exercises

在linux下模拟不同数据链路层协议的工作状况

The simulator provides a playground for experimenting with data link
protocols.  Here are some suggestions for possible student projects using
the simulator.  Most of these will require drawing many graphs, so it
would be helpful if some tools for turning numbers into graphs are available
locally.  The UNIX grap frontend for troff is one such tool, but others exist.

 1. For one or more selected protocols, make a study of protocol performance,
    measured in payloads delivered per second, as a function of the checksum
    error rate, lost packet rate, and timeout interval.  For example, provide
    graphs showing payloads/sec as a function of timeout interval, for
    various error rates.  What can you conclude?

 2. Compare the performance of protocols 5 and 6 in detail with respect to
    payloads/sec and number of retransmissions for a wide variety of
    parameters.  Under which circumstances is protocol 5 better? protocol 6?

 3. The function pick_event() has built-in priorities for events. For example,
    for protocol 5, frame arrivals go before timeouts.  Experiment with
    changing these priorities (by reordering the statements in pick_event().
    What conclusions can you draw?

 4. Investigate the number of retransmitted frames as a function of the
    timeout interval for various parameters?  Can you determine what the
    optimum setting should be?

 5. Presently, the simulator advances time one tick at a time.  If both
    processes are blocked on distant timeouts, this process goes slowly.
    Change the simulator to advance time more quickly when both processes
    are blocked on the clock.

 6. In the simulator at present, packet delivery is essentially instanteous.
    Change it so that delivery times are variable with a user-settable
    variance.  How does the variance affect protocol performance?