Networks > Getting A Network

Wireless networks

By Lasa Information Systems Team

Wireless technologies can make setting up a computer network relatively simple especially if you have computers all over your building. It can be much easier to move computers around, and laptops especially can become truly portable - no need to plug in that network cable... This article explains the basics of wireless Local Area Networks and highlights other issues to consider before choosing to go wireless.

What is a wireless network?

Wireless network technology allows computers to communicate with each other via radio signals rather than cables. In its broadest meaning, wireless networking includes mobile and satellite phones, pagers, two-way radios, wireless Local Area Networks and modems. This article focuses on wireless networks i.e. computer networks that are generally confined to the same building or site. A wireless LAN is often part of an existing wired network but can also be standalone systems.

Why have a wireless LAN?

The benefits of a wireless LAN may be clear for laptop users however there are a number of reasons why a wireless LAN is useful in general:

• They are relatively easy and quick to set up compared to wired networks
• Many buildings have unsuitable layouts or walls that cannot be wired for various reasons making it impractical to connect a network via cables.
• Cabling can be an expensive task.  Wireless networks do not include this expense.
• It is easy to add new computers to a wireless network.
• It is easy to move a wireless network to a new location.
• If a small number of computers are separated from a main network, a wireless link can be more cost effective than network cabling although it may also be perfectly feasible to use network cabling.
• A temporary wireless LAN can easily be created for exhibitions, or community projects, without the hazard and inconvenience of trailing cables

A wireless LAN is not suitable for every environment however, and there are important issues to take into account before deciding on this option.

Disadvantages of a wireless LAN include:

• The presence of several competing standards. Using different standards on the same wireless LAN will cause problems.
  
• Since communication over the network is via radio waves it is hard to physically limit the extent od the network.  In other words, people may be able to access your network from neighbouring offices, or even a car parked outside.
• Many wireless devices operate in the same 2.4-GHz radio frequency as cordless phones and microwave ovens. These can cause interference to your wireless LAN signal.
  
• Due to the intermittent nature of wireless connections, problems can occur with applications (e.g. Access databases) that require a stable connection.
• A wireless LAN runs at slower speeds than a wired network.  Although manufacturers specify their equipment runs at 55Mbps, the reality is that wireless connections run at much lower speeds.  This become more true as more computers are connected to it.
  
• If you already have a wired LAN installed, the initial costs of adopting a wireless LAN can be higher than extending the wired LAN

Components of a wireless LAN

Typically there are a couple of components essential for a wireless LAN:

Access Points

An access point acts as the main radio transmitter for your wireless LAN.  Access points translate network traffic into radio signals and transmit that signal to wireless enabled computers. An access point can also be connected to an existing wired network via a cable in order to allow wireless enabled computers access to a wired network. You can have more than one access point on a particular network.

Each access point has a limited range within which it can maintain a wireless connection with wireless enabled computers on a network. This range depends on the environment but is typically up to around 90 metres indoors. The range will be shorter if the building structure interferes with radio transmissions (e.g. presence of metal framing, large masonry structures, multiple floors and walls etc.). Performance generally suffers as distance increases beyond the limits of a range of 50-90 metres.

Outdoors, ranges can extend to as much as 250-500 metres, but again this depends upon the environment. The basic range of an access point can be extended using signal boosters which amplify the radio signal.  Specially designed antenna can also expand the range of a wireless LAN.

Where multiple access points are used, each access point's wireless area should overlap with that of its neighbouring access point. This results in a seamless area in which mobile computer users can move around without losing their connection to the network.

Technically most access points can support up to 255 computers.  However in practice, most access points struggle with more than 10.  More expensive hardware can usually support more computers.

Wireless Network Interface Cards (NIC)

These are special network cards installed within wireless enabled computers. The cards pick up signals from the base station and convert them to signals the computer can understand. The cards can be removable USB or PCMCIA cards, or permanently installed inside a computer.

Wireless NICs can also enable computers in which they are installed to communicate with each other directly on a peer-to-peer (or Ad Hoc) basis. Files and printers can be shared this way without the need for an access point. If wireless computers are also part of a wired network via an access point they may not be able to access resources on the wired part of the network. This problem can be overcome by installing special software on one of the wireless computers so it can act as a bridge to the wired network. A wireless LAN could also include some of these components:

Extension Points

Extension points, or wireless relays are similar to the access point.  They extend the range of the wireless network by relaying signals from wireless enabled computers to the access point.

Directional antennae

The antennae built into most access points are not particularly well designed.  The addition of a better antenna can improve the range of a wireless LAN.  There are several different designs of antenna, each of which is suited to different purposes.  Some antenna produce a very focussed directional signal.  Two of these pointed at each other, each connected to an access point, can be used to connect two different locations - this is called a "line of site" connection.  These can bridge quite large (but ublocked) distances.

Wireless LAN standards

There are a number of competing standards for wireless LAN technology. The main technologies relevant for office wireless networks include:

• Various parts of the IEEE 802.11 standard;
  
• Bluetooth

These are considered in more detail below. Other standards (not covered here) exist including HomeRF (designed more for the home network) and Ultra Wide Bandwidth (an emerging technology).

