Computer Science 825
                         Quiz 6              Name _______________________

1. a. Write down the resultant bit pattern after the following is subjected
   to SDLC type bit stuffing (flag = 01111110). (Assume the bits are
   processed by the bit stuffer in left to right order.)

      0111011110111110111111011111110



   b. Write down the resultant bit pattern after your answer to (a.) is
   subjected to bit "UN"stuffing by a recipient.



2. Which type of framing was used in each of the following protcols:

   a. Token ring MAC


   b. SDLC


3. a. How many ECC bits are needed to single bit ECC on a 20000 bit code
      word. (If you give me a fractional # of bits, I'll give you a -1!!).



   b. What is the minimum hamming distance of a code that supports single
      bit ECC?



   c. Suppose a codeword is 10000 bits long and single bit ECC that will
      tolerate error bursts of 50 or less bits is desired. How many ECC
      bits will be needed.



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

       1  1  0  0  1  0  1  0  1  1  1  0  1  1  0
      a1 a2 ...........                         a15

   a. Which bit if any is in error?



   b. Suppose a multiple bit error occurs. Which of the following is true.

      1. The fact that there is a multibit error can be detected, but the
         error cant be corrected.

      2. The multibit error will be undetected and the corrected value will
         be the wrong codeword.

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

      4. The multibit error will be undetected and the corrected value will
         be an illegal code word.