Computer Science 825
                         Quiz 5              Name _______________________

1. A token ring monitor will set the "M" bit on whenever it sees:
   (Check all that apply)

   ___ a. A 0 priority data frame.

   ___ b. A high priority token

   ___ c. A 0 priority token.

2. In an 802.5 token ring system suppose the following events occur:

   Station A transmits to E using priority 2 token
   Station C makes a priority  5 reservation
   Station A generates a priority 5 token
   Station B transmits a priority 5 message to station C
   Station B transmits a priority 5 token
   Station C transmits a priority 5 message to station B

   Who is responsible for regenerating a priority 2 token?

3. Two standard measures of network performance are sustained throughput
   and mean packet delay. High sustained throughput is good and low mean
   packet delay is good.  For each of the following select the answer that
   bests compares CSMA/CD with token passing.

   a. Sustainable throughput at very high loads
      1. CSMA/CD is better          2. Token passing is better
      3. No measureable difference

   b. Packet delay at very high loads
      1. CSMA/CD is better          2. Token passing is better
      3. No measureable difference

   c. Packet delay at very low loads
      1. CSMA/CD is better          2. Token passing is better
      3. No measureable difference


4. Suppose the following bit sequence is subject to SDLC style
   bit stuffing.. How many bits will actually be transmitted?

                        2         1
                  65432109876543210987654321
                  --------------------------
    Last bit -->  11100111111101111011111000 <- First bit transmitted



5. Suppose a 15 bit codeword with ODD parity is being used in a
   single bit hamming ECC.  Suppose the  following codeword is
   received.

      X     0     1  0  1  X  1  0  1  0  0  1  1
      --------------------------------------------
      1  2  3  4  5  6  7  8  9 10 11 12 13 14 15

   a. Fill in the  missing ECC bits above ..

   b. Suppose a single bit Hamming ECC is to be performed on a
      1023 bit codeword.  How many bits are in each of the 10
      parity checked groups (include the parity bit itself).



   c. How many bits does any pair of parity checked groups
      have in common with each other?



   c. Suppose a two bit error occurs. Circle the correct description
      of the result.

      1. The fact that there is a two error can be detected, but the
         error can't be corrected.

      2. The two bit error will be undetected and the value that results
         from the correction process will be a legal code word but it
         will be the wrong one.

      3. The two bit error will be undetected and the corrected value will
         be either the wrong codeword or it might be the correct codeword.

      4. The two bit error will be undetected and the corrected value MAY
         be an illegal code word.

    d. What is the minimum Hamming distance of a code that is capable
       of doing double bit error correction?



6. Suppose 1800 bit code words are to be transmitted and it is desired
   to use a Hamming code to correct single error bursts of up to 30 bits.
   How many of the 1800 bits must be used for ECC. (Hint: Fractional
   bit based strategies are not encouraged!)




7. Suppose the MLMA MAC protocol is being used and station addresses
   consist of 3 decimal numbers. If stations 610, 501, 403, 199 and
   and 197 all become ready at the same time. How many decades will
   be required to identify the ready stations.





8. Both MLMA and PURE binary countdown provide favorable treatment
   to high numbered stations.  The degree of favoratism is:

   a. Higher favoritism for PURE    b. Higher favoritism for MLMA
      binary countdown than MLMA       than pure binary countdown

   c. Roughly the same degree for
      both.