IEEE 802.11 standards

The IEEE (Institute of Electrical and Electronic Engineers) is an organisation that is involved in setting up computing and communications standards. There are several IEEE 802.11 standards:

802.11b

This open standard, developed by the Wireless Local Area Networks Standards Working Group, was until recently the most widely used wireless LAN standard. 802.11b uses the same frequency (2.4 GHz) as appliances such as cordless phones and microwaves and so is susceptible to interference. Speeds of up to 11Mbps can be reached (although 4-6Mbps is more usual). 802.11b is a mature technology suitable for most home and office environments and there are many products available.

802.11a

Products using this standard first started to appear during 2002. High speeds of up to 54 Mbps can be reached (again, less in practice). This standard uses the less congested 5GHz frequency, reducing the potential for interference. Because of the high speed, this standard is more suitable in offices where there are a large number of users and where the wireless LAN is likely to be very busy. Although higher speeds can be reached, more access points are likely to be needed as range is limited to around 50 feet (shorter than 802.11b). The technology is also presently relatively expensive compared to 802.11b. Products using the 802.11a standard are not compatible with products using the 802.11b standard.

802.11g

This standard offers maximum speeds of 54 Mbps.  It uses the same 2.4GHz frequency as 802.11b, and can support 802.11b equipment at the slower speed.  It also suffers from the same interference issues.  802.11g is currently the most common protocol, with the most equipment available.

802.11n

802.11n is currently under development.  The standard offers minimum speeds of 100 Mbps with maximum speeds up to four times that of 802.11g (i.e. up to 216 Mbps). The standard is due to be ratified by IEEE by the end of 2006/early 2007. Manufacturers are already shipping "Pre-n" equipment based on the proposed standard. However as there may be future compatibility problems, it is probably best to wait until the standard has been finalised before buying 802.11n equipment.

Bluetooth

Bluetooth is a relatively inexpensive, very low-powered and short-range radio frequency system designed for small, mobile devices. Bluetooth can be used to link devices such as pagers, PDAs (Personal Digital Assistants - Handheld computers), mobile phones, and laptops. Since Bluetooth also uses the 2.4GHz radio frequency, it is susceptible to interference from microwaves etc. Range is short at up to only 10 -12 metres. This distance constraint makes Bluetooth generally unsuitable for serious LAN implementation, and so not many Bluetooth LAN systems have been developed.

Security issues

All flavours of the 802.11 standard are susceptible to a number of security vulnerabilities.

As wireless networks use radio waves, anyone with the right equipment and know-how could tap into your network from outside your building (or from another office within a shared building). It is possible to encrypt data travelling across a wireless network using a technology called Wired Equivalent Privacy (WEP). However this and other security settings are often disabled by default on wireless equipment. Added to this, WEP itself is not completely secure.Look out for newer products which use a system called WiFi Protected Access (WPA). WPA promises much improved security over WEP. However, it is possible to undermine the added security afforded by WPA if it is not set up correctly. For example it is important to use a good choice of password and security keys to reduce this possibility. It is possible to upgrade some current wireless Network Cards to incorporate WPA - see your manufacturers site for details.

WEP and WPA may provide adequate security for home wireless networks when used in conjunction with other security measures. For office wireless networks, additional measures will need to be taken to ensure security. Virtual Private Network (VPN) technology used in conjunction with wireless networking may provide a solution (see the knowledgebase article Virtual Private Networks for more on this). Basic precautions that should be taken to prevent casual access to a wireless LAN include:

• Enable Wired Equivalent Privacy (WEP) at the highest setting - whilst this does not guarantee security it's worth having.
• Use WPA if available in preference to WEP.
• Set up access points to allow access to known network cards only (each network card can be identified by a number called a MAC address)
• Change the default SSID (Service Set ID or network name) and encryption keys.  The SSID is the name by which an access point indentifies itself.  Using the default SSID suggests to hackers that the rest of your setup is default, making your network a likely candidate for intrusion attempts.
• Turn off broadcasting of the SSID.  This makes it much harder for people to find your network, but you must tell your users what the SSID is so they can connect.
  
• Using a firewall to protect all connected PC's (see the knowledgebase for more on firewalls)
• Install antivirus software on all networked computers, and keep it updated.
  
• Set up network drives and folders with different access rights for different users - password protect files and folders if necessary.
• Put your wireless access point in the middle of the building, to minimise leakage outside.

For more on general computer security issues see the knowledgebase article Safe and sound - keeping your computers and data secure.

Conclusion

A wireless LAN is relatively easy to set up and has many other advantages. However one may present extra security risks that need addressing. The ease with which one can be set up means that these concerns can be overlooked if the network is set up by someone inexperienced without full awareness of the issues. New standards for encrypting data on wireless networks are emerging so hopefully security will be less of a problem in future.

The presence of competing standards means that careful thought needs to go into choosing equipment to ensure that all machines on the network can communicate with each other.  You should also be aware that wireless networks are not suitable for running all software applications. If in doubt, get advice from a competent source.

Provided attention is paid to these issues, a wireless LAN is a good option for many organisations. More information on wireless networking and security issues can be found at the following sites:

• The WiFi Alliance
• TechSoup.org
• Practically Networked's WiFi Security Reference Page