A MaxResponse Guide

Eeny meeny Mi Mo

Evolving WiFi

You may have seen that a new generation of WiFi products are being pushed by some manufactures - notably Belkin, Netgear, D-Link and Linksys. One is called Super G and claims to double the transmission rate whilst the other is Pre-N which claims both to increase the range and maintain a constant data transfer speed.

As you may recall WiFi devices - which includes Apple's Airports - conform to international standards know as 802.11 with three suffixes (a), (b) and (g). 802.11a was the first to be ratified but wasn't taken up by many since it had a limited range and used the 5Ghz radio spectrum. 802.11b was the basis for the original Airport and had a maximum throughput of 11Mbps in the 2.4Ghz band, following this was 802.11g which also used the 2.4Ghz band but upped the speed to 54Mbps it was also backwards compatible with (b) which meant that you could used a mixed network of original Airport and Airport Extreme. Super G is a development of this standard in which two separate channels are bonded together to give a max speed of 108Mbps.

The drawback is that when you are using a mixed network of (b) and (g) devices the speed drops since the data packets for the (b) devices take up more of the bandwidth since they take longer to transmit and receive.. So if you retain an old iMac, for example, which uses an Airport card on a Airport Extreme network you won't achieve the highest speed for the (g) devices.

You may notice that I have been careful to say a maximum speed, in fact the speed depends on a number of factors and the handshaking between the BaseStation and the various Airport cards will determine the actual speed at which the network will run, on a (g) network the steps are 54; 48; 36; 24; 18; 12; 11; 9; 5.5; 2; 1 Mbps. So, if you have a computer at the very edge of the useable range you may find that the actual data rate is no where near the optimum even though everything is equipped with (g) adapters.

It is also worth remembering that the actual data throughput will be a lot less than the quoted 54 or 11 Mbps due to the signalling overheads involved. On a (b) network the maximum real data transfer is likely to be somewhere between 3-4Mbps and on a (g) network 27-35Mbps, the lower figure is if TCP is being used which adds its own overheads

Pre-N device manufactures are trying to guess what the standards committee will recommend when it presents its conclusions in 2006. It is likely that these will include multiple smart aerials as well as multiple transmitters and receivers using a technology known as MIMO (Multiple Input Multiple Output) to increase the range and maintain a constant data rate.

Some manufacturers are also producing dual band devices using both (a) and (g) claiming that the (a) band is less prone to interference and with bonded channels can give speeds suitable for video streaming.