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AS Computing LAN

Topologies

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Categories of LAN Topology

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Bus Topology

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Bus Topology Operation

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Bus Topology Operation

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Advantages & Disadvantages

Advantages Disadvantages

•Easy to connect a computer or peripheral to a linear bus.

•Requires less cable length than a star topology.

•Entire network shuts down if there is a break in the main cable.

•Terminators are required at both ends of the backbone cable.

•Difficult to identify the problem if the entire network shuts down.

•Not meant to be used as a stand-alone solution in a large building.

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Ring Topology

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Ring Network advantages

The ring topology is specifically designed for use with a LAN and is not suitable for WAN.

Its advantages:

There is no dependence on a central host computer as data transmission around the network is supported by all the devices in the ring.

Very high transmission rates are possible; 10 megabits/sec is typical;

Routing between devices is relatively simple because message normally travel in one direction only around the ring;

The transmission facility is shared equally amongst the users.

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Ring Network disadvantages

The system depends on the reliability of the whole ring and the repeaters, although it can be designed to bypass any failed node.

It may be difficult to extend the length of the ring because the physical installation of any new cable must ensure that the ring topology is preserved.

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Cambridge Ring

It developed at Cambridge University

It has no host computer and none of the nodes need have overall control of access to the network.

Messages in a ring network flow in one direction, from node to node.

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Token Ring Network

At a start, a free token is circulating on the network, to use the network, a machine first has to capture the free Token and replace the

data with its own message.

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Star Topology

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Star Network advantages

It is suitable for WANs where organisations rely on a central computer for the bulk of processing tasks, perhaps limiting the nodes to their local processing needs and the validation of data, prior to transmission to the central computer.

Centralised control of message switching allows a high degree of security control;

Each spoke in the star is independent of the rest and a fault in a link or device in one spoke, can be identified by the computer at the hub;

The data transmission speeds used cab vary from one spoke to another.

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Star Network disadvantages

The network is vulnerable to hub failures which affect all users. As a distributed processing system, some processing is still possible at the nodes but inter-node communication is lost when the host computer fails.

For a WAN, the control of communications in the network required expensive technology at the hub, probably a mini or mainframe computer. Complex operating and communications software is needed to control the network.

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Using a Hub in a Star Topology

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Using a Switch in a Star Topology

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Hybrid Networks

Hybrid networks include:

star-bus network

star-ring network

mesh networks

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Star / Bus Network

Advantages:

•Point-to-point wiring for individual segments.

•Supported by several hardware and software vendors.

Disadvantages:

•Overall length of each segment is limited by the type of cabling used.

•If the backbone line breaks, the entire segment goes down.

•More difficult to configure and wire

than other topologies.

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Star / Ring network

If a single computer fails, it will not affect the rest of the network.

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Mesh Network

Each computer is connected to every other computer by a separate cable.

If one computer blows up, it won’t affect the rest of the network.

The big advantage of this topology is its backup capabilities by providing multiple paths through the network.