Draft-N routers hobbled in cities

Many Draft 11n routers and access points on sale today will run at only half speed if used legitimately in cities, the managing director of the Wifi Alliance has admitted.

One of the advantages of 11n is that it can use 5GHz bands, which are less crowded and have more channels than the 2.4GHz frequencies most used by Wifi. The older 11a can also use 5GHz, but 11n performs better over a longer distance.

Intel’s new Santa Rosa notebook platform supports 11n at both 5GHz and 2.4GHz, yet most of the routers and access points available now support only the lower frequencies – and, for reasons rooted in industry politics, this can affect performance.

About half the claimed top data rate of 11n stems from the fact that it allows the channel’s bandwidth to be doubled from 20MHz to 40MHz. This is rather like using two lines instead of one on a crowded switchboard, and it caused a huge row in the standards committee, even though some ‘turbo’ versions of Wifi 11g already do something similar.

Critics pointed out that at 2.4GHz there are only three non-overlapping channels (sets of carrier frequencies), so anyone grabbing two of them is hogging the airwaves.

A compromise was reached, whereby 11n would default to 40MHz channels at 5GHz, where up to 12 channels are available. But at 2.4GHz, a device should switch automatically to 20MHz channels if other Wifi networks are in range.

As there are usually Wifi networks within range in cities, this means devices should usually default to half-speed. Users can override the default and PCW has been told that some manufacturers supply devices using 40MHz channels by default.

Frank Hanzlik, managing director of the Wifi Alliance, which has started certifying Draft-N products, said: “No device that does not default to 20MHz at 2.4GHz could carry our logo.”

He agreed that some of the claims on product boxes could be misleading, especially for city dwellers. “There has been too much competition to do with the biggest number. People feel compelled to offer the 40MHz speed on the box.”

Tunji Akintokum, Linksys country manager for the UK and Ireland, confirmed that all his current Draft 11n products operate only at 2.4GHz, though 5GHz versions are mooted for the end of the year.

He said its WRT150N router operated a “good neighbour” policy of defaulting to 20MHz channels, but the more expensive WRT300Nv2 and WRT350Nv2 did not implement the policy. He was unable to confirm as we went to press whether this meant they use 40MHz by default.

Contention between wireless networks is likely to get worse because of the increased range of 11n and its projected use for streaming video. Intel is beginning to address interference issues and Hanzlik said: “I’m sure we’ll have a technological fix before they get serious."