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Cisco's 802.11n AP Announcement Confirms and Surprises
The most unexpected element of Cisco's news is that they will be able to power their dual-radio 802.11n access points using selected models from their Catalyst line of switches.
September 06, 2007
Cisco's announcement that pre-802.11n Draft 2.0 access points will be available for ordering in October makes for something of anti-climatic announcement. This access point is the only enterprise-focused vendor-branded access point in the Wi-Fi Alliance's pre-802.11n Draft 2.0 certification test bed, announced in mid-May. On the other hand, more than half of the enterprise WLAN vendors have already announced 802.11n product and some are shipping. Ironically, Cisco will likely be the first enterprise WLAN vendor to ship a Wi-Fi certified access point. Only Extricom, Motorola (formerly Symbol) and Siemens have yet to make a public statement regarding their 802.11n plans.
Cisco's Aironet 1250 is a modular access point, with the first instantiation a dual-band/dual-radio access point supporting 802.11n on both radios. It can work in either unified or autonomous mode, exactly like the currently shipping 1240-series access points. Historically, this is Cisco's second modular access point (the first was the 1200) but this one is field upgradeable. According to Ben Gibson, Director, Mobility Solutions Marketing for Cisco, early adopters wanted modularity for flexibility and investment protection. While the final 802.11n standard is still months away from final ratification and no vendor has promised compatibility with the final IEEE standard, and although there's no reason to believe the final standard will require modification of the PHY, it appears that Cisco's customers are hedging their bets. There will be additional service modules in the future, but it appears that exact configurations have still to be decided and Cisco was reluctant to share details. The only item that was suggested was a spectral analysis module, likely a product of Cisco's relationship with Cognio.
The most unexpected element of Cisco's announcement is that they will be able to power their dual-radio 802.11n access points using selected models from their Catalyst line of switches. According to Ben Gibson, tests are showing that their new APs consume power in the range of 18 W, but the IEEE 802.3af standard dictates 15.4 W of power output at the switch port, which drops off to 12.95 W by the time it reaches the powered device due to cable losses. Cisco appears to be in the fortunate position to have engineered enough capacity in the original components and control of its settings that it can boost the output power on at least a subset of the switch's ports. Cisco will use CDP (Cisco Discovery Protocol) to facilitate the power negotiation between access point and switch. Cisco will announce at later time which 3750, 4500, and 6500 series switches and blades will support this capability, and offer software later this year to enable it. It's not known what percentage of deployed PoE ports in edge switching closets support this 'boost' feature (for example, this appears to exclude the Catalyst 3560, a popular desktop switching product), but the ability to boost at least a subset of the ports clearly gives Cisco shops a leg up over the competition. Others will have to resort to operating APs with less than full capabilities, adding a second PoE power source, installing a separate midspan power injector, or accessing a local AC power supply.
Cisco also shared some preliminary performance numbers based on pre-announcement trial deployments. Sites have seen rates of 120, 130, and even has high as 138 Mbps per radio. While this is likely in a greenfield environment without the debilitating effects of legacy clients, these claims did exceed by a large margin those privately demonstrated by both Meru and Trapeze at Interop Las Vegas. Cisco also performed some systematic testing with Intel, a significant leader in enterprise Wi-Fi clients via its Centrino line or products. Their white paper documents average rates at close range was just shy of 147 Mbps with a 40 MHz wide channel, more than 5 times the 22.5 Mbps they achieved with 802.11a/g. Of course, more clients at farther distances will drag that aggregate rate to a lower number, but it's still significant. More importantly, they measured a two times increase in reliability and predictability, using retry requests as a proxy.
Cisco's dual-radio AP 1250 has a list price of $1,299 (it's another $114 for six of antennas) and with an almost standard 30 points off list, hovers just above the $900 mark. That's within the price range of other vendors and notably less than the $1495 price tag for Meru's 802.11n-capable access point. Gibson stated that non-modular access points would come down the pipe, but made no promises when they would arrive on the scene. Cisco may in fact wait until final 802.11n ratification to bring to market a non-upgradeable access point.