With wireless local area network (WLAN) deployments approaching "hockey-stick growth", many users are looking to improve their installations - from security to performance perspectives.
Andy Robb, a technology specialist at Duxbury Networking, looks at how to improve the physical attributes of a WLAN.
Wireless local area networks (WLANs) are today characterised by a mixture of intelligent access points, thin access point/wireless switch architectures - some with centralised management and security capabilities - mesh routing in network backbones and other performance-oriented technologies and components.
But no matter what technologies are in use, one factor that is common to all WLANs is the need to optimise the wireless signal through careful placement of critical components, such as antennae, to avoid obstacles and reduce interference.
A good place to start, apart from ensuring all antennae and cables are secured, is to ascertain which wireless devices are transmitting the heaviest loads and in need of assistance.
Some manufacturers have automatic data rate fallback functionality in their products, which allows increased distances to be achieved between devices without losing connectivity.
The downside is that devices further away from one another are inherently slower than those situated close together.
Therefore the most critical links in the network are those where the traffic is highest, and the distances are greatest.
Positioning antennae
To optimise performance, antennae should be in line-of-sight of one another, in high positions and clear of obstructions.
Keep antennae around 7 500mm away from metal fixtures such as sprinklers, pipes, metal ceilings, reinforced concrete, metal partitions. And keep them clear of large water containers, such as fish tanks and water coolers.
Antennae transmit weakly at their bases, where they connect to the device they support. So if an antenna is mounted vertically, it is important to avoid the weaker signals heading downward from routers and access points.
If an antenna is situated on the second floor of a building, yet serves as a link to the first floor, face the antenna downwards.
For multi-story buildings, placing antennae at 45 degrees (diagonally) or parallel to the floor may be the most effective.
Performance
To reduce `noise` or interference, it is also best to place antennae away from various electromagnetic noise sources, especially those in the 2 400 - 2 500MHz frequency band. Common noise-creating sources are computers, fax machines, copiers, cellphones and microwave ovens.
From a performance perspective, using the optimum transmitting channel supplied by the WLAN device is key.
Devices that transmit powerfully - such as routers, access points and cellphone base stations - confuse one another, so it is important to (firstly) distance them and then to have them use different channels.
For WLANS based on the 802.11b and 802.11g standard, there are 11 channels to choose from in SA. (There are 13 channels available in Europe.)
Obviously, when there is little interference to be considered, any channel choice is possible. But when interference is a factor, particularly from overlapping WLANs, each network should use one of the non-overlapping channels: 1, 6, or 11. Then, three networks can use the same space with minimum interference. If this is impossible then channels should be as widely spaced as possible.
Unfortunately, interference cannot be avoided simply by using other channels. Wireless protocols 802.11b and 11g only have three non-overlapping channels available to them, so when four or more channels are used in the same area, the level of interference can increase notably.
Options would be to place routers and access points further away from one another or place physical barriers between them. Directional antennae are also a good purchase choice for use in these cases. It may also be useful to keep part of the network wired.
When all else fails
Interference and noise are the most effective WLAN performance inhibitors. So, if it is not possible to obviate the noise, it might be advantageous to reduce the amount of network data being transmitted - and lower your expectations of the WLAN.
One way to lower data transmission and overhead is to disable the WLAN`s SSID (Service Set Identifier) broadcast. The SSID is a unique 32-character identifier attached to the header of packets sent over a WLAN that helps equipment to find the strongest signal.
When the SSID is broadcast, neighbouring WLANs and associated equipment keep a record of it, and automatically try to connect several times a second; this can cause significant performance reductions.
However, turning off other broadcast services - such as WEA (Web-Based Enterprise Management) and WEP (Wired Equivalent Privacy) - may well increase throughput, but also significantly increase the WLAN`s exposure to hackers, with disastrous consequences. Be cautious.
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