You may have already come across computer networks in your business or home. In its simplest sense a computer network is two or more computers connected together using a telecommunication system for the purpose of communicating and sharing resources. This telecommunications system can be wired, wireless or a combination of both; it can spread over a short distance, such as within a single building, or over much larger distances, such as the global network which comprises the internet. This guide is meant as a high level introduction to computer networks for the manager who doesn't want to get involved in the technical details but wants to know enough to discuss networking with their IT guys.

Types of networks

For the purpose of this article we will only discuss two of the types of networks because those are the two which are most important for the manager of an SME. When most people think about a network they picture a room or building with each of the computers connected together using either cables or a wireless system. This type of network is called a local area network or LAN and is generally restricted to computers and resources within a small geographic area. This is generally the first type of network a company will choose to implement as it enables computers to share resources such as printers and faxes and also enables digital transfer of files and data between computers.

Local Area Network (LAN) example

If a company has two sites at different geographic locations and they want to expand their network to encompass the two then a new type of network is required. Each of the sites is networked using a LAN and then the two sites are joined together using a different technology to form a wide area network or WAN. A WAN is basically two or more LAN's connected using some form of long distance telecommunication system. This can be as simple as a standard analogue telephone line or as complex as a satellite relay system. The physical medium itself is not important, what is important is the logical connection between the two local networks.

Wide Area Network (WAN) example

Wired or Wireless?

There is no right or wrong answer to this question, it it is very much dependant on the specifics of the network; how it will be used, the space into which it will be installed and other factors such as cost. With recent advances in wireless technology the old problems of security and poor performance are no longer really a massive issue. Wireless networks are intrinsically easier to gain access to if the access point is not correctly secured but a good IT technician will be able to implement security which will thwart all but the most determined hackers. Similarly wireless networks can be negatively effected by other electrical devices within the local vicinity but good design and quality hardware can ensure that this does not become a big issue.

Security and performance aside there are other factors which should be taken into account when making the choice. The first and perhaps most important is the ease and cost of installation. Wireless technology is more expensive than it's wired counterpart but doesn't require the laying of cables between computers and networking equipment. In new builds this is often not an issue but where companies are located in older buildings this can be a significant incentive to use wireless. The extra cost of a wireless access point pails into insignificance when compared to the massive cost of retro-fitting cables into an old building. Wireless is also very flexible and enables people using mobile computers such as laptops or PDA's to access the network from any location within wireless range. This is obviously easier than having to locate a free network point every time network access is required.

With the benefits of wireless one might wonder why wired networks are used at all. The simple answer is speed and scalability. The one area where wired networks excel when compared to wireless is the speed that data can be sent between different nodes on a network. The current maximum bandwidth for a wireless network is 54Mbps but wired networks can easily achieve 1Gbps and 10Gbps is just round the corner. When used for large corporate LAN's, wireless is simply not fast enough for the vast amounts of data that are transmitted.

Networking Glossary

Hubs & Switches

In order to form a network each computer or resource (node) must be connected to every other computer or resource. When networks were first conceived each node was directly connected to every other node such as is shown in the first diagram. This was the method used to connect telephones together when they were first developed and works fine if there are only a few nodes to connect. As networks grew this became impractical so other methods of connecting nodes were designed such as daisy chains or ring topologies. Whilst each of these has benefits the modern business network almost always uses a star topology, as depicted in the second diagram, using either a hub or switch to connect the devices. This is obviously far more efficient and uses the least number of connections but does result in there being a single point of failure for the network.

Hubs and switches are physically very similar but work in a very different way. A hub can be thought of as a dumb connection, physically joining each of the computers together but playing no intelligent role in the networks operation. A switch also connects the computers together but unlike a hub it filters the data to improve network efficiency and speeds. Switches are almost always used instead of hubs in modern networks because of the added benefits.

Routers

A router is a more complicated device that connects two separate networks together. In our example WAN above a router is used at the boundary of each LAN to provide a junction between the two LAN's and the telecommunications network. The router acts as an interpreter, taking data from each LAN and routing it through the telecommunications system to the other.

If you've come across a router before it might well have been to connect a LAN to a broadband Internet connection. In this example a router is connecting a local area network to the much larger network this is the Internet. In these cases the router will often be a multi-function device containing a router, switch, firewall and wireless access point in one compact package.

Modems

A modem is a device which takes a digital signal (Composed of 1's and 0's) and encodes and decodes it into an analogue signal. The purpose of this is to enable the transmission of the digital data used by a computer over analogue transmission systems such as telephone or radio. The most obvious form of this technology, which most people will be aware of, is a computer modem used to connect to the internet over a telephone line.

Routers will often have built in modems to connect to specific WAN telecommunications systems such as ADSL, Cable or ISDN. Each of these is a different technology which requires a specific modem but much of this is hidden from the end user who simply buys the correct router and connects it to the telephone or broadband point.

Firewalls

A firewall is a piece of security hardware or software which sits between two networks and filters information flowing between them. At its most basic level a firewall will block certain communications completely but more sophisticated firewalls will actually scan incoming and outgoing communications to determine if they are allowed or if they pose a threat to security. All businesses connected to the internet should at the very minimum use a firewall to protect their network from outside threats. Without one their network is effectively open for anyone to access from anywhere in the world.