Computer Science 481/681
                         Quiz D           Name _______________________


 1. a. Identify one advantage of the use of the TCP "Keepalive"
       timer.




    b. Two disadvantages of its use include: it generates some extra
       packets and if you pay for packets it costs you $$$'s. Identify
       one other disadvantage.




    c. People that don't like the TCP keepalive timer claim that
       such a function should rightly be provided:

       1. At the network layer         2. At the datalink layer

       3. At the transport layer       4. At the session or app layer.

 2. The function of the TCP persist timer is to:

    a. Ensure that the TCP at the other  b. Ensure that a packet that
       end has not crashed when no data     has timed out is eventually
       have been exchanged for a long       delivered.
       time.

    c. Recover from lost window size     d. Recover from half-closed
       update packets.                      sessions.


 3. Suppose that two TCP's are connected by a transcontinental link
    that has supports a transmission rate of 100 MegaBytes/second
    but has a two way round trip transit time of 50 millisecs.  What
    is the maxium effective throughput (in bytes per second)
    on this channel if the receiver offers a window of 50KBytes.











 4. The performance problem associated with Fast Transmit and Fast
    Recovery in LFN's is:

    a. More than one lost segment      b. More than two lost segments
       per window causes a                per window causes a
       pipeline drain.                    pipeline drain.

    c. It is essentially equivalent    d. It is essentially equivalent
       to a stop and wait                 to a Go-back-N protocol.
       protocol.

 5. Suppose bit transmission rate on a LFN is 10^9 bits/second and
    round trip transmission time is 48 milliseconds.  What is the
    minimum value that can be specified in the TCP Window Scale
    Factor Option if transmission is to avoid being halted by
    window size limitations.









 6. The TCP timestamp option is used to address both  performance
    and reliability issues in LFN's.. Describe how in both cases:

    a. Performance -





    b. Reliability -





 7. As described in class the sequence number wrap problem in the
    LFN domain is more of a problem:

    a. Because sequence numbers     b. Because the high rate at which
       can quickly wrap within         sequence numbers are consumed
       a given connection.             make it likely that a delayed
                                       duplicate from an old connection
                                       will be accepted.
    c. Both situations are equally
       problematic

 8. The sequence number wrapping problem can occur:

    a. Any time a very large window b. Any time a very high transmission
       is used regardless of the       rate is used regardless of the window
       transmission rate.              size

    c. Only when high transmission
       rates and large window sizes
       are used together.

 9. Large window sizes are needed

    a. Anytime Gigabyte transmission b. Any time propagation delays are
       speeds are used.                 > 100 ms.

    b. Only when the product of the
       trasmission rate and the
       propagation delay is large.