000, congestion avoidance is being performed and
   an ack for 1 new segment is received.  What will the new value of cwnd?
   (Ignore the BSD Bug/hack)



6. After a successful fast-retransmit and fast-recovery completes with
   an ack for new data the size of cwnd is:

   a. 1 segment                     b. about twice the size it was before
                                       the fast-retransmit / fast-recovery


   c. about 1/2 the size it was     d. about the same size it was before
      before the fast-retransmit       the fast retransmit / fast recovery.
      / fast-recovery


7. After a timeout the size of cwnd is:

   a. 1 segment                     b. about twice the size it was before
                                       the fast-retransmit / fast-recovery

   c. about 1/2 the size it was     d. about the same size it was before
      before the fast-retransmit       the fast retransmit / fast recovery.
      / fast-recovery


8. The main objective of Jacobson's new RTO estimator was to

   a. improve the long term estimation  b. improve the mean estimators
      of the mean response time.           ability to track short term
                                           changes in the true mean RTT.

   c. Weight the RTT estimator with
      a reasonable estimate of the
      variance.


9. Suppose MSS = 1000 bytes, cwnd = 8000, snd.seq = 17000, snd.ack = 11000
   and the offered window is 32000.

    a. If the segment that has sequence 11000 was actually lost, how
       many more segments can the sender send before having to stop.
       (Assume NO timeout occurs).


    b. Suppose that the sender has stopped when the 3rd duplicate ack
       arrives. What the receipt of the third duplicate ack cause
       ssthresh and cwnd be set to.

       ssthresh -


       cwnd -


    c. How many additional duplicate acks will have to be received
       before a NEW segment can be sent.




    d. Assuming that ONLY the 11000 segment was lost what will be the
       leading edge of the usable window when the first ack for new
       data is received.