CS 640 - Final Exam
Spring 1992

Questions 1-16 (True or False - 2 points each)
 
Questions 1-5 refer to 802.5
1. A station can be a stacking station for at most two priority levels.
2. If the maximum bandwidth (in the standard) were increased, the minimum 
frame size would also increase.
3. Any station may become the active monitor.
4. Highest priority frames may be transmitted by a station even if its THT 
has reached zero.
5. Within a given priority level, all stations have equal opportunity to 
transmit frames.

Questions 6-11 refer to 802.3
6. Every station reads every frame transmitted.
7. The backoff procedure on collisions guarantees that no station will be starved.
8. If the maximum network size (in the standard) were increased, the minimum 
frame size would also increase.
9. Ethernet and 802.3 differ by one field in the header.
10. Every station that senses a collision, sends a jam signal.
11. If an ack is not received within a specified time, a retransmission occurs.

12. Virtual circuits are a type of circuit switching.
13. Virtual circuit hop level flow control is handled by the link level protocol.
14. The link layer manages buffer allocation and deallocation for the network layer.
15. IP uses entry-to-exit flow control.
16. The bandwidth delay product is a measure of how much pipelining is needed for 
efficient operation of a window oriented transport protocol.

Questions 17-40 (fill in the phrase that completes the statement - 2 points each)

Two reasons for having sending stations rather than receiving stations remove 
frames from an 802.5 ring are (17) _____  and (18) _____ .

In CQL, buffers are allocated to (19) _____ .

In SBP, buffers are allocated to (20) _____.

CQL prevents (21) _____ deadlock but is susceptible to (22) _____ deadlock.  
(23) _____ hop level flow control prevents both of these types of deadlock.

An advantage of using VCs in a subnet is (24) _____ .

An advantage of using DGs in a subnet is (25) _____ .

Assume a 200 ms round-trip time and a network bandwidth of 500 megabits per 
second. The maximum TCP throughput in this environment is (26) _____ .

If a receiver agrees to use the TCP window scale option with its shift.cnt 
equal to 3, then its maximum receive window is (27) _____ .

Timestamps are used with the TCP echo option to help with (28) _____ and (29) _____ .

After receiving acknowledgements of five successive packets it has sent, a 
sender using "slow start" has a send window of at least (30) _____ .

Van Jacobson proposes that a TCP sender multiply its send window by a fraction 
less than one when (31) _____ 

Traceroute uses the ICMP (32) _____ and (33) _____ features (or types).

An IP Internet Address is (33) _____ bits long and has two fields, a (34) _____ 
field and a (35) _____ field.

Class B and Class C IP Internet Addresses were introduced because (36) _____ . 

If an IP datagram is too large for the network protocol of the next network
if must traverse, then it is (37) _____ .

The IS-IS and RIP protocols are examples of  (38) _____ routing protocols.

A responsibility of the 802.5 active monitor station is to (39) _____.

IP provides a (40) _____ service interface to TCP.

The remaining questions deal with routing:

41. (10 points) Assume the network of Figure 1 with links labelled by costs. 
Assume use of SPF. Show the order in which nodes are added to S where S contains 
nodes for which the shortest path from A has been found.  For each node 
in S, give its predecessor on the path from A, the source node.

42. (10 points) Assume the network of Figure 2 where all links have cost equal 
to one. Consider the routing tables entries at nodes B, C, D, E for destination A. 
Assume use of a distance vector algorithm where routing tables are always exchanged 
at the same time by all nodes. 

After the link B <----> A fails, the entries for destination A are:

	at B	infinity
	at C	B 2
	at D	C 3
	at E	B 2

a) Assume split horizon and hold-down are not used. Give the values for the  routing 
table entries at B, C, D, E for destination A after each of the next two routing 
table exchanges.
b) Repeat a) using split horizon.
c) Repeat a) using hold-down and split horizon.