Exercise 11 (26. -30.4.)
(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) How does the TCP-protocol handle
congestion control?
g) What does indirect TCP mean and what
problem it tries to solve?
h) Why does UDP exist? Would it
not be enough to just let user processes send raw IP packets?
i) What protocols exist in the AAL Layer?
How well do these protocols carry out their tasks.
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) 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?
4. a) What is the payload size of the maximum length message that
fits in a single AAL 3/4.
b) When a 1024 byte message is sent with AAL
3/4, what is the efficiency obtained? In other
words, what
fraction of the bits transmitted are useful data bits? Repeat the problem
for AAL 5.
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. Essential concerns : who
does what, from where it gets all necessary information
(OSPF protocol can be skipped), what information
unit is dealt with in each layer.
6. a) The lecturer thinks that the course could
be further improved. What is your opinion of the
following issues:
- what part
of the material was most unnecessary
- what subjects
should have been treated more from the point of view of
- an application programmer (assumed background Rinnakkaisohjelmistot
(Concurrent Systems) course)
- a user of data communication (mobile, ATM, wireless...) ?
b) Fill in (now or later)
the class feedback form for Data Communication course.
This is the last problem set for the Data Communication course. The 2. exam is on Friday 7.5.1999, Porthania I.