|
In the context of data communications
switching is needed because it is impossible to form point to point
connections with all other nodes. Switching provides a way to share
common communication resources.
(a) There are two distinct packet switching
techniques. What are they known as
and what are the differences between them? [5]
(a) datagram and virtual circuit [1]
1
point for issue subject to a maximum of 4 points
Any other relevant points should earn credit
(b) Is message switching suitable of
interactive traffic? Give reasons for your
answer. [2]
(b) No[1] . It is subjected to several types
of delays such as propagation
delay and queueing delay, but in interactive work, delays are to be
avoided. [1]
(c) Is it true to say that ATM networks
are connection-oriented networks? Explain
how the cells (ATM equivalents to packets) are routed. [4]
(c) ATM cells are routed by using virtual-circuits[1].
Firstly a logical circuit is set-up from the source to the destination
nodes.[1] This involves making
entries at each intermediate router. All cells would then follow this
path[1]. Hence, all cells would arrive in order[1]
Other relevant explanation is also acceptable subject to a maximum
of 4
marks
(d) Would it be accurate to say that
since there is no addressing overheads in circuit switching therefore
this technique provides better line utilization than packet switching?
Justify your answer. [4]
(d) NO[1] in circuit switching the bandwidth
is dedicated until it is
terminated[1] therefore in periods of "silence" the bandwidth
cannot be
utilized by other parties.
This often results in poor line utilization[1].
Packet- switching, although having rather high addressing, does not
reserve and bandwidth and therefore in periods of "silences"
the
bandwidth may be utilized by other parties[1]
|