Protocol standoff! Version 4 of the H.323 call control protocol for IP telephony is just about ready to hit the streets, but SIP has been stealing the spotlight as an IP-centric apps enabler. Many carriers want both - Online - Session Initiation Protocol

Telecom Asia, Jan, 2002 by John C. Tanner

All this, combined with the growing number of Web-application programmers, compared to telephony-application programmers, is fueling the rapid development of SIP domains and applications, Biller says.

The latest and greatest

The buzz about SIP, in fact, is loud enough that carriers are talking less about H.323 these days, and the arrival of new and improved H.323 Version 4 isn't doing much to change that.

"I have not heard a heightened demand from carriers for H.323 version 4 over the previous version," says Mindy Hiebert, a carrier convergence infrastructure analyst with Yankee Group, who goes on to say that, without exception, carriers are requiring vendors to provide SIP-capable platforms today.

"Carriers state that they will `tolerate' a migration to get to SIP, but the term is used very loosely," Hiebert says. "SIP is a critical requirement. Without it, softswitch and applications vendors will find significant obstacles with selling equipment to carriers today, or in the future."

Meanwhile, she adds: "In the conversations I have had with greenfield carriers, they are deploying SIP only with a `latest and greatest' attitude regarding what they plan to implement in their networks."

One probable factor in determining SIP's adoption rate will be its selling point of easy integration with other IP-based apps at a time when carriers are looking for new revenue-generating enhanced offerings to supplement their main money-making service: voice.

"To position themselves for long-term success, carriers must find ways to combine revenue-generating' voice services with the IP network's economies of scale and flexibility," says Siemens' Biller. "Certainly H.323-enabled VoIP service is a step in that direction. However, given that there no longer is a significant difference between the price of an IP telephony call and that of a traditional phone call, the initial attraction of VoIP is fading quickly. Service providers therefore recognize they must add value to basic IP telephony service if they are to create sustainable revenue streams, [and] that added value is found in SIP-enabled multimedia applications."

Yankee Group's Hiebert confirms that the market has "rallied around SIP as the enabler of packetized voice enhanced services -- even though these services are yet to be seen".

Getting cozy

However, none of this is to say that H.323 is on the way out as many SIP proponents claim, or at least hope. In fact, H.323's main advantage at the moment, Hiebert estimates, is that it's already here and in widespread use worldwide. "For the carriers using it already, H.323 is `good enough' for present network initiatives," Hiebert says.

What that means, essentially, is that there's more likely to be a long, cozy period of co-existence between H.323 and SIP in the market.

Biller takes this idea a step further: "To service providers and vendors looking beyond the IP telephony market, SIP and H.323 are not competing standards," he says. "Rather, they regard each as having a legitimate role to play in next-generation networks. Established and new providers alike are seeking IP networking solutions that support both SIP and H.323, especially incumbent operators who must be able to migrate their networks to all-IP infrastures while still protecting their investments in circuit-switched gear."