CS 640 - Midterm Exam
October 19, 1994


(20) 1. In BSD UNIX, abstract endpoints of communication, called sockets, 
are used to provide interprocess-communication (IPC). 
Describe the parameters which define each instance of a socket, and provide 
examples of possible parameter values. 
Also, discuss why it is important to name sockets, and provide an example 
of one way in which sockets may be named (i.e., what does the name look like).

(15) 2. Let M  = 1101011110100 and G(x) = x**5 + x**3 + x**2 + 1
a. Give the shift register corresponding to G(x).
b. Compute T, the bit string to transmit for the data M and generator polynomial G(x).
c. Let R = 110100100000001111 be the bit string that is received after the above 
transmission occurs. Is this transmission accepted? Why?

(20) 3. a. Explain the difference between circuit switching and virtual circuits. 
b. Define "connection-oriented service interface."
c. What is the relationship, if any, between virtual circuits and connection-oriented 
service interfaces.

(25) 4. The following are used by TCP. Explain each, its purpose, and  how it is 
realized (implemented) in TCP and TCP extensions.
a. 3-way handshake
b. graceful close
c. cumulative acks
d. credits
e. window scaling
f. timestamp for estimating round trip time

(20) 5. Describe link protocol error detection/handling mechanisms. Why are these 
simpler than those of transport protocols. As an example explain why a 3-way 
handshake is not generally used by link protocols.