2. Exercise (2. - 6.2.) (Tanenbaum, pp. 16-73)

1. Answer shortly  the following  questions ("review"-type of problem: answers are found directly in lecture notes  or in Tanenbaum?s book):
a) What is  the most important task  of each OSI layer?
b) What are TCP and UDP? How do they differ?
c) How do concepts 'service', 'interface' and 'protocol' relate to each other?
d) What is meant by circuit switching, virtual circuit switching and packet switching?
e) What are protocols X.21, X.25, X.29 used for?
f) Why does ATM use small fixed-length packets?
g) What are ISO, ANSI, ETSI, ITU-T, CCITT?
h) Who are specifying ISO-standards, TCP/IP-standards?

2.OSI layers can be either connected-oriented or connectionless independently of each other. Give examples of environments (application <=> network) where it would be quite possible even reasonable to let adjacent layers to alternate between connection oriented and connectionless (include only those layers where connection-oriented and connectionless has some meaning).

3. In each layer many kinds of disturbance can happen such as

•     the content of a packet is changed
•     a packet disappears
•     the connection breaks for a short time

4. Data communication now and then causes  congestion in the network. How is congestion noticed. What effects  does congestion have? How the network can recover from congestion? Think what kind of  solutions  could be used in different OSI layers. (Don't go into details, principal ideas   for different layers  are  sufficient.)

5.  Why was SMDS designed as a conectionless network and frame relay as a connection-oriented one? How does their  flow control differ? Is congestion anyhow possible?  If so,  what happens then?

6.  Why  is it so difficult  to measure  the  data transfer time from the sender to the receiver acros WAN?

At least  three problems should be solved including problem 1.