1 (i) What is the difference between band width, baud
rateand channel capacity? [5]
(ii) What is the difference between a confirmed service
and unconfirmed service? For each of the following tell
whether it might be a confirmed service and unconfirmed
service, both or neither: [5]
· Connection establishment
· Data transmission
· Connection release
(iii) Why is a virtual terminal protocol needed? What
kinds of applications are likely to use it? [2]
(iv) Sketch the Manchester encoding for the bit stream:
0001110101 [2]
(v) A group of N user stations share a 56 Kbps pure
Aloha Channel. Each station outputs a 1000 bit frame
on an average of once every 100 sec (stations are buffered).
What is the max value of N? [5] (vi) If the bit string
0111101111101111110 is subjected to bit stuffing, what
is the output string? [2]
(vii) X .21 does not provide for multiplexing at layer
3. Why? [4]
(viii) With reference to ISO reference model, point
out which layer/layers carry the following functions:
[5]
· Text/data compression
· Virtual terminal management
· Connection management
· Error free data transmission · Deadlock
control
2 Explain the operations of CSMA/CD Bus and token passing
bus. Compare advantages and disadvantages of each. Why
is the latter favoured for real time application such
as process control? [15]
3 (i) Explain the following ISO Terms: [6]
· Service data unit
· Interface data unit
· Protocol data unit
(ii) Describe a situation in which protocol data unit
is different in size from interface data unit and service
data unit. [6]
(iii) What are the different service primitives in
the OSI model for connection oriented service? [3]
4 (i) Describe main message errors which typically
occur at the data link layers. Explain how such errors
occur and a method of correction. [7]
(ii) Compare the two data link protocols: Go back N
and Selective Repeat in terms of flow control, error
recovery and packet loss. [8]
5 (i) TCP uses a single transport header whereas OSI
has many of them? Discuss the advantages and disadvantages
of each method. [7]
(ii) Discuss the differences between OSI Class 4 and
TCP. [8]
6 (i) With respect to point to point WAN, distinguish
the following: [8]
* Virtual circuit service and datagram service.
* Adaptive routing and nonadaptive routing
(ii) What is deadlock in point to point subnet? How
is deadlock prevented in such subnet? [7]
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