Computer Science 825
                         Quiz 4              Name _______________________

1. If K stations share a CSMA bus and the probability that any station
   will transmit on a given contention slot is "p", then the probability
   that a successful transmission will take place in a slot is:

   a. p                            b. k * p * (1 - p) ^ (k - 1)

   c.  k * p * (1 - k) ^ (p - 1)   d. None of the above.

2. If the probability computed above is denoted A, then the probability
   that a contention interval will last exactly j slots is:

   a. A ^ (j - 1)  * (1 - A) ^ j    b. A / j

   c. j * (1 - A) ^ (j - 1)         d. None of the above.

3. Suppose that the average length of a contention interval on
   a CSMA bus is C and that the average time to transmit a packet is P.
   The efficiency of the channel is:

   a.  P / C                        b.  (P + C) / P

   c.  C / (P + C)                  d. None of the above

4. Each time an IEEE 802.3 Ethernet station suffers a collision
   (without having a successful transmission) the mean delay until
   its next attempt

   a. Increase by tau (the one       b. Increases by 2 * tau
      way prop delay).

   c. Doubles                        d. Increases by a factor of 2 ^ n
                                        where n is the number of
                                        collisions

5. Answer the following T or F. (Assume only the parameter indicated
   is being varied and all of the others remain fixed in each case).

   ___ a. Increasing the average packet size will tend to make the efficiency
          of a CSMA CD LAN higher.

   ___ b. Increasing the physical length of a CSMA CD LAN will increase the length
          of the contention interval.

   ___ c. Decreasing the bit transmission rate from 10 Mbps to 1 Mbps
          increase the efficiency of a CSMA LAN

6. The principal advantage of the use of switched hubs when compared to
   shared media hubs in an Ethernet environment is that:

   a. Latency of delivery time        b. The effective throughput of the
      is reduced                         net in bps can now exceed link speed.

   c. It makes it possible for two
      source stations to transmit
      simultaneously to a common
      destination.

7. The principal advantage of "cut-through" switching over "store-and-forward"
   switching in a switched Ethernet environment is that:

   a. Latency of delivery time        b. The effective throughput of the
      is reduced                         net in bps can now exceed link speed.

   c. It is possible to conduct       d. It makes it possible for two
      parallel transmissions through     source stations to transmit
      the hub without collisions         simultaneously to a common
                                         destination.

8. For the IEEE token bus match the control packets with the conditions
   underwhich they are used. (Some answers may or may not be used
   multiple times and some may or may not be used at all.)

   ____ a. A station is powered up, transmits   1. SOLICIT_SUCCESSOR_2
           CLAIM_TOKEN detects a collision
           but hears nothing after the          2. WHO_LEADS
           collision ends

   ____ b. A station wishes to leave the net.   3. WHO_FOLLOWS

   ____ c. A station transmits the token twice  4. RESOLVE_CONTENTION
           without hearing its successor
           transmit a token or a packet.        5. CLAIM_TOKEN

   ____ d. A station wishes to invite a new     6. SOLICIT_SUCCESSOR
           station to enter the network.
                                                7. SET_SUCCESSOR