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Circuit switching, packet
switching, and message switching are all used in networks. Each has different
characteristics. |
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| (a) |
What is the purpose of the various
switching techniques? |
[2] |
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Various
switching techniques is used because it is impossible to arrange point to point
communication during transmission. So, data for various node is sharing a common or same
communication path. |
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| (b) |
Message switching and packet
switching are both used to transmit data without the establishment of a dedicated path or
circuit. Explain |
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(i) how each one operates, |
[4] |
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(ii) how they differ from each
other, and |
[4] |
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(iii) the disadvantages of each one. |
[2] |
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(i)
Message switching
- Message is sent from one node to
another independently depending on the network.
- The receiving node must wait for the
whole/complete message before it can send to another node.
- Work in a store and forward
mechanism.
- Node should have larger buffer to
store the whole message.
Packet switching
- Message is divided into smaller
parts and transmit individually.
- Each packer might route different
paths from sender to receiver.
- The receiving end must be able to
reassemble all the packets that have arrived out of order.
- Also work in a store and forward
mechanism.
- Nodes do not need to have such a
large buffer as message switching.
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(ii)
Message Switching
- Messages are sent as a whole.
- Nodes need larger buffer to store
the message.
- low overhead as there's only one
header and trailer bits.
- Not suitable for interactive
traffic.
Packet Switching
- Messages are broken up into smaller
parts to transmit individually.
- Nodes do not need such a large
buffer as it stores only a small part.
- High overhead as each packet needs
full destination and source addresses information and also the sequence of the packets.
- suitable for interactive traffic.
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(iii)
Message Switching
- low security as the hacker could get
the whole message if he manages to hack one node.
- Not suitable for interactive traffic
as it could be slowed in various form of delays.
Packet Switching
- High overhead as each packet had the
full destination and source addresses.
- Extra step to rearrange and
reassemble it at the receiving end.
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| (c) |
Is message switching suitable for
interactive traffic? Explain your answer. |
[2] |
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No.
Because of various forms of delay. For example, propagation delay and queuing delay. |
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| (d) |
An ATM network uses virtual circuits
to route its cells through the network. Explain what a virtual circuit is, and how this
differs from the datagram approach. |
[6] |
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A virtual circuit is
another technique used in packet switching which route on a virtual path. Differences from datagram:
| Issue |
Virtual
Circuit |
Datagram |
| Circuit
set-up |
required |
no need |
| Routing |
route is
fixed and all packets follow this route |
transmit
individually and independently for each packets. |
| Addressing |
contains
only short VC identifier |
contains
full destination and source addresses |
| Effect of
router failure |
the whole
circuit needs to be re-established |
only the
affected packet needs to be resent |
| Call-termination |
required
- high overhead
Every entry of VC number needs to be deleted. |
not
needed - no overhead |
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