Random 802.11n ObservancesBy CWNP On 08/09/2007 - 10 Comments
The 802.11n amendment allows for up to 4x4 MIMO. That's 4 transmitters and 4 receivers working at the same time. Due to cost, nobody is building a 4x4 system. Instead, we're seeing 2x2 on the cheap stuff, 2x3 on the higher-end client radios and the lower-end APs, and 3x3 on the higher-end APs. More transmitters and receivers means better quality: better reception, higher throughput, the works. Always look for 2x3 stations and 3x3 APs whenever possible.Some systems do not have 40 MHz operation, and while that isn't the only feature that adds to the advantages of 802.11n over 802.11a/g, it's a biggy. To add to the confusion, some systems, like Apple's new extreme basestation only give you 40 MHz operation in 5 GHz, but not in 2.4 GHz...and did I mention that Apple doesn't let you choose your channel in 5 GHz? Grrr. The Wi-Fi Alliance certification test plan says that 40 MHz operation in 2.4 and 5 GHz is optional.
The 802.11n draft specifies up to 4 spatial streams - streams of bits transmitted over separate physical paths. Manufacturers are only building chipsets to support 2 spatial streams currently, and the Wi-Fi Alliance is only requiring certified APs to support 2 spatial streams in Tx and Rx modes and Stations to support 2 spatial streams in Rx only.
If you're planning on installing 802.11n anytime soon, consider the fact that you need a dual-band 802.11n-capable protocol analyzer and/or WIPS. Without these tools, you're flying blind. Connectivity troubleshooting - toast. Performance optimization - no go. Security monitoring - ha! Deploying a WLAN system without the tools to perform troubleshooting, optimization, and security monitoring doesn't make any sense. When will these tools be available?
Wildpackets, AirMagnet, Tamosoft, and AirPcap have given us laptop-based 802.11n protocol analysis, but the most significant hang-up thus far is sparse client radio support. Keep in mind that dual-band is what REALLY matters because half of the picture is more or less no picture at all. Broadcom's Intensi-Fi chipset comes in CardBus format thankfully. You can buy this card from Buffalo Technologies or one of their resellers. So far Broadcom's development department has only just begun to work with most of the protocol analyzer vendors on the market. Thus far they work with Wildpackets, but that's all I can find so far. AirMagnet and Tamosoft are working toward this (as I understand), but Network Chemistry (now part of Aruba Networks), AirDefense, Network Instruments, and Network General, haven't announced anything yet on the dual-band front.
What about the Atheros AR5008-3NX chipset (undoubtedly a market favorite)? The only place I've seen one of these so far is inside an Apple Extreme Basestation. http://www.vonwentzel.net/ABS/Dissection-Extreme-n/index.html I'd love to have the CardBus version of this chipset, but there's nothing available to the public yet. The only vendor saying that it's coming shortly is AirPcap - in September 2007. What about Marvell's 88W8060 chipset or Qualcomm/Airgo's AGN400 chipsets? Nada. The Wi-Fi Alliance seems to be the only organization on the planet to have any of these chipsets in a useable format. So, at present, we're pretty much stuck in limbo. Grrr.