The debate has gone on for years in slide-show sparring duels, but it escalated into a real-world street fight when IP PBX sales started to increase this year. LAN telephony sales increased from $2.9 million to $40.7 million between the second quarters of 1999 and 2000, according to market research firm Synergy Research Group.

Cisco shipped its Architecture for Voice and Integrated Data (AVVID) platform – the first enterprise-class IP PBX – in mid-1999, and 3Com has seen continued success selling its NBX line into small and midsize business sites.

"We started hearing more from the established PBX vendors in the third quarter of 2000, when the threats from these nontraditional players began to get real," says Jeremy Duke, Synergy’s president. "This is a disruptive technology, and a big part of the PBX business has been flat or even declining."

The gateway approach to LAN-side voice over IP is more cautious and incremental, preserving investments in traditional PBX platforms and leveraging their vaunted stability and "five-nines" reliability. The PBX continues to handle call processing, while the line-provisioning functionality is off-loaded to the IP network.

A gateway board in your PBX packetizes and compresses voice for transmission over IP and functions as a proxy server and virtual line card for IP phones that are plugged into Ethernet jacks. A gateway card with 24 ports can support up to 96 of these phones, so you can squeeze more capacity out of a PBX by supporting new users through voice over IP.

In contrast, IP PBX systems replace the center-stage switch fabric in the traditional PBX hardware with the IP network and move the call processing to an open server – typically Windows NT. The call processing and PBX functions such as call switching, trunking and station access can be distributed across different platforms or even outsourced. Of course, this flexibility means increased complexity and integration overhead.

The PBX faction questions the reliability of the data infrastructure but acknowledges that properly configured Ethernet networks with state-of-the-art switches are approaching the same 99.999% uptime that voice networks have achieved. The weakness is the NT server, which tends to destabilize and requires regular rebooting. Traditional PBXs are comparatively closed, but will run indefinitely without rebooting and can be patched without disrupting operations.

Gateways enable telecommuters

Symantec is an evolutionist that has embraced the gateway approach to convergence, although the initial focus is on remote desktops. Located in the middle of Silicon Valley, where rush-hour traffic congestion is rising almost as fast as housing prices, the software developer needed a way to provide full PBX features over DSL lines to its growing population of home workers.

Because it had a fairly homogeneous voice network with more than 40 Nortel PBXs worldwide, Symantec decided to alpha-test a Nortel line-side gateway card to deliver voice over IP to telecommuters. A small hub is placed in each home, and users plug their computers and phones into it. Voice and data can be delivered simultaneously over the same DSL connection, so no second line has to be installed for data.

The employee has the same phone number at the office and at home, and the phones ring in both places when calls come into the enterprise PBX. The local and remote IP phones support the same functions, including call transferring, conference calling and message-waiting lights. The gateways provide four times the port density of a traditional PBX line card, so Symantec is using them for expansion on campus.

"There is a big cost savings when you don’t have to buy another shelf in the PBX," says Neil Kole, director of communications and engineering at Symantec. There are also administrative savings because it’s easy to install and move phones.

"You just plug them in the jack," he says. "With traditional phones, someone with the proper skills has to move a cable pair or do some programming on the PBX."

Kole says the latest upgrade removed the last perceptible imperfections in the voice quality of the IP phones, and he now has no reservations about rolling them out anywhere.

IP PBXs are another story, however.

"We played with an IP PBX, but we were concerned about the reliability issues. Even if I had a green-field opportunity in a new branch office, I would put in a PBX with a gateway card to deliver [voice over IP] to the desktop," he says.

Fomenting a revolution down under

In Wellington, New Zealand, Neil Miranda, IS coordinator for the Ministry of Social Policy, can’t understand this halfway approach. The agency recently replaced a nationwide network of 160 Nortel PBXs with voice-over-IP technology based on Cisco’s AVVID platform. The infrastructure supports about 8,000 IP phones in more than 200 government offices and handles more than 150,000 voice calls each day. Except for Cisco’s internal network, it is the largest deployment of AVVID soft PBXs in the world.

"Telephony is becoming a system," Miranda says. "You don’t half roll out a new [human resources] or financial system, and it doesn’t make sense to do so with a telephony system."

Miranda settled on convergence when the government decided to expand the agency from 6,000 to 8,000 employees but wouldn’t budget additional funds for network operations. Combining voice and data into one infrastructure seemed the only way to achieve the necessary cost reductions.

The implementation took less than a month and required no end-user training. The network has been up and running for three months, and Miranda says his staff is fielding fewer complaints than it did when the old PBXs were in use.

"In addition to the efficiencies of having a single network, we also get so much new capability. The ‘power of one’ is starting to come together. I spoke at a recent [chief information officer] conference and told IT executives they need to embrace this technology now," he says.

Wireless LANs are ripe for convergence

But gateways still might be more practical in some specialized areas. Symbol Technologies in Holtzville, N.Y., has carved a nice niche delivering wireless converged voice and data to sites with mobility requirements, such as retail stores and hospitals. Wireless infrastructures are a lot more expensive than their wired counterparts, so users often have more upfront incentive to converge them.

Base stations mounted on the walls in a building create microcells with which wireless phones, PDAs and laptops communicate. Retailers such as Rite-Aid, Sears and May Co., find the setup ideal for taking inventory and keeping in touch with personnel roaming the sales floors. Hospital staffs use wireless devices to enter patient data or access information from anywhere.

Symbol provides its own handheld devices, which incorporate technology licensed from Palm and function as a phone, walkie-talkie and pager. At San Jose International Airport, American Airlines is trying them out for express check-in operations. Symbol works with voice gateway vendors to link its wireless voice/data LAN to a standard PBX.

The voice decision doesn’t have to be an either/or one. While the official rhetoric is quite polarized, both camps are actually hedging their bets. Cisco champions the IP PBX concept but is also a leading provider of voice gateways. Nortel is developing its own IP PBX line.

Meanwhile, peaceful coexistence may be the way to go. If you have a huge campus that has maxed out the capacity on an existing PBX, you can expand via an IP PBX and use the old and new platforms together.

Breidenbach is a freelance technology journalist and consultant.