802.11n won't happen overnight

Faster Wi-Fi is on its way - but it needs more electricity. Could that delay it seriously in business?


Despite the hoopla, fast Wi-Fi, using the 802.11n standard, scarcely exists in the enterprise. This week saw what is, in fact, the first 802.11n installation in a European campus, put in by the comparatively minor player Meru.

This is after a year in which all enterprise Wi-Fi vendors have promised 802.11n equipment (eg Cisco, Aruba, Trapeze),
the Wi-Fi Alliance has begun branding the latest draft of the new standard, 802.11n laptops have gone on sale, and 802.11n access points have taken the home market by storm (they already had 15% of that market in 2006).

With all that is going on, enterprise Wi-Fi vendors started such a consuming debate on how to install and power Wi-Fi access points, that one might have got the impression they were actually in widespread use.

In fact, no-one expects much activity on 802.11n installations until the middle of 2008. "It's a natural process," says Richard Webb, wireless analyst at Infonetics Research. "Nothing gets widespread adoption immediately - except amongst consumers." Rolling out 802.11n would mean a big upgrade for customers who already have full Wi-Fi coverage, and would be a complex add-on to existing wired networks, for those who haven't.

In keeping with that leisurely timetable, Cisco has detailed specifications for its 1250 access point online, but Trapeze and Aruba don't - because they aren't shipping them in anger yet.

So, what are the issues?

Power consumption

802.11n installations will use two bands - and that means the access points will need more power. The 5GHz band has been almost untouched, because 802.11a has been largely ignored, but this will have to change, because only the 5GHz band gives enough channels to operate 802.11n to its full potential. However, 802.11n networks wll have to also operate on the 2.4GHz band - to support the millions of existing 802.11b and 802.11g clients.

The power demand of dual-band systems radios is more than the power offered by today's 802.3af power over Ethernet installations, so using full-fledged dual-band 802.11n means running an extra power supply (or an extra Ethernet cable just for PoE) to each access point. This is a big deal because the majority of the cost of an access point is in the installation, and having to run an extra power cable can more or less double that.

Things will get better. Successive versions of the 802.11n silicon will use less power as more components are integrated. Meanwhile, the IEE is working on 802.3at PoE Plus (power-over-Ethernet specification), which will be able to offer around 56W of power over Ethernet - which will be plenty.

But 802.3at won't be completed for a year (there's a draft out now), so vendors have to do something in the meantime.

Cisco has its own proprietary interim technology: "During the design of our AP 1250, we worked very closely with our switching business units to make sure that we had designed an solution that could be powered over Ethernet," says Pat Calhoun, the chief technology officer of Cisco's wireless technology group. "While Cisco would have preferred to use 802.3at, the standard is not expected to be ratified until end '08/early '09, so we needed to design our own interim solution."

Cisco's system puts more power into the Ethernet - as long as the equipment both ends is Cisco's, otherwise it falls back to standard 802.3af so other equipment can still be used. "This is not a standard interface and we recognise this is not optimal, which is why we are working the standards angle hard to accelerate the process," says Calhoun. "The paramount goal for Cisco on this topic is to ensure that customers have very clear guidance and to address this with a clear solution that combines simple deployment and optimal performance. Letting customers make investment decisions only to find out later on that their network is operating at a lower performance is less than ideal."

Other vendors reckon that a proprietary solution will be an expensive lock-in, so it's best to get by with less power till 802.3at comes in.

Trapeze offered the option of using two Ethernet cables to power its access points - many businesses do have spare switch ports, so that may be cost-effective. Aruba's AP 125 also has two Ethernet ports, both with PoE, so it can presumably do the same thing.

Aruba has talked about building in a fall-back, so that if there isn't enough power, the radios will work in a format that uses fewer antennas. But Aruba also said that, in practice, many 802.3af installations can just about deliver enough power for dual-radio APs (apparently 17W is enough and, while this is outside the spec of 802.3af, it is apparently feasible for a lot of installations). Cisco's Calhoun doesn't like the sound of this: "Trying to push more power over 802.3af can actually be a hazard," he says. Trapeze isn't pushing this option, but because the two companies use the Wi-Fi silicon, the company has said it can also do whatever Aruba can.

Aruba and Trapeze both use Atheros silicon, while Cisco uses Marvell (we are told). There doesn't seem to be a significant difference in the power demands, from the limited information on the companies' data sheets.

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