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A switch is a device that connects several devices (e.g. computer, printer) together to enable communication to take place between those devices. It consists of a number of ports into which cables can be connected. Data packets that are received by the switch are examined for their destination and then sent to the port which is connected to the recipient device. In a large organisation, several switches will be used together and connect to a core switch. The core switch (sometimes known as a backbone switch) will manage all the data being received by other switches and then route it to other switches connected to it.

Managed switches can be configured so that data through each port can be controlled in different ways. Bandwidths can be limited to each port or priority can be given to data on a particular port. For example, some ports may be set to run at 1Gbps, whereas others may be set to 100Mbps. Switches can also be configured for QoS whereby priority can be given to particular applications which require a guaranteed bandwidth, such as video conferencing or voice over IP.

Other configurations include being able to set up a virtual LAN and being able to monitor traffic for potential problems.

For example, if two devices are connected to ports 1 and 2 and they need to communicate, then this can happen at the same time at two devices on ports 3 and 4 because the ports operate independently of each other and thus collisions do not occur.

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A hub looks physically the same as a switch and has the same purpose of enabling communication to take place between devices that are connected to it. However, it does not examine the data packets, but instead sends them out to every port that is connected to it. This means that data then has to be filtered by recipient devices to see whether it is intended for that device. It also means that data is more susceptible to interception. Another problem caused by sending data out through all ports is that more collisions can occur. Considering the activity used for a switch, the two devices connected to ports 1 and 2 are communicating at the same time as ports 3 and 4, but because there is no independence between the ports, collisions will occur.

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A wireless access point (WAP) is a hub that communicates wirelessly instead of having physical connections through ports. The WAP is usually connected to the main network infrastructure through a single cable connected to a switch. Any wireless enabled devices such as laptops, PDAs and mobile phones can connect a WAP. Radio signals are sent from the devices and received by the WAP and then sent to the network or another wireless device. When a WAP receives a signal intended to be received by a wireless device, it broadcasts it and the receiving device collects the data packets.

A major problem with WAPs is the potential for hackers to intercept data. Therefore, WAPs provide encryption methods. WAPs are used in homes, small organisations and large organisations where wireless devices need to be connected to the network.

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A network interface card (NIC) enables a computer to be connected to a network using a cable. More modern computers include the network interface as part of the circuitry on the motherboard of the computer, but it is also possible to add network interface cards to computers.

Each NIC has a media access control (MAC) address that is unique to that card. Other devices that are connected to networks also have MAC addresses so they can be identified uniquely.

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In order to communicate with a WAP, a device needs to have a wireless NIC. These can take the form of:

part of the internal circuitry of a laptop computer or printer

a USB wireless dongle that can be connected to any USB port

an adapter card that fits in to a PCMIA slot on a laptop or an expansion slot on a desktop computer.

The wireless NIC must support the same communication standard as the WAP. It will have a MAC address like a NIC.

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A router is an advanced version of a switch. It stores the addresses of devices connected to it and sends data to recipient devices using an effective route. It is mainly used to connect a LAN to a WAN. Routers were once used exclusively by large organisations, but smaller versions of routers are now available to connect home computers to the internet.

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Signals deteriorate along long cables, so a device is required to extend the range of cables. A repeater will sit between two segmenets of cable. It receives the signal from one cable and then re-sends the signal along the next cable. It is used when copper cable needs to be used over distances longer than 100 metres.

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A bridge is used to connect two LANs together. It is different to a router in that it does not store the addresses of devices connected to it.

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A server is a powerful computer that performs functions on behalf of clients connected to it. There are many different types of server and the size and functionality of a network will dictate how many are needed. The most common types are described below.

File Server

A file server stores files available on the network. It will normally have storage areas set aside for each user on the network that are only accessible to those users. It is also likely to have 'shared' files that are available to some or all users. Examples of shared areas in a school could be:

Student - all users on the network can read any files sorted in this area.

ICT - only the ICT staff can make changes to the files.

Geography - only the Geography staff can make changes to the files.

History - only the History staff can make changes to the files.

Staff - staff can read any files, but students can not access the files at all.

Secure - only staff who have been given permission can read or change files stored in this area.

Finance - only financial staff can read or change files.

Admin - only administrative staff can read or change files.

Users can access their files from any client connected to the network.

Application Server

An application server stores software for use across the network. It performs two main functions:

Storing software so that it can be run from the application server by a client computer.

Storing software installation files so that software can be deployed to client computers.

When software is stored so it can be run from the application server, this saves storage space, memory and processing power on client computers, but does increase the amount of network traffic. When software is deployed to client computers, reliance on the network is reduced, but more processing power, storage space and memory are required by the clients.

Mail Server

A mail server manages all emails for an organisation. It will receive all incoming emails and allocate them to the appropriate inbox. It will only allow authorised users to access their own mail boxes. Any emails sent by users will be sent by the mail server either to another user on the LAN or via a router to a WAN or the internet. The mail server will perform additional functions such as:

checking all incoming emails for viruses

filtering out any SPAM emails

providing a central address book for the organisation

settling limits to the size of mailboxes

calendars.

Proxy Server

A proxy server manages access to the internet within an organisation. It can carry out the following functions:

Store web pages that have been visited in a cache so that the next user to visit web pages stored in the cache will haeve faster access to them.

A firewall that examines all data coming in to (and sometimes going out of) the network and blocks access to unacceptable internet traffic.

Filter access to web pages so that undesirable web pages are blocked.

Print Server

A print server manages access to printers within a LAN. Print jobs are sent by client computers to the print server where the print job is processed, reducing the processing burden on the client computers. The print server will put all the print jobs for each printer into a queue and deal with them in turn. It may also provide some of the following functions

Prioritise print jobs so that urgent ones can 'jump' the queue.

Charge users for each print job.

Restrict the number of pages that can be printed at once to a printer.

Restrict access to certain printers so they can only be used by specific users.

Provide reports of who has printed what.

Back-Up Server

The role of a back-up server is to back-up all data on a network so that individual users do not have to back-up their own data. While many users rely on back-up servers as their sole form of back-up, it is good practice for users to back-up their own personal files. A back-up server will usually have tape drives conncected to it and back-up jobs will be scheduled so that they run automatically each day - usually overnight.