Network giant enhances IEEE 802.3at standard for devices requiring extra power

Network giant Cisco has announced it is not prepared to wait for ratification of the Institute of Electrical and Electronics Engineers (IEEE) 802.3at enhanced Power over Ethernet (PoE) standard, and is moving forward with its own system, called enhanced PoE (ePoE).

The IEEE 802.3at standard – or PoE-Plus as it is also known – has been in development since September 2005 and is due to be ratified later this year. It will cater for devices requiring more power than the current 802.3af standard supplied over standard network cabling.

Cisco has introduced new Catalyst switches and features to its Campus Communication Fabric, a blueprint for network services that will now feature its ePoE system across all Catalyst hardware, beginning with 3750-E, 3560-E and 2960 series hardware.

Firms deploying yet-to-be-ratified 802.11n standard wireless kit may need to upgrade their current 802.3af PoE systems, since these new access points (APs) could require more power than can currently be provided by 802.3af at about 15 Watts.

New 802.11n systems have gigabit network connections rather than the 10/100Mbit/s of 802.11a/b/g APs, and also need to power the new multiple input/multiple output (MIMO) feature of 802.11n radios, as well as the 802.11a/b/g radios themselves. The extra bandwidth and processing requirement of Gigabit Ethernet means that 802.11n systems will also need more power.

Other firms, including comms vendor Siemens – which recently announced its 802.11n system – have said they can provide enough power to their 802.11n APs using switching hardware which conforms to the earlier 802.3af standard. This is a claim that would preclude firms purchasing 802.3at-compliant hardware at a later date.
Pat Calhoun, chief technology officer for the access networking and services group at Cisco, said the power issue was not mainly concerned with the amount of network traffic running through the AP.

“If your Cisco 802.11n AP is connected to a port that can only supply the 802.3af standard 15W, only one radio will actually operate – although you can define which radio you want to use, the 2.4GHz (802.11b/g/n) or the 5GHz (802.11a),” said Calhoun.

Users cannot choose which radio they want turned off when it is operating. “This has to be specified in advance,” Calhoun said. “Unfortunately, because of how 802.11 wireless systems work, dynamically turning radios on and off is difficult.” Cisco has borrowed some ideas from the future 802.3at standard, but maintained compatibility with 802.3af.

“802.3af has a specific way in which it transmits power over the line and we have preserved that,” said Calhoun. “We have used the part of 802.3at standard that is concerned with negotiation between devices, requiring power and the switches that supply the power. We have extended the Cisco Discovery Protocol to negotiate how much power will be required by our 802.11n APs and supply this accordingly.”
Calhoun said he was not aware of any 802.11n chipset available that required less power than that provided by 802.3af systems.