|
(a) Identify one Packet Switching technique.
[1]
DATAGRAM APPROACH / VIRTUAL CIRCUIT APPROACH [1]
(b) List and briefly explain the three components of a packet. [3]
In each case an explanation should be given
for a mark to be awarded.
HEADER: source/destination address, packet size [1]
BODY: the actual data [1]
TRAILER: sequence number, parity bit, error checking bits [1]
(Do not penalise for including some of the trailer information in
the header).
(c) A typical packet size in today’s context is 512k. Discuss
briefly one consideration when choosing an appropriate packet size.
[2]
AVAILABLE BANDWIDTH [1]
OVERAL SIZE OF THE MESSAGE [1]
ROUTING MECHANISMS [1]
(Award the mark only if explanation is given; give credit for any
acceptable answer)
(d) As technology becomes more complex, and communication more affordable,
applications tend to evolve from one kind of data-flow (simplex, half-duplex,
duplex) to another. Describe briefly in your words one 'real-world'
example of an application evolving in this way. [4]
E.G. TELEVISION [1]
| AS
SIMPLEX: |
A central
transmission to receiving TV
sets. [1] |
| AS
HALF-DUPLEX: |
The
introduction of teletex made it
possible for the receiver to request
teletex pages. [1] |
| AS
FULL-DUPLEX: |
Full
interactive (web-based/on-line
interaction) television. [1] |
(Award marks
for these or any other acceptable answers; many
examples are possible)
(e) The Internet uses packet switching, whereas bank ATMs may use
a duplex
connection on a fixed line. Explain why each is appropriate for its
purpose. [5]
ATMs need only point-to-point [1] communications
with a fixed central host [1], and want good security whilst doing
so [1]. Internet users may want to communicate with hundreds of different
hosts [1]; multiple fixed lines would be infeasible [1], and thanks
to the volume and mixed content, security is less of a
concern [1].
Award marks for these or other valid points.
|