Sizing up VoIP servers

See correction at end of review

Voice over IP has reached the point where it's good enough to be taken seriously in the enterprise. The poor voice quality and dropped calls are things of the past, and the current technology delivers features and voice quality as good as, if not better, than what's available with POTS (plain old telephone service) or enterprise digital phone services. In addition, today's IP-based PBXes are reasonably priced, efficient, and flexible. But that doesn't mean they're all alike.

One of the things that struck us as we began testing these products is just how different they are. Two products, from Siemens and Avaya, stem from manufacturers with deep roots in legacy telephone systems. Another, from 3Com, clearly originates from the world of networking and the fourth, from Zultys, began as an IP telephone solution.

Also, while all four of these products are aimed at the enterprise, they target different segments. The 3Com and Zultys products are designed for smaller enterprises, while the gear from Avaya and Siemens are built to handle nearly anything, no matter how big.

What is common among all of these products is that they work on a standard Ethernet network, using standard infrastructure and cabling, but there are some special requirements. Network infrastructure hardware must be VoIP aware so that signaling protocols such as H.323 and SIP can make their way across the network, for example. Likewise, firewalls and other security products must be VoIP aware or calls won't get through.

Further, IP PBX vendors typically advise against deploying their products on your production data network. While it is possible to run your phone and data traffic on the same LAN, it can be very complex to manage the prioritization required to keep voice quality acceptable. Most manufacturers suggest a dedicated network.

We tested the 3Com, Avaya, Siemens, and Zultys IP PBXes at the Advanced Network Computing Laboratory at the University of Hawaii (for details on test procedures, see "How We Tested"). We created a dedicated network of VoIP-aware switches and infrastructure with ties to the public telephone network and the Internet. We conducted performance testing where possible with Spirent Communications' Abacus 5000, and we tested usability and features by making a lot of phone calls to see how they worked.

What we found is that these products are feature-rich. Each provides all the familiar telephony functions, from putting people on hold with insipid music, to transferring calls and recording voice mail. But each has capabilities that go far beyond the basics.

Even better, these PBXes can send phone settings out to the telephone sets attached to the network, providing great control over how the phones work, which features are available to which users, what locations the phones can call, and how the phones can be used. In each case, settings can be changed on the fly.

In most cases, the vendor's IP phones attach to the PBX from outside the network as well as inside. This means that you could take your phone on the road with you, if you were so inclined, and use it from the high-speed Internet connection in your hotel room. While toting a desk phone might not be very practical, software phones, or “softphones,” available for these products accomplish the same thing, as long as you don't mind using your computer to make phone calls while you look at an onscreen picture of a real phone.