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Feature Article
September 2003

Power Over Ethernet: What It Means For VoIP


The enterprise IP telephony hype has quieted down during recent times, and now, silently, implementations have begun. One indication that enterprise deployments of IP telephony systems are gaining momentum is the fact that all manufacturers have stopped investing in PBXs and have devoted development resources to IP technologies. However, when end users begin installing their shiny new IP phones, they�ll likely scratch their heads looking for that extra AC outlet to connect each phone, not to mention a cost-effective solution to cope with occasional AC power outages. Here�s where a new technology called Power over Ethernet (PoE), also known as Power over LAN, comes in handy.

Running power and data communication on the same cabling plant is an almost trivial concept, one that has been taken for granted for the last 126 years in analog telephony. But it is new to the LAN. Before PoE technology, IP telephones required two connections: one to the enterprise LAN and another to the electrical AC network. But now, enterprises using PoE can create an integrated data, voice, and powered network. The idea is simple, but its implications are enormous: Using the standard Ethernet network infrastructure and cabling, electrical power is added and distributed to drive connected IP telephones, wireless LAN access points, network cameras, and can even be used to extend battery life on a notebook computer.

With PoE, IP telephony becomes more reliable and cheaper to install, enabling enterprise companies to save thousands of dollars on their communications infrastructure. Outside of the office, PoE can be used in smart homes, integrated in Internet access on airplanes, trains and in public areas like airports, theatres, and conference halls, offering a universal power standard for traveling users.

Initially, Voice over IP (VoIP) systems suffered in terms of quality when compared with traditional telephony systems and the fledgling industry had to rapidly adopt a series of technical developments to reach today�s high-quality voice communication standard. Not surprisingly, enterprise companies were very reluctant to abandon their traditional PSTN systems, after all, they worked well and reliably, and represented a significant capital investment.

One of the crucial issues that slowed the adoption of VoIP systems is the issue of reliability. Companies witnessed the dramatic impact on productivity of the network server being unavailable to the workforce, and the prospect of the telephone system being down with the same regularity was enough to dissuade many companies from making the move. By supplying power over the same cable as the data network, these systems can now deliver the kind of reliability expected from a business-class phone system.

PoE technology saves the time and cost of installing separate power cabling, AC outlets, and wall warts. It further eliminates the need for a dedicated Uninterrupted Power Supply (UPS) for individual devices connected to the Ethernet. So, in a VoIP installation it is possible to centrally back-up IP telephones in the event of a power failure.

Everyone has high expectations of voice service availability. A common goal is to consistently achieve 99.999 percent availability with 5.3 minutes of downtime per year or less. By connecting a UPS to a PoE mid-span in the communications room, the entire IP telephony network becomes more reliable and ensures continuous operation during a power outage.

The key issue of implementation relates to handsets, which have long been a problem with VoIP. While they generally offer more functionality than a standard handset they also require power, unlike traditional phones that draw power from the connection. This can make it difficult to install some phones. PoE eliminates this problem because 802.3af-compliant telephones can be installed without requiring an additional power cable. VoIP phone vendors also benefit from a worldwide standard in cabling -- RJ45, so they do not need to make different plugs in order to sell their products in different countries.

PoE offers a simple means for the installation of IP phone handsets by eliminating the need for a separate Ethernet link and dedicated AC power outlet. The IP phone is plugged into the Ethernet switch and the midspan from which it gets data and power and the PC is connected to an Ethernet port on the phone. The expectation is that simplifying the installation of VoIP will accelerate adoption of both PoE and VoIP given the rapid and easily calculated ROI of the technologies.

IEEE 802.3af
At the urging of several vendors in mid 1999, the Institute of Electrical and Electronics Engineers (IEEE) formed a taskforce to standardize an approach for passing power over Ethernet, the most widely implemented data networking specification. The taskforce, called 802.3af, is run under the auspices of the 802.3 workgroup, the same group that developed the original Ethernet specification. While I was writing this article, Draft 4.3 of the standard was approved by the IEEE Standards Board on June 12, 2003, and was to be published on or before July 11, 2003, as �802.3af-2003.� The new standard also specifies the way to build Ethernet power sourcing equipment (PSE) and powered terminals.

So compelling are the benefits of PoE technology that many leading vendors have already incorporated it into their next generation IP devices. IP telephones made by Siemens, 3Com, Nortel Networks, Avaya, Cisco, Alcatel, Mitel, and others are already Power over Ethernet enabled.

The 802.3af standard defines two alternatives for PoE -- endspan and midspan. Endspan refers to an Ethernet switch with embedded PoE technology. A midspan resembles a patch-panel device, with multiple channels (typically six to 24), that is placed between any standard switch and the powered terminal. Each of the midspan channels has data input and a data+power RJ-45 output connector. Midspans are the ideal solution for upgrading a network without replacing switches and for low PoE port density. Many vendors offer PoE midspans today. Of course, another way to power an IP phone is through the traditional method where power is supplied via an AC adapter.

In the market, different PoE products exist, however not all are compatible with the PoE standard 802.3af. Like all global standards, it is important to maintain an open environment to enable interoperability between different terminal vendors.

In environments where an existing Ethernet switch has been installed and is providing VoIP Quality of Service capabilities, there is no need to purchase and install a new Ethernet switch to provide PoE functionality. In this case, the simplest means to power the IP phones over the LAN infrastructure is to add a dedicated external PoE mid-span. The advantages include savings in installation costs and preservation of existing infrastructure while supporting pre-standard as well as IEEE 802.3af standard terminals.

It will be interesting to observe the rate of adoption of VoIP technology now that this fundamental barrier to implementation has been removed. In my humble opinion, PoE technology will accelerate greatly the adoption of IP telephony among enterprise organizations looking to reap the benefit of a significant and immediate cost savings by coupling PoE and VoIP.

Amir Lehr is vice president of business development and strategic planning at PowerDsine, a leading player in Power over LAN technology providing the ability to deliver both power and data over a single network cable. PowerDsine offers converged power and data solutions to corporate users via it own range of equipment and via OEM agreements with the leading communications equipment manufacturers in the telecom and datacom industries. PowerDsine is a founding member of the IEEE 802.3af Task Force.

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