1999 CS 487 Final

Closed Book. Show all work.  Two Hours.

1. Define the following terms:

(a) (5 points) protocol

(b) (5 points) packet switching

(c) (5 points) channel capacity

(d) (5 points) delayed duplicate

2. (10 points) Often I send email to a colleague in Venezuela whose
e-mail address is birkbeck@faces.ula.ve.
What, if anything, does my computer (bruce.cs.unm.edu) have to know about his 
to send the mail? 
How can any necessary information be obtained or updated? 
Does it matter whether or not both computers use UNIX?
Explain your answers.

3. (10 points) A computer is connected to another computer through a network
The two computers communicate with
packets, each of which must be acknowledged. If the communication
is error free but the network (due to congestion) will drop a packet with
probability $p$, what is the expected number of times a packet must
transmitted before it is received and successfully acknowledged? 

4. (20 points) My computer is on a IEEE 802.3 (Ethernet) LAN. I login
(via telnet or some similar terminal emulator) to a remote machine 
on a similar LAN. The two LANs are connected by an  ATM.
I start editing a file on the remote machine. Suppose that
I type a line consisting of a single carraige return (one ASCII character). 
Identify each stage in which extra bits are added to my single byte
to facilitate its transfer from one machine to the other.
How many bytes are actually sent between the two machines?
If you do not know the exact number of bits added at each layer,
give an estimate.

5. (20 points) If we look at the link level and the transport level,
it appears that many of the services are duplicated.
(a) Why is error checking done at both levels? Is there any
difference between the error checking methods at the two levels?

(b) Why is flow or congestion control done at both levels? What
is the difference between flow control and congestion control?

6. (20 points) Networks that work at gigabit rates will be used
to connect multiprocessors in cluster computers. Give two
reasons that, although there has been disucussion of a ``gigabit ethernet,''
IEEE 802.3 (Ethernet) is not a good choice for a gigabit network.

What parts of the IEEE 802.3 (Ethernet) standard might be kept in a gigabit
network? Justify your answers.