Template -- Teachers @ Work

The Technical Requirements & the Managerial Issues of Running a Wireless Network

Firstly, we need to background how wireless systems work. Televisions receive pictures via electromagnetic waves broadcast via satellite or larger aerials placed on local high points. The television receives that signal via an aerial, has it amplified and then converts the amplified signal into the pictures we see. A similar process applies to wireless technology. A standard category 5E cable or similar takes the data to a base station which broadcasts the signal via electromagnetic radiation (radio waves). In order to receive these radio waves each computer needs to have a wireless network adapter housed within it. The computer also needs to be placed close enough to the base station so that the signal is strong enough for the network adapter to receive it, decode it, and present the information on the screen as data from the remote source. This distance depends on the nature of the equipment that is put in place as well as the standards that this equipment uses.

Frequencies

The information can be broadcast from the base station at different frequencies but many countries have set aside certain frequencies that are free and consequently tend to be well used. Other frequencies are sold to radio stations, high-speed Internet suppliers, television stations . . . . Quite often the frequency that is free is in the 2-5 GHz region (generally 2.4GHz). However if a number of different services are broadcasting data at the same frequency these frequencies can interfere with each other, a scenario that could become an issue as more and more everyday items use this frequency. It is even possible that in a school set up with a wireless network that broadcasts at a frequency of 2.4 GHz (802.11b/g standards) will find it’s signal interrupted by garage door openers that also operate at this frequency, local two-way radio users, stereo equipment that broadcasts wirelessly to its speakers, heating systems that receive their data from remote sensors . . . . Of interest here is the fact that Bluetooth wireless technology also uses the 2.4 GHz frequency. Many mobile phones are now fitted with Bluetooth technology and although this technology has a limited coverage area (< 10 m) there is still potential for interference. As the 802.11a standard broadcasts at a 5-6GHz frequency this is less likely to experience interference from other “devices” but it has a lower bandwidth that limits the number of users for each base station.

Another potential problem area could evolve when two or more base stations broadcast information at the same frequency, should the areas to which their frequencies are broadcasting (known as the broadcast footprint) overlap then these two transmitting base stations could interfere with each other It is important therefore to avoid such a situation (see "coverage" below). One-way in which manufacturers have overcome this issue is to assign different zones to each standard. The 802.11a standard (see "standards" below), can cater for twelve zones, while the 802.11b and 802.11g standards have the capacity for only three zones.

Most products produced operate in this free bandwidth zone, however it is possible to purchase equipment which operates in an exclusive bandwidth such as 5.8 MHz (802.11a; see information below) where interference will be far less likely but this comes at an additional cost. It is important that schools do a scan of the region that they are likely to be using over a 48 hour period to see what frequencies are presently being received.

The Institute of Electrical & Electronic Engineers (IEEE) has developed a set of standards to encourage interoperability of different base stations and wireless network adapters. Although the standards are in place, different manufacturers set up their systems quite differently, and sometimes even within the same standard you can find that the wireless network adapters manufactured by one company are unable to receive and/or decode the information sent out by a base station manufactured by a different company. For this reason we encourage schools wishing to pursue wireless networking to use equipment supplied by a single manufacturer wherever possible.

Each of these standards has particular characteristics and is designed for different applications. Each standard has a different capacity for delivering data. A standard modem delivers information at a speed of 56 kilobits per second. If more than one computer shares a modem then the traffic will slow down for each computer if they each request web information at the same time. The same is true for information broadcast from a base station: the more users that are drawing information at the same time, the slower information will be transmitted. When the 802.11b standard was introduced it had a potential bandwidth of 7 Mbps (even though it was advertised as being 11 Mbps). But this is even less efficient as the hubs and switches reduce this further and then it is only half duplex so you have to halve the data rate again. It is no wonder then that once more than a couple of people start using a wireless network operating on the 802.11b standard that time delays become considerable and the 11Mbps in reality is reduced to less than 1Mbps in practice.

The 802.11a and 802.11g standard has the capacity of 54 Mbps, (somewhat confusing when the 802.11a standard has a higher capacity than the 802.11b standard!), while the 802.11g standard has a theoretical bandwidth of 108 Mbps. Obviously the higher the data rates the more computers you can have accessing any one base station. Most school-based computer network systems have a capacity of 100 Mbps.

It is important to realise that each computer is not only receiving information from the Internet over this system but also is sending information to the printers, file servers and other computers connected to the wireless network, and so traffic speeds can be quickly reduced by an increased number of computers using any given base station.

Radio waves can travel a considerable distance if there are no objects in their way. However schools usually are not large open warehouse spaces and concrete, brick, timber and plaster all act as a barrier to radio waves. Also many new buildings use foil backed plasterboard which can create a considerable barrier to radio waves. Because of this it is very difficult to give precise distances over which base stations are able to broadcast. Interestingly water is highly absorbent when it comes to the 2.4 GHz frequency and people are really just walking 2m water towers and can cut down the transmission rates considerably!

