Computer Science 825
                           Quiz 5          Name _______________________

1. A buffer in the protocol discussed in class cycled though a number
   of queues.. Associate each transition with the process that
   caused it. (Some answers may be used more than once or not at all).

      ____ 1. Sender window to free        a.  Network layer process
              list.

      ____ 2. Network input to link        b.  Queuemsg process
              station output
                                           c.  Timeout process
      ____ 3. Link output to
              sender window.               d.  Writelink process

                                           e.  Readlink process


2. Suppose that a 3 bit sequence number were being used in the
   protocol discussed in class.  In that case the LARGEST value
   that the semaphore "numslots" could be safely initialized to is:

   a. 2                             b. 3

   c. 7                             d. 8

3. The value of the counting semaphore "wpcount" (that counted the
   number of packets waiting to be written is given by: (assume
   no sequence # wrap).

   a. nxtqueue - nxtack                 b. nxtqueue - nxtsend

   c. nxtsend - nxtack                  d. none of the above


4. As written, the protocol presented in class becomes deadlocked
   when:

   a. any readlink process is blocked   b. all readlink processes are
      in dequeue due to lack of free       blocked in dequeue due to
      buffers.                             lack of free buffers

   c. the network layer input process   d. Either (a.) or (c.) occurs
      blocks in dequeue because its
      input queue is empty

5. When a process becomes blocked on a counting semaphore it
   necessarily depends upon some OTHER process to signal the
   semaphore and unblock it.  For each of the following identify
   the process that is responsible for unblocking it AFTER IT
   BLOCKS ON A COUNTING SEMAPHORE.

   ___ a. network layer           1. queuemsg

   ___ b. readlink                2. readlink

   ___ c. writelink               3. writelink

                                  4. network layer

6. Supervisory frames in SDLC carry

   a. Both sequence numbers and    b. Sequence numbers but no ack
      ack numbers.                    numbers

   c. Ack numbers but no sequence  d. No numbers at all.
      numbers.

7. Which of the following is NOT a use of supervisory frames in SDLC

   a. Sending a standalone ack     b. Seeing if another station is
                                      back up after a crash.

   b. Polling                      d. Telling another station to
                                      temporarily stop sending.

8. The address byte in an S/HDLC packet always carries the address of

   a. The sender                 b. The receiver

   c. The primary station.       d. The secondary station.

9. The "failure" that the SDLC unnumbered protocol is susceptible to
   is:

   a. Undetected loss              b. Undetected duplication of
      of a frame.                     a frame.

   c. Reordering of frames         d. Both a. and b.

10. Suppose a new connection is established between the Host at
    router "A" to the host at router "D" and that it follows
    the route H->A->E->C->D->H.  Update the circuit assignment
    tables in the diagram.