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Ofcom works out why Wi-Fi doesn't work

Four times faster in Bournemouth than London?

The smart choice: opportunity from uncertainty

An Ofcom-commissioned report into Wi-Fi performance concludes that it's baby-listeners and TV-senders that are mucking with the signal, not to mention the "Free Public Wi-Fi" virus, without which we'd all be connecting faster.

Ofcom's remit is to ensure efficient use of radio spectrum, including the unlicensed 2.4GHz band used by Wi-Fi. To that end, it commissioned specialist consultancy Mass to examine how effectively the band is being exploited.

What Mass discovered (pdf) is that while Wi-Fi users blame nearby networks for slowing down their connectivity, in reality the problem is people watching retransmitted TV in the bedroom while listening to their offspring sleeping, and there's not a lot the regulator can do about it.

Outside central London that is: in the middle of The Smoke there really are too many networks, with resends, beacons and housekeeping filling 90 per cent of the data frames sent over Wi-Fi. This leaves only 10 per cent for users' data. In fact, the study found that operating overheads for wireless Ethernet were much higher than anticipated, except in Bournemouth for some reason: down on the south coast 44 per cent of frames contain user data.

The following table shows the proportion of frame types around the UK, listed by population and demonstrating that it's not the number of locals that defines the speed of your wireless connection.

Wi-Fi Frames by type and location

The bigger version is more legible

Beacon frames are those sent out by access points, advertising their presence, or by computers that have picked up the "Free Public Wi-Fi" infection - originally considered to be a Windows thing but observed on Meamo too. Users see an access point of that name, and attempt to connect, only to find themselves advertising such a point to everyone else. What's worse is that it seems "Free Public Wi-Fi" points are sending out beacon frames ten times more frequently than they should (every 0.01204 seconds), leading to a significant amount of traffic:

"Walking around central London one can expect to encounter, on average, 26 of these devices per hour. On average they constitute about 7% of the total frame density, but this is very much an average and this peaks at about 28% in some cases"

But even that's nothing compared to the interference generated by analogue baby listeners and other deregulated kit, and the report notes that much of the overhead traffic shown is generated by devices reconnecting when they've lost a connection. Mass also demonstrated, in laboratory conditions, how a baby-listener can generate a swath of interference in such a way that devices could see a nearby access point, and report a strong signal, but couldn't connect because the interference was so great - a situation that could equally result in an slow or unreliable connection that the user would struggle to solve.

Not that bad Wi-Fi is always to blame - Mass found that users are quick to blame the wireless part of their connectivity when the fault actually lies in ADSL, routing or even the servers at the other end of the connection. Mass also found that, contrary to expectation, residential users were good at changing the Wi-Fi channel, though pointed out that once 802.11n devices start to use bonded channels the chances of interference will increase.

Dealing with the interference from perfectly-legal AV transmitters and baby listeners would seem to yield the greatest increase in capacity, not to mention reducing the headache of managing residential wireless, but it's a hard thing to do in unregulated spectrum. Baby listeners are already moving towards digital transmissions, and some even come labelled "Wi-Fi friendly" to indicate they'll slot into a single 802.11 channel (5MHz wide, rather than the 8MHz channel used by analogue listeners which ensures any interference spans two channels).

But while ever-cautious parents will pay a premium for the digitally-rendered sniffles of their beloved, not to mention additional features such as a back channel, thermometers and the like, cheap AV senders have no compelling reason to go digital and show no signs of doing so. Enforcing Wi-Fi friendliness would be unpopular, and difficult, within an unregulated channel, but the alternative is to continue suffering intermittent connections so that Sky customers can watch TV in the bedroom. ®

Mobile application security vulnerability report

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