August 1997
AN215: ADVANCED NETWORKING

QUESTION 1 (Compulsory)

Total Marks: 20 Marks

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1. (a) Describe three advantages of using a ring topology for a LAN. [3]
point-to-point wiring, permitting mixed-media implementations [1]
simplicity in connection and maintenance [1]
messages generated at each node, allowing long transmission distances and minimising transmission errors [1]
(b) What is noise (in the context of data communications)? Explain two ways in which noise may arise. [5]
noise is any undesired signal in a communications system [1]
[2] each for any two of the following:
thermal noise: random electron motion arises as a result of heat; it is a function of temperature
inter-modulation noise: arises from signals passing through a non-linear medium (and all are) harmonics are generated
crosstalk: occurs when there is electrical coupling between nearby twisted pair or coaxial cables.
impulse noise: may be caused by nearby power-line spikes; irregular, short and relatively high amplitude pulses.
(c) What are two reasons for using layered protocols? [4]
up to [2] each for any two of these, or similar:
help provide for interconnection of systems from different vendors
allow changes to be made at one level (e.g. physical) without affecting end users
reduce design complexity
(d) List two ways in which the OSI reference model and the TCP/IP reference model are the same, and two ways in which they differ. [8]
[In each part of this question at least half of the marks are offered for giving reasons for your answers.]
up to [2] for each of any two of these similarities:
Layered protocol
Widespread standard
Able to interconnect diverse systems
up to [2] for each of any two of these differences:
TCP/IP has fewer layers
TCP/IP has undergone evolutionary development
TCP/IP is not an ISO standard