John Ridley is stuck between the old world of circuit-switched telephony and the new world of voice over IP.

How soon the Coca-Cola network executive can move forward depends largely on which IP telephony standards key vendors support and how true they stay to those standards.

Ridley, who is looking to replace a loosely connected collection of old PBXs, is among a growing legion of network executives who say products based on Session Initiation Protocol (SIP) are the best bet for delivering the true benefits of VoIP. Such gear could help simplify network management and support new applications, they say, although only if the products boast Ethernet-like interoperability.

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"The problem with IP telephony equipment today is that there is no [interoperability] among vendors," says Ridley, whose converged network would serve 70,000 employees.

Network executives are wary that vendors will repeat the mistakes they made with the older, less-functional H.323 technology. While H.323 has been implemented widely, vendors took so many liberties with it that getting their products to work together can been difficult.

"There are a lot of slacker customers out there like us who are just sitting on our old legacy stuff, waiting for the market to evolve," Ridley says.

Making the case for SIP

Work on SIP, now an IETF standard, started in 1995. It was designed to run on IP and supports a plethora of communications technologies from voice to instant messaging to video. SIP also lets users establish presence at different locations on a network, saying "I am here" and letting everyone or just a select group know it. SIP promises to support new services such as click-to-dial phone calling, interactive voice response navigation of Web sites and conferences that are set up when all participants are ready.

SIP is considered more efficient than H.323, which is commonly criticized as being too chatty, sending lots of messages over the network and creating potential congestion if VoIP is heavily used. Critics of H.323 say the overarching standard for interaction among a set of other standards is too unwieldy to customize.