Computer Science 481/681
                         Quiz C           Name _______________________

1. Suppose a TCP packet arrives with ACK=400, WINDOW=1800 and that
   the recipient has state variable SND.NXT=800.

   a. What is the size of the offered window?



   b. What is the size of the usable window?





2. Suppose the round trip transit time is 20 msec and the output
   bit rate is 1,000,000 bits / second.  How large must the offered
   window be in order for the sender not to have to wait on ACKS.





3. If congestion causes the round trip transit time to increase, the
   window size must be:

   a. increased if the sender is       b. decreased if the sender is
      to avoid blocking while waiting     to avoid blocking while waiting
      for ACKs.                           for ACKs.

   c. neither increasing or decreasing
      will prevent blocking (even
      temporarily).


4. Dynamically increasing the window size in response to congestion

   a. Is a good idea and necessary  b. Is a very bad idea and may
      to maintain throughput.          cause a "congestion collapse"

   c. May temporarily increase
      congestion but will not cause
      any type of major "collapse".


5. A sender must stop sending when

   a. snd.nxt >= snd.wnd              b. snd.nxt >= snd.una + snd.wnd

   b. snd.nxt >= snd.una              d. All of the above


6. A byte of data with sequence number "n" has been sent but not acked if:

   a. n <= snd.una                    b. snd.una < n < snd.nxt

   c. snd.nxt < n                     d. snd.wnd < n


7. A TCP receiver will discard bytes of data having sequence numbers

   a. < rcv.nxt                       b. > (rcv.nxt + rcv.wnd)

   c. Both a. and b.                  d. Since TCP is reliable a receiver
                                         is NEVER allowed to discard
                                         anything.

8. When a TCP bulk data flow takes place:

   a. An ack may be sent after any    b. A receiver may wait until
      packet that arrives.               a full window is received
                                         before ACKING.

   c. A receiver may ack every other  d. All of the above.
      packet.

9. The original intent of the Push flag was:

   a. To tell the sending TCP to      b. To tell the sending IP to
      push the data to IP ASAP.          push the data out of the machine
                                         ASAP

   c. To tell the receiving IP to     d. To tell the receiving TCP to
      push the data to TCP ASAP          allow any active read on the
                                         connection to complete ASAP.