Netgear admits wireless speed claims are misleading

Nasty Wi-Fi precedent

channel

Comment The real question in the Netgear class action case is why it only applied to NetGear, given the absurd figures quoted by all Wi-Fi hotspot providers.

The company has promised a 15 per cent discount to US users, who claim they were misled by advertising - but which Wi-Fi outfit doesn't mislead?

In the case of Netgear, its claim was that the RangeMax Wi-Fi product - which uses a pre-N style of MIMO wireless, was capable of reaching 240 megabits - a claim it now modifies with "Actual performance may vary according to the operating environment."

Netgear says that it accepts no liability for the misunderstanding ("liability" being a technical term in legalese) but it could well complain that it's hardly unique.

Rangemax claims graphIt's most vulnerable on the analysis that if you take a MIMO wireless out into the open, it gains nothing. Most Wi-Fi technology is actually badly impeded by what is called multipath - the fact that the wireless signal bounces off obstacles, generating another reflected signal which confuses the receiver.

MIMO actually uses the multipath signals to increase throughput. Logically enough, if you are in an environment without reflections, you don't get multipath, and MIMO is useless.

But NetGear isn't the only Wi-Fi provider to make exciting claims [see graph, above right] about MIMO. Belkin's publicity for its Wireless pre-N router [see picture, top left] quite flatly says "8x greater coverage than standards 802.11g" and "6x greater speeds than standard 802.11g." If that isn't misleading, it's hard to see why not. A clearer expression would be "under ideal circumstances" but in fact, even then, you'd get the impression that this is going to run faster than 100 megabit Ethernet.

In reality, the typical user won't come close.

The problem of Wi-Fi traffic speed isn't just the common Ethernet one - if you share a medium, the maximum throughput can't ever be reached. It's endemic to the Wi-Fi business that people claim data speeds which have nothing to do with the real world ability to transport data.

The technical term is "payload" and it refers to the number of bits transmitted which belong to the user, rather than to the wireless equipment. The trouble is, the Wi-Fi standard steals an awful lot of the bits.

To quote the excellent Norwegian academic and research network, UNINETT: "Transmitting the data is not just burping out a bunch of signals on the air. A strict set of rules is governing the way a transmission should behave (CSMA/CA). First the sender has to wait a period of DIFS (Distributed Coordination Function InterFrame Space) time of 50 Usec before the channel is presumed clear of traffic. Then a Data Frame or a Request to Send frame can be sent. The receivers answer to this is with an ACK or Clear To Send, accordingly. The receiver has to wait a SIFS (Short InterFrame Space) time of 10 Usec before this reply is sent."

Anybody who describes ordinary Wi-Fi as carrying 11 megabits per second is, technically, correct. But the payload on 802.11b is half that; 5 megabits - and that's shared amongst all users. Also, the rate drops as you move away from the access point; 802.11b drops back to one megabit when the signal gets weak.

As a rule of thumb, if you take the Wi-Fi standard bitrate, you can work out the payload easily enough by dividing by two. Rarely, it will be faster; usually, a lot less. Put two access points on the same channel in the same area, and it can be so much less you may even wonder if you're connected.

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