Exercise 7 (22.-26.3) (Tanenbaum pp. 273-313)
1. Answer shortly the following questions ("review type" problem: answers
are usually found in lecture notes or in Tanenbaum's
book).
a) The protocols of 802 series can by categorized also by
their suitability to office environment or factory environment. Which protocols
suit which environment? Why or why not?
b) How are sending turns agreed on in a DQDB-network?
c) How is the work divided between LLC and MAC layers?
d) What is the essential difference between a repeater and a
bridge?
e) A transparent bridge has ports to many LANs. How does
the bridge learn to know from which direction different hosts
are to be found?
f) Suppose a work station has not sent any messages at
all. How can it get a message from another work
station situated in a LAN behind many bridges?
2.Stations A, B, C and D use CMDA to transmit data.
Station are assigned following chip sequences:
A: 00011011, B: 00101110, C: 01011100 and D:01000010.
a) What is the resulting signal if stations A, B and C
send simultaneously 0-bit?
b) When the receiver gets the signal (-1 +1
-3 +1 -1 -3 +1 +1), what stations have been sending and which bit
each has sent?
3. Encode the bit sequence 0001110101 using
a) Manchester encoding
b) Differential Manchester encoding (assuming that in the beginning
the line is low position).
c) How does the receiver know where a bit begins when differential
Manchester encoding is used?
4. a) A small 1 Mbps Ethernet-bus is 1800 m long. What is the minimum
size of a frame?
b) Three stations start sending 'simultaneously'. The size of
the message sent by each station is 1200 bytes.
How long does it take for all the messages to arrive? (Network 802.3 LAN,
10 Mbps)
5 a) Different priority classes of a token bus LAN have following timer
values: T6= 40 ms, T4= 80 ms,
T2= 90 ms, T0= 100ms. What fraction of the total bandwidth
is reserved for each priority class?
b) What kind of guarantee does a token ring give to the
throughput time of a message? Is the guarantee always valid?
c) Give an example that clarifies the usage of the reservation
bits in the token ring.
6. The token can get lost, because the station holding the
token is disconnected from the network.
a) How does the token bus handle the situation? b) How does
a token ring handle the situation?
At least three problems should be solved including problem 1.