For this reason we encourage schools to ensure that they get an independent test done of any area under consideration for use as a wireless zone, making sure that this is done under normal working conditions and not while students are at lunch or on holiday. The test is very simple to do and can be carried out very quickly and should not be expensive.

Wireless base stations using the 802.11a standard can usually broadcast over a distance of approximately 15-20m, while those using the 802.11b standard can broadcast over 20-50m, and should you aspire to the 802.11g standard you will have a potential broadcast distance of between 25-100m.

The number of users that can be connected to any given base station will depend primarily on how much data each individual user is drawing from the network. Based on the average user requiring 1.2Mb/s of data then an 802.11a/g standard system could accommodate up to 50 users whereas an 802.11b would accommodate 10users at any given time. This however is only a guide and is very dependent on what the users are doing and how much data they require.

standard	frequency	bandwidth	Coverage (m)	Users/base station	zones
802.11a	2.4GHz	54 Mbps	15-20	40-50	12
802.11b	5GHz	11 Mbps	20-50	7-10	3
802.11g	2.4GHz	54 Mbps	25-100	40-50	3
802.11n	2.4GHz	108 Mbps	50-?	75-100	?

Care in designing a successful wireless system for your school will ensure that there are no "dead zones" and that there is no overlapping of zones with the same frequency causing interference and corruption of the wireless signal. It is imperative that an assessment is made of the area(s) that you intend to have as wireless zones to ensure that the standard that you are about to deploy will provide coverage across the entire area and at a satisfactory speed within which students and teachers can work without getting frustrated. .

You also need to have the areas concerned scanned to find out whether or not there are other devices operating in this frequency range that could possibly interfere with your wireless reception. Ensure that this scanning takes place over several days and 24 hours a day. You do not want someone coming home at 7:30 p.m. each night, electronically opening the garage door and crashing your network which then has to be reset the following morning.

The location chosen for your base station(s) will have considerable impact on the subsequent reception to wireless traffic. You also need to ensure that people driving past the school can’t sit in their car and use your network to access the Internet (see security section below).

There are some major issues with the security of wireless networks. As was mentioned in the introduction, a wireless network is composed of radio waves sent out from the base station and anyone who has a network adapter which can access the frequency being used could theoretically access your network. It is possible to encrypt data being transferred across the network. Another downside of this is that the speed of delivery will be reduced. There are three different standards of data encryption: 40 bit, 128 bit and 256 bit encryption. 802.11b/g. both come with the capability for encryption (Wireless Equivalent Privacy Protocol WEP), but it needs to be activated! This encryption is not perfect but it will keep out 95% of casual intruders. For most school data 40 bit encryption would be sufficient and still will not slow down data transfer significantly. Teachers using the network may wish to encrypt using 128 bit encryption for added security when using sensitive files such as health, assessment or school finances.

Many wireless suppliers are now providing a firewall security package built into the hub/base station and this is a good option for schools. Suppliers are also supplying integrated “solutions” that have ADSL, VPN, router, firewall, 1802.11g, 4-8-12 switch . . . . all in one small unit, for several hundred dollars.

It is also recommended that your wireless system is password protected so that someone coming into the school cannot access the network unless supplied with a password and userID. The network should also be firewall protected which will stop the scanning of ports in order to pick up appropriate access frequencies and settings.

There are some minor health issues associated with the transmission of radio waves that really need to be kept in context. A wireless base station emits approximately 30 mW of power and is placed in a cupboard or in some other inaccessible location. A mobile phone emits approximately 600 mW and is sitting right next to your brain! However students are in the wireless network for quite a few hours a day and a mobile phone may only be operable for minutes a day rather than hours. For this reason is important that wireless capable notebooks are kept on a desk rather than on the lap of the user. Other than this issue there are no known safety concerns in regard to using wireless systems.

The next-generation of wireless will inevitably involve the use of 3G (3GHz range) systems in conjunction with the use of Bluetooth (for short distance transmission of data). 3G systems require considerable infrastructure similar to the present mobile phone infrastructure and many companies will leverage market share off present locations/equipment in order to distribute 3GHz.

3G systems will be global (Wide Area Network WAN) rather than local systems (Local Area Network LAN). Because of the expense incurred by companies to purchase 3G spectrum licenses, and the infrastructure that this requires to enable it to be distributed we would expect the delivery of high bandwidth access using the 3GHz bandwidth to be quite expensive. In fact it is possible that significantly improved satellite technology will in fact make the cost effectiveness of the 3G systems marginal in favour of satellite delivery.

Wireless networks have a serious role to play within school systems and have reached a point now where they are practical, cost-effective and are consistent with the second education paradigm. For this reason we would encourage schools to investigate the suitability of a wireless installation based on the layout of their buildings and their need to extend the present range of their network or if they consider the advantages that wireless networking offers, considering the investment in base stations and wireless network adapters required. It should be noted that almost all notebooks being sold now have wireless network adapters built-in as either a standard or optional component. For most situations we would encourage the standard 802.11g

Small schools will particularly benefit from this technology as there would be very little difference between this cost between the setting up of a traditional wired LAN and installing a wireless network but do have all the variables tested before committing to this technology.