Unit Three Test, CSCI 361, Computer Networks, 1-April-08

 1)Define a "UART" and describe the six steps of character reception.

 2)Describe character count framing and give its design weakness.

 3)Describe two type of error detection methods and give the tradeoff between
   two types of error correction methods.

 4)Describe the three differences between protocol 2 (stop-and-wait) and
   protocol 3 (PAR) and explain the effect of premature time-outs on the PAR
   protocol.  

 5)Explain how the combination of a long transit time, high bandwidth, and
   short frames create extreme inefficiency.

 6)Explain why sequence numbers must be two times the buffer size in sliding
   window protocols.

 7)Give an overview of PPP (five parts). 

 8)Define "Ethernet," describe the CSMA/CD protocol, and describe "binary
   exponential backoff."

 9)Define bridge, describe the three "routing" steps employed in a "transparent"
   LAN bridge, and explain why or why not this is really routing.

10)Explain why spanning trees are required in  LAN (three parts) and list the
   three steps a transparent bridge employs to construct a spanning tree.

Bonus:  Provide a one line comment for EACH statement in the following
        sliding window (protocol four) example. Do not describe the syntax
        or statement action.  Instead, describe the role of the statement.
        Be sure to note the three outcomes in the while loop: ACK of last
        frame and/or normal delivery, and timeout with retransmission. 
        (Code on reverse side)




















  #define MAX_SEQ 1
  typedef enum {fram_arrival, cksum_err, timeout} event_type
  #include "protocol.h"
  void protocol4(void) {
    seq_nr next_frame_to_send;
    seq_nr frame_expected;
    frame r, s;
    packet buffer;
    event_type event;
    next_frame_to_send = 0;
    frame_expected = 0;
    from_network_layer(&buffer);
    s.info = buffer;
    s.seq = next_frame_to_send;
    s.ack = 1 - frame_expected;
    to_physical_layer(&s);
    start_timer(s.seq);
    while(true) {
      wait_for_event(&event);
      if(event == frame_arrival) {
        from_physical_layer(&r);
        if(r.seq == frame_expected) {
          to_networklayer(&r.info);
          inc(frame_expected);
        } //end of if r.seq
        if(r.ack == next_frame_to_send) {
          from_network_layer(&buffer);
          inc(next_frame_to_send);
        } //end of if r.ack
      } //end of if event
      s.info = buffer;
      s.seq = next_frame_to_send;
      s.ack = 1 - frame_expected;
      to_physical_layer(&s);
      start_timer(s.seq);
    } //end of while true
  } //end of protocol 4