Task: Learning Journal

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Good notes will help you organise and process data and information

The bus network topology

In a bus network all the workstations, servers and printers are joined to one cable (the bus). At each end of the cable a terminator is fitted to stop signals reflecting back down the bus.

Operation

The bus topology was the first implementation of an Ethernet network. In this type of network, network signals, representing messages between devices, are sent through the main cable to reach all connected devices. Each message contains a destination address that identifies its intended recipient. The MAC address that is hardcoded into the Network Interface Controller (NIC) of each device, is used for this purpose. The intended receiving device picks up the communication and all other devices ignore it.

Collisions

If two (or more) devices try to transmit at the same time, it will cause a collision, i.e. the signals will interfere with each other. If a collision occurs, the devices must stop and try again later. Each device waits a different random amount of time before trying again. At times when the network is in heavy use, lots of computers will be transmitting data, leading to a high number of collisions. This causes the overall performance of the network to deteriorate.

Security

The fact that signals are transitted across the whole network can be a security issue because every device attached to the bus can "read" every message, unless the messages are encrypted.

Reliability

A failure of the main bus cable will bring the whole network to a stop. However, if there is a break or failure in the cable that connects a single device to the bus, it will affect just this device; the rest of the network will carry on working.

The star network

In a star topology each device on the network has its own cable that connects to a central communication device such as a switch or hub see below.

Operation

If the central device is a hub, network signals that reach the hub are sent out to all connected devices. The hub does not process the signals that pass through it, but just repeats them on all of its connections.

However, a switch uses a table that maps each device to the port it is connected to. In this way, the switch is able to direct messages only to the correct recipient (receiving device).

Security and speed

Use of a switch improves the security and speed of a star network. Messages are transmitted along a specific path from source to destination, so they do not pass through every cable in the network.

Reliability

In a star network, the switch or hub is a central point of failure. If this component fails, none of the connected devices will be able to communicate or access network resources. However, a failure of any of the individual cables or workstations will not affect the network. If one workstation fails, the rest of the network can continue to operate.

Task:

Open your student workbook at page 10 Read through the notes then complete the following task in your book.

1. Task 4

When you are finished screenshot your answer into your Learning Journal