A proposed standard for powering network devices over Ethernet cabling is still a year from completion, but users of IP telephones and wireless LAN endpoints are adopting the technology in the meantime.
Powering an IP phone or wireless LAN endpoint over a Category 3 or 5 Ethernet cable should help make business IP telephony phone systems more resilient and make it easier to set up an 802.11X LAN, because it eliminates the need to run power and network lines to wireless LAN endpoints, experts say.
The technology for running in-line power has been around for almost two years. Cisco Systems Inc. offers blades on its Catalyst chassis switches that can power phones and wireless LAN endpoints via Ethernet cabling, and companies such as PowerDsine make similar products that other switch makers resell.
The IEEE’s proposed 803.3af standard involves delivering 48 volts of AC power to small networked devices – such as IP telephones, wireless LAN endpoints and networked kiosk terminals or video cameras – over four- and eight-wire unshielded twisted pair cabling. In-line power gear, or so-called power source equipment (PSE), can deliver an AC current two ways: over an unused twisted pair of wires – called midspan PSE by the IEEE; or over live wire pairs that deliver data – a method called endpoint PSE.
Powered devices – such as IP phones – and PSE gear communicate via electrical signals that let the PSE detect if a device that can receive in-line power is attached. Delivering 48 volts of AC to a non-802.3af IP phone or wireless LAN box could damage the device.
Avaya Inc.’s Cajun P333T-PWR, a 24-port Ethernet switch that delivers power over Cat 3 and 5 cabling, is in use at the Salvation Army’s Joan Kroc Center, an administrative facility in San Diego. According to systems analyst Ken Suyenaga, the powered Ethernet switches were a requirement when the organization decided to install Avaya’s IP600 IP PBX. Otherwise, IP phones would have to be plugged into outlets at workers’ cubicles and offices, which would leave the phones dead in a power outage. With the redundant P333T-PRWs plugged into universal power supplies it would take two switch failures and two UPS failures to bring down the phone network, he adds.
At the University of Arkansas, Pine Bluff, Cisco in-line power switches have made it easier to deploy wireless LAN endpoints and phones, says Maurice Ficklin, director of technical services at the school.
“If I don’t have to run both [electrical wiring] and network cabling, it enhances my capability to bring [wireless LAN access points] online, because I don’t need an electrician to come out and give me a circuit each time,” Ficklin says.
Standard 110-volt AC outlets, installed in the past for powering computer equipment, would be overkill for the 48-volt wireless LAN endpoints or phones, he adds.
The university has 100 Cisco Aironet wireless LAN access points on its 50acre campus powered by Catalyst 4000 switches with in-line power, Ficklin says. The switches also power 2,000 Cisco IP phones used in dormitories and faculty and staff offices.
PowerDsine Ltd. makes PSE patch panel equipment based on the draft specifications of the 803.3af standard. The company resells its products to other switch makers, particularly those with IP or LAN telephony products – Alcatel SA, Avaya, 3Com Corp. and Nortel Networks Corp. among them.
PowerDsine offers stand-alone midspan PSE patch panel products that can sit in front of an Ethernet switch and provide power over spare twisted pairs in Cat 5, 5e and 6 cabling. PowerDsine also makes endpoint PSE components for switches that can provide in-line power and data – endpoint PSE – over the same pairs, according to Amir Lehr, vice president of marketing for PowerDsine.
Endpoint PSE, Lehr says, is particularly useful for connections where all wires are used for data transmission, such as 10 bit/sec signals on four-wire Category 3 cabling, and Gigabit Ethernet on eight-wire Cat 5, 5e or 6 cabling – both of which have no “spare” wire pairs for transmitting power.
Cisco introduced PSE switch technology as part of its Architecture for Voice Video and Integrated Data product line in March 2000, mainly to provide in-line power to its IP telephones. Cisco says it has shipped 8 million PSE modules for its Catalyst 6000 and 4000 chassis lines, and its stackable 3550 switch.
Cisco’s PSE gear is based on the 802.3af standard, but it is only compatible with Cisco powered devices. Chris Cullin, manager of enterprise voice and video product marketing for Cisco, says the 803.3af standard will be adopted when it is ratified, which is expected next April.
Cullin says Cisco offers midspan and endpoint PSE gear. A midspan PSE patch panel product can power endpoints attached to older Cisco switches and routers – such as the Catalyst 5000 or routers that do not support in-line power modules.
But Cullin says endpoint PSE gear – such as the Catalyst switches – is safer to deploy, especially in buildings with older cable plants. While a cable might look like it has eight wires, “sometimes only four are actually punched down,” he says.
If running midspan PSE over older wiring, he recommends checking all patch connections to ensure the spare pairs of wires are connected. Endpoint PSE in-line power ensures the power will get there, “because you know right away if a connection can receive data or not,” he says.
