Following on from last month's article (AJ 16.03.06), Gardiner & Theobald's Information Communications and Technology (ICT) specialists provide an overview of wireless technology and the important factors that the architect needs to consider when designing a building.
The main difference between a 'wired network' and a 'wireless network' is that a wireless network uses high-frequency radio waves rather than wires to transmit data, minimising the amount of hardwiring required.
HOW DO THEY WORK?
Electromagnetic radio waves are used to transmit data between devices. The data is translated into radio waves and then reconstructed at the receiving end back into data. In a typical office network configuration, a radio transmitter/receiver (a 'wireless access point') is attached to a standard data outlet fed by Cat 5 or Cat 6 cabling as part of the cabled local area network (LAN), which acts as a radio gateway on the cabled LAN.
The end device, normally a desktop PC or a laptop, will have a radio network card that replaces the wired network card. The only physical difference between wireless and cabled networks is the link between the end devices and the network.
The bandwidth (the amount of data that can be transmitted over communications lines at one time) offered by each access point is shared among all the connected users in much the same way that old Ethernet hubs provided shared network bandwidth. This means that as the number of connected users increases, the throughput performance decreases. An 802.11b access point with an effective maximum bandwidth of 6Mbps could support 12 users at broadband speeds of around 512kbps in ideal circumstances. An 802.11g access point offers the potential to support more users at comparable speeds as long as all users have devices that can connect with the 802.11g standard; if any of the users sharing the access point connects at only 802.11b then all other users are also restricted to a lower performance level - that is how the wireless technology maintains compatibility with both standards.
Throughput performance also decreases as the radio signal attenuates or weakens. This happens as the distance increases between the client device and the access point. In a clear line of sight, the throughput will fall to about half of the effective maximum at 30m, and will fall to about 10 per cent of the effective maximum at distances approaching 100m.
PROS AND CONS Wireless networks offer greater exibility, as end devices (PCs, laptops, printers, etc) are not restricted to physical network points.
Of-ce-based wireless employees can be networked without sitting at dedicated desks/PCs. There is a reduction in capital expenditure because of a reduction in cabling and associated installation time;
also operational expenditure is reduced as there are fewer devices to maintain. This type of networking can be easily retro-tted into an existing office with minimal disruption.
The main issue with wireless networks is security. They are more vulnerable than traditional wired networks, as radio waves are easier for hackers to intercept. They are also susceptible to interference from other third-party radio waves (police, emergency services, mobile-phone operators, etc), people and objects. System range can be affected by building materials - for example metal studs and steel reinforcement bars.
EFFECT OF BUILDING MATERIALS Materials will either reduce the signal strength, reect the signal, or diffract the signal (see diagram above).
Some of the most common materials used in construction are listed below, together with their radio-magnetic absorption properties:
aluminium - less than 50 per cent absorption drywall (two layer) 50 per cent absorption dry plywood 50-70 per cent absorption brick-poured concrete 50-70 per cent absorption steel >70 per cent absorption.
These materials will reduce the range of the wireless network and decrease data-transfer rates for any devices connected to it. This can result in intermittent signal reception and a reduction in performance. It is important that the network is designed by a professional company to ensure that adequate transmitters are purchased and located evenly around a building at optimum locations.
Part L of the Building Regulations now includes regulations covering the new window energy ratings (WER).
Metallic coatings on glass are commonly used to meet these guidelines, which are useful for the security of wireless networks, but cause problems with wireless LANs (WLANs). The glass basically acts as a layer of screening between the office and the outside world. This will not prevent all signals from transmitting through the glass, but will greatly reduce the signal strength and will make it much more dif-cult to receive signals inside the intended area.
One downside of this is that wireless 'hot spots' cannot be created outside the fabric of the building without using external access points. This may be a disadvantage if wireless coverage is required across a company campus with open grass areas that may be used during the summer as breakout spaces.
The number of users will determine the minimum number of access points required. Since each access point transmits equally in all directions, consideration needs to be given to the following:
redundancy to avoid black spots (an area where reception is extremely weak or non-existent) if an access point goes ofine;
corners (especially those less than 90º);
pillars (these will create 'shadows' in the coverage); and volume of data (for example, architects' drawings require a higher bandwidth [speed] because of the size of CAD -les).
A useful analogy is to consider each access point as a lightbulb. However, each user/end device connected to the network will absorb the 'brightness' of the closest lightbulb by about 10 per cent.
WHAT ARE THE COST DRIVERS?
The main cost drivers include:
number of end users (assume a maximum of 10 per access point);
type of construction material used in the building;
bandwidth required for users;
size, shape and layout of the building; and oor/desk layouts.
The standard colours of access points are grey, cream and black. Other colourings will add to the time and expense.
The table (above) provides a simplistic method of costing a wireless network (excluding servers and desktop equipment); it also provides an indication of the cost differential between a fully hardwired network and a partial hardwired network with wireless networking.
CONCLUSION Going wireless may require upgrading of all end devices if installing to an existing building.
Visiting guests may not have wireless-enabled devices.
Building architecture may not be suited for wireless networking.
Security risks may mean data is too sensitive to risk transmitting over the open airwaves.
Wireless networking still has a long way to go to beat the speed of a wired network.
The optimum building design for wireless networking at the moment is square, with no internal walls or columns, and made entirely of plastic? This series of articles and online briefings will cover various aspects of designing for ICT. Visit www. ajplus. co. uk/ict Forthcoming articles in the AJ will cover:
case study on a major building;
office buildings; and retail buildings.
Online briefings will deal with:
desktop technology; and