A clash of competing protocols will hold back Voice over IP deployments, according to a report from industry watcher Analysys.

The report said that one of the biggest obstacles to enterprise takeup of VoIP would be the existence of three separate protocols that manage IP voice calls.

Report author Margaret Hopkins said the session initiation protocol (SIP) was the most appropriate to manage multimedia calls over IP, although H.323 and the media gateway control protocol (MGCP) can also be used.

"I would debate whether to wait until full SIP-based PBXs are available before deploying VoIP," said Hopkins.

She warned that without SIP down to the handset or desktop, users would not get extended functionality. "They'll miss out on some interesting features," she said. "SIP is the most exciting protocol for VoIP. It has the particular advantage that you can add other data types in the packet stream, which makes it good for developers producing niche applications. To do that with H323 you'd have to request a change in the protocol standard."

Tim Stone, marketing manager for Cisco's AVVID products, said it was possible to mix and match. "Our IP phones support protocols including H323, Skinny Station Protocol and SIP," he said.

"Cisco gateways are controlled by MGCP. It is possible today to build networks which utilise all these protocols, and we do not see this as a barrier to VoIP uptake."

But Hopkins argued that a pure SIP approach would deliver the long-term benefits of VoIP. "It is true that you can use all the protocols together, but I can see this increasing costs and application development time, and it adds to uncertainty in users' minds."

Savings on voice calls will be a primary driver for VoIP uptake, the report said, although vendors have begun to sing a different tune and now stress the efficiencies and productivity boosts of IP.

"There are areas where enterprises can make immediate savings," said Hopkins. "Overseas offices that are off the main comms routes, such as Singapore, can connect to small branch offices where it's too expensive to justify a PBX."

This gives network managers another lever to pull directors into deployment. IP telephony brings branches much closer to the business. Call routing can make a remote receptionist part of a call centre, or maintain a 24-hour contact facility by shifting responsibility through time zones.

But to get the full benefit, organisations will have to reorganise the way they work. Steve Blood, research director at Gartner, said most had not yet begun to think about it. He added that this, rather than a protocol mismatch, would be the biggest obstacle to full VoIP implementations.

"For some enterprises with disparate PBXs, the ability to share a simple set of features across the network is light years ahead of where they are today," said Blood.

The VoIP debate has started in earnest in many corporate boardrooms, but - according to Hopkins - medium-sized enterprises which stand to benefit most are not getting the message.

She said the spread of broadband access technologies would be crucial if such organisations are to be persuaded they can deploy corporate-class communications. "It will depend on how easy it becomes to get DSL into branch offices. You can now get DSL kit that does MPLS, so you can prioritise voice on DSL connections, although SDSL is much better for supporting voice."

Although some telcos are trialing SIP, widespread deployment is not expected for up to two years.

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