Exercise 11 (4.-7.4.) (Tanenbaum pp. 502-573)

1. Answer shortly the following questions ("review type" problem: answers are usually found in
lecture notes or in Tanenbaum's book).
a) What happens when two users try to connect to each other at the same time? What happens if both sides disconnect at the same time?
b) Is it reasonable to use in transport layer the same kind of buffering as in the data link layer? If not, what kind of buffering should be used?
c) How does transport layer recover from disconnection caused by the crash of the machine supporting one communicating transport entity?
d) What is the silly window syndrome? How it can be prevented?
e) Where is the Nagles Algorithm needed and how does the algorithm work?
f) What does indirect TCP mean and what problem it tries to solve?
g) Why does UDP exist? Would it not be enough to just let user processes send raw IP packets?

2. Discuss the advantages and disadvantages of credit versus sliding window protocols. (Credit protocol = the receiver informs the sender how many messages the sender is allowed to send.)

3. a) How does the TCP-protocol handle congestion control? Explain what do concepts slow start and congestion window mean and how they are used in the congestion control of the TCP protocol.
b) A TCP machine is sending windows of 65 535 bytes over a 1-Gbps channel that has a 10-msec one-way delay. What is the maximum throughput achievable? What is the line efficiency?

4. a) Consider the effect of using slow start on a line with 10-msec round-trip time and no congestion. The receive window is 24 KB and the maximum segment size is 2 KB. How long does it take before the first full window can be sent?
b) In a network that has a maximum TPDU size of 128 bytes, a maximum TPDU lifetime of 30 sec, and an 8 bit sequence number, what is the maximum data rate per connection?

5. Explain what happens when a message is transmitted from an application process A to another application process B. The application processes are situated in hosts of different LANs in the same Internet area. Go through all the layers of the TCP/IP protocol from the application program to the LAN.
Explain how and what the application gives to the transport layer, how the transport layer gives the message to the network layer, how the nerwork layer transfers the message to the LAN of the receiver and how the message is finally delivered to the applicati B.
Essential concerns : who does what, from where it gets all the necessary information (OSPF protocol can be skipped), what information unit is dealt with in each layer.

6. a) What part of the material included in the course was most unnecessary, what subjects should have been thoroughly?
b) The Data Communication course is now under reconstruction. Next spring part of the material will be included in a 2 cu course that is compulsatory for all cum laude students in Computer Science, rest will be included in a optional specialist course. What subjects, in your opinion, should be included in the compulsatory course and what should be left to the specialist course?
c) Fill in (now or later) the class feedback form for Data Communication course.

This is the last problem set for this Data Communication course. The 2. exam is on Monday 10.4. in Room 1 in The University Main Building.