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The lack of choices in phones should also concern anyone considering VoIP. Even though the vendors tout the new open paradigm on which IP telephony has been built, VoIP systems are still even more proprietary than legacy PBXes. With a legacy PBX, eGen or any company can give most of its employees inexpensive analog phones for less than $50 each, from any vendor. By comparison, the only IP phones available are equivalent to expensive digital phones, ranging from $300 to $600, and are not interchangeable from vendor to vendor. Such incompatibility will lock you in to one vendor for every single phone until standards, such as SIP (Session Initiation Protocol), Megaco or some version of H.323, provide more choices. (See "Making Sense of VoIP Standards".)

New Applications

Converged networking enables new applications, such as integrated messaging, which provides a way to view and listen to voicemail messages from an e-mail application. Receiving your e-mail and voicemail messages together, you can select which messages to listen to first. This feature can help a traveling employee who doesn't have to make two calls from his or her hotel to check voicemail and e-mail.

Nortel's CallPilot voicemail solution is compatible with the widest range of e-mail systems. Cisco's voicemail application supports only Microsoft Exchange. Therefore, to take advantage of integrated messaging, the IT manager must use both products. To avoid this problem, we suggest you test a best-of-breed approach, by combining Nortel's CallPilot with Cisco's VoIP phone system. You'll know how well this will work out, however, only if you try it for yourself.

In theory, once your phone runs on IP, it can follow you to any network that talks IP, along with all the features programmed into your phone. As such, VoIP could be a boon for telecommuters. But such transmissions must be done carefully, without opening your phone system to the Internet. To assure security, you'd need private circuits or a VPN; the cost of the latter would be extra latency, degrading the quality of the voice connection.

Our fictional company, eGen, does not have to worry about the power problems that involve most IP telephony solutions, as it uses its own products to back up the whole campus. Unless you also make your own generators, this will be an issue for you. A legacy PBX usually can provide power from a centralized location across the twisted-pair connections, but it's more difficult to do so on an Ethernet LAN. The phones will be on their own in a power outage. Fortunately, each of the vendors provided an option to distribute power to the phones--directly from the switching equipment or via an unused pair that could be tied into a panel providing power. And there's always the option of plugging the phones into outlets in the office. Meantime, the IEEE 802.3af committee is arguing about the best way to standardize power distribution.

Although our RFP asked for a pure-IP phone solution, Avaya and Alcatel made the valid point that their platforms would have the built-in capability to offer legacy phones as well. For some, this might be an attractive way to start before migrating to IP phones. Nortel did not mention its migration plans, but Cisco is clearly the only vendor that would not be able to offer anyone such a path.

EGen also is in pretty good shape from the data networking side, as it has a high-speed LAN already in place. If your company has a WAN with slower links, such a solution will be much more troublesome. All the vendors use the G.711 standard for the transport of the voice packets. G.711 essentially takes the standard 64 Kbps used in PCM (pulse-code modulation) and adds IP headers, bringing the bandwidth usage to about 80 Kbps of data. This would not add a significant amount of traffic on a switched gigabit or Fast Ethernet backbone.

What is more worrisome is that another application might stomp on a network's voice traffic. To prevent this problem, most of the vendors support 802.1p at Layer 2, as well as DiffServ (Differentiated Services) prioritizing schemes of IP packets, from the phone to the server. To save bandwidth, each vendor provides a silence-suppression feature, which means that no data is transmitted during pauses; that's hard for many users to get used to.

The vendors also provide the option of turning on compression using the G.729 standard, which cuts the bandwidth requirements down to about 8 Kbps. This feature is especially helpful for running voice-over-WAN connections, but we recommend testing the quality first.