Making convergence a real live wire

New technology that uses network wires to power IP phones could aid IP telephony deployment, according to industry insiders.

Known as “Power over Ethernet” (PoE), the technology sends electricity over network conduits to IP phones. It cuts down on the number of wires required to support the phones (normally you’d need two: one for power and one for network connectivity), thereby simplifying cable management.

As well, PoE facilitates “converged” network buildouts, wherein the network carries both data and voice. Convergence is supposed to make networks simpler to manage. PoE enhances that, said Trent Ready, business development manager, voice with 3Com Canada in Mississauga, Ont.

“With convergence…the implied promise was convenience, lower cost of ownership, easier management and greater flexibility. With Power over Ethernet, now we’re starting to see that promise being delivered. You can deploy any Ethernet product wherever you have a Cat 5 jack and not have to be concerned with whether there’s a wall outlet (for electricity) there as well.”

PoE infrastructure comprises PoE switches and IP phones. The phones connect to the switch via Cat 5 cables, which serve the phones with electricity and network connectivity.

Behind the switch, an uninterruptible power supply (UPS) provides peace of mind. Should the power go off, the UPS supplies a direct current to IP phones, such that the phones work even if the lights don’t.

Ready said this power-safe infrastructure addresses a frequent concern about IP telephony. Normally, IP phones rely on common electrical wall sockets for power. If the power goes off, so does the phone. A UPS ensures that users always get a dial tone.

3Com is one of the first network gear makers to offer standard-compliant PoE equipment. The SuperStack 3 Switch 4400 PWR (a 24-port 10/100 switch) is the main building block in 3Com’s solution, which includes PoE-ready IP phones and a wall-mounted jack (the “Network Jack”) that allows a single cable to support both PoE and non-PoE devices.

Like Foundry Networks Inc., another PoE player, 3Com based its gear on the IEEE’s PoE specification, 802.3af – “a fairly complicated little standard,” according to Geoff Thompson, vice-chair of IEEE 802, a communications standards group.

“There are a lot of technical issues,” he said. “One of the big issues is circuitry that does not leave standing power on the outlet.”

Standing power means electrical sockets are always live. PoE developers must ensure that connector circuitry effectively overcomes this phenomenon, so users can plug non-PoE equipment like computers into PoE ports and rest assured the port will not electrocute the PC.

Thompson said IEEE 802 kept this problem in mind when developing 802.3af.

“We have a very low power pulse that probes the outlet when there’s nothing connected. When you plug something in, it looks for a particular signature that we hope is unique to Power over Ethernet devices. If the outlet sees this signature, it turns the power on.”

Today 802.3af is a draft specification. Thompson said the IEEE expects to ratify the standard by June. In the meantime, 802.3af could change as vendors haggle over the details. How can customers be sure that 3Com’s current, pre-ratification PoE offering will work with post-ratification equipment?

“That’s always a challenge,” Thompson said, explaining that vendors make a “judgment call” as to when they think the standard is sufficiently stable to adopt.

3Com is confident that 802.3af will not change much before ratification. The firm was instrumental in creating the spec and has a good handle on its progress, Ready said.

Ted Malos, director of technology with Ventura Unified School District (VUSD) in Ventura, Calif., said he is “somewhat” worried that 3Com’s pre-ratification PoE equipment will not work with post-ratification gear. Nonetheless, VUSD is an early adopter of the 4400 PWR platform, and the district enjoys the benefits of the buy.

PoE makes network architecture simpler and less expensive to do, Malos said. For instance, employing the Network Jack means VUSD can mix and match ports according to a teacher’s needs. It’s an inexpensive addition to the network compared to the change order required when teachers request that ports be relocated.

“A change order…cost would be somewhere between (US)$500 and $1,000….The cost of the Network Jack is $140. It’s much easier to swallow.”

Although happy with the 3Com PoE platform, Malos urged the vendor to maintain its focus on standardization, for the good of customers. “That’s a step toward interoperability. We need that. Then the prices will really come down.”

3Com’s 4400 PWR is priced at $3,745. For more information, see For info about Foundry’s PoE platform, visit

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