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Cisco's 'Enhanced Power Over Ethernet': Intentional Design Or Happenstance Feature?

To understand it as Cisco tells the story, you might presume that its "Enhanced Power over Ethernet" was designed on the drawing boards many moons ago. For those not familiar with "Enhanced PoE," it's Cisco's nomenclature for the ability of some of its switches to provide power beyond the IEEE 803.3af standard of 15.4 W. New 802.11n access points with two dual-band radios and 3x3:2 or 2x3:2 MIMO configurations (a MIMO device with two transmit and three receive antennas supporting two spatial streams would be referred to as "2x3:2" MIMO, following a "TxR:S" convention) consume substantially more power than their 802.11abg brethren. Cisco states that its Aironet 1250 access point can consume up to 18.5 W, far beyond the maximum IEEE 802.3af specification of 12.95 W at 100 meters. One way to use less power is to turn off one of the bands, for example, just use 5 GHz. Competitors support similar approaches, as well as turning down radio chains or reducing transmit power, but all of these handicap the full potential of the access point. A new standard for power over Ethernet, IEEE 802.3at, is being worked on that should be able to deliver at least 30 W of power, but it's probably a year or more from final ratification and even longer for broad availability of products compliant with the standard.

Even though Cisco offers a standalone power injector and its 802.11n AP can take advantage pre-standard 802.3at midspan injectors, Cisco decided to leverage its newer Ethernet switch product lines and is marketing "Enhanced Power over Ethernet." In short, these switches are able to supply power beyond 15.4 W, up to 20 W in some cases. Reading between the lines it appears that this proprietary feature is more likely a byproduct of new components than an intentional design requirement. If Cisco had been deliberate about it, the company would have likely built switches and blades that complied with the draft version of the 802.3at standard. Instead, it appears it is taking advantage of the more robust PoE components that found their way into their new 3750-E and 3560-E desktop switches, and Catalyst 4500 E-Series and Catalyst 6500 Series chassis switches. Even if I assume that Cisco intentionally installed more powerful PoE components in their new Ethernet switches to meet the Aironet 1250's anticipated power requirements, the fact that Cisco hasn't completed the IOS software support for these newest switches raises some suspicion that the "Enhanced Power over Ethernet" is a last-minute feature requirement by the wireless networking business unit. When Cisco initially announced its "Enhanced Power over Ethernet" last fall, it was targeting a December code release, but that slipped to February for its desktop switches. Cisco doesn't have the necessary software ready for its chassis switches.

Unsurprisingly, Cisco's implementation of "Enhanced Power over Ethernet" is proprietary and designed to enhance sales of its own switches. It depends on Cisco's proprietary link layer protocol, CDP (Cisco Discovery Protocol), rather than the IEEE's 802.1AB, also referred to as LLDP. Using CDP, the Cisco access point can communicate with the Cisco switch to request more power. Cisco would call this "innovating beyond the standard to meet customer demands," which it is, but this time around it will be unable to claim that it's providing a solution for standards that don't yet exist -- pre-standard 802.3at power injectors are available. From a technology position it's fortunate for Cisco that its newest switches can exude greater power, but it's no time to suggest that "Cisco has been promoting the evolution of technology to standardization" while at the same time restricting access to that power only for its own access points. Of course, it's every vendor's prerogative to grow market share, and Cisco's unique position in owning both wireless access points and switches and dominant market share in each category allow it to offer closed solutions despite developing standards.

So don't let Cisco's "Enhanced Power over Ethernet" paint your enterprise wireless plans into a corner. Cisco shops eager to deploy 802.11n draft 2.0 product can use pre-standard 802.3at midspan injectors or Cisco's own power injector. Cisco's competitors are offering standards-based powering option. Meru hasn't pulled any punches and recommends that its customers use local power or pre-standard 802.3at power injectors. Those who have their eyes set on Aruba should wait until it ships its 802.11n APs in volume. Aruba claims that its 802.11n draft 2.0 AP runs on standard Cat5e cabling within 802.3af specifications. Siemens' similar claims have been (at least initially) validated by the Farpoint Group. Trapeze is likely holding out on shipping its long-previously announced product until it has it working within 802.3af specifications, too. Only Xirrus, with its unique array, requires a proprietary PoE solution.