The main disadvantages of wireless networks are:
• Low data rate: maximum of 11Mbps compares to 100 Mbps to computers on cable network. This is particularly affected by numbers of concurrent users and the type of application. It is far less suitable for multi-media applications. In reality, the throughput may be nearer 6 Mbps due to protocol and security overheads.
• Interference: wireless networks can be prone to interference from other electronic equipment and other radio networks, especially if poorly installed.
• More difficulty to upgrade: the newer 54Mbps wireless system due out soon will not be compatible with the existing 11Mbps system.
• Battery life: fat client laptops have a typical battery life of two hours. Thin client devices (palmtops, sub notebooks or electronic tablets) can have battery lives of between five and eight hours.

Example applications
1700-place secondary school
The school is on a sprawling campus. It has a cabled network but the addition of a local wireless network allows it to bring computers to classrooms (where teaching resources are available) rather than going to a dedicated IT room. The school is piloting the network in the modern foreign languages department with 16 laptops in a serviced trolley, and a printer on top. This is stored in the local office to be used in any classroom in the department. If the pilot proves successful the plan is to have a similar trolley in every department. The school are finding the system very useful as a supplement to fixed, cabled PCs which can handle faster data transfers.

210-place primary school
This is a primary with typical accommodation: a Victorian main building, a timber framed annex, two mobile classrooms. A wireless radio network has been installed with three transmitters (able to reach the mobile classrooms with a booster aerial at low cost). 16 laptops are kept in a purpose-built cupboard in the school office (wired up for re-charging) and taken to classrooms as needed. Infants work on laptops in groups of five or six, each sharing three laptops, juniors share them between whole class. The school finds the arrangement adequate and doesnÕt feel the need for a dedicated IT room.

Installation
Radio access points have a range of about 30m in a school building but this can vary up to 200m in open space so it is essential to do a site survey. Metal in the building structure, including reinforcing in concrete walls and floors and metal barriers such as permanent metal formwork or foil-faced plasterboard can cause problems. Radio can, however, penetrate a metal stud plasterboard partition that is not foil faced.

Reception can be improved by (inexpensive) antennae. Cabling will still be needed to link access points/base stations and main servers which will all need power. As portable computers rely on batteries it is important to provide the facility to recharge the machines. Purpose-designed cupboards or trolleys (which will need their own storage space) are available.
Wireless connections can also be made over long distances such as between schools using directional antennae, microwave and laser links. It is especially important to have a wireless network configured by specialists as this can affect system security (for example from hackers) and performance.
BECTA Technology Briefing Paper Wireless Local Area Networks (WLANs)Õ - available at www.naace.org - provides useful guidance and contains a number of references including on standards and health and safety.

Cabling
Cabling is likely to be needed to some extent in all installations, particularly for a large number of users and where a number of multi-media applications are used. The current standard of cabling for connection to devices is untwisted pair cable (UTP) category 5E. Backbone cables between servers and main switches are more likely to be in optic fibre (UTP has a maximum length of 90m). In this way a high data rate can be provided on the backbone, currently around 1GBps but likely to increase to 10GBps in future. There are guidelines on installation of network cables such as ANSI/TIA/EIA-568B, CENELEC 11801 and CENELEC-EN 50173/4. As cable types may need to be upgraded in the future, sufficient space in main trunking routes should be allowed to accommodate future needs.
Guarantees on system installation are essential. The main testing standards for copper is the permanent link test (TIA-TSB-95 and ISO/IEC-11801-2000). Appropriate testing devices (such as Fluke or Wirescope) should be used.

Infrastructure
As technology is constantly changing, building infrastructure should be designed for change. It is important to consider, for example, trunking routes and the positioning and servicing of servers. The relevant standard for this is ÔPathways and SpacesÕ (ANSI/TIA/EIA-569-A).
If file servers are sited in unoccupied rooms the need for air conditioning may be reduced as the computers themselves can withstand higher temperatures than people. However there have been reports of unreliability where several servers are located in a small space without ventilation. Access will be required for management on a regular basis and a secure ICT office is a preferred solution..