CS 640 - Midterm Exam
October 26, 1992

1. (15) Three parts; 5 points for each part; no partial credit.
a. Assume a generator polynomial G(x) = x**5 + x**3 + x**2 + 1 and a 
frame 100101110. Compute the CRC for this G(x) and frame.
b. Give the shift register circuit for the G(x) of part a).
c. Assume data strings of length 10. Give the single bit error correcting 
Hamming Code for the data string 1011000111.

3. (25) Briefly explain each of the following:
a. DLE (Data Link Escape)
b. bit stuffing
c. selective repeat
d. connectionless service interface
e. TSAP (Transport Service Access Point).

4. (20)
a. Briefly explain packet switching, message switching and circuit switching.
b. Give one disadvantage of each.

5. (25) TCP and TP4 are very similar but there are ways in which they differ.
a. Describe two services TCP provides to its users that TP4 does not provide.
b. Describe two services TP4 provides to its users that TCP does not provide.
c. Both TCP and TP4 use a three-way handshake. Explain the problem that a 3-way 	     
handshake is supposed to solve.
d. Why is a 3-way handshake generally not used by link protocols.

6. (15) Describe the protocol features that handle flow control in LAPB (X.25 
Level 2 or BAC 2,8 in the paper "Bit-oriented Data Link Protocols").