Cisco Systems' IP-based PBX system was the only major system still not supporting a standard protocol that would cut the cost of voice over IP and pave the way for a new generation of VoIP applications. That all changes this week, as mounting customer pressure and the standard's potential finally convinced Cisco to get behind the Session Initiation Protocol.

The network-equipment vendor has planned a set of announcements that have the Session Initiation Protocol at their core. In addition to a SIP-compliant CallManager 5.0, they include SIP capabilities for Cisco IP phones, presence-awareness software, and multimedia communications software.

The messaging protocol delegates how VoIP phones establish contact and use call waiting, among other things. It will let customers mix and match VoIP products from different vendors. Support in CallManager 5.0 should make it possible for a customer to choose a cheaper SIP-based alternative to Cisco's VoIP phones, which can cost upward of $500 apiece. Cisco plans to support Research In Motion's BlackBerry and forthcoming Nokia dual-mode phones with Call Manager 5.0, though just about any standard SIP-based phone from two dozen or so vendors should work with the IP PBX.

Best Possible Fit

Support from the world's largest network equipment vendor is a significant shot in the arm for SIP. Cisco's decision is applauded by Ruth Harenchar, CIO of legal staffing firm Hobart West Group, which runs its telecommunications system on Cisco's VoIP products. "With interoperability, it gives you the opportunity to look at the best possible fit, whether it's for cost or for something else," she says.

Besides lowering the cost of VoIP via interoperability of systems, SIP has the potential to play a role in multimedia communications analogous to what HTTP has done for communications across the Web. It opens up the potential for video, data, and presence-awareness apps to be more easily used and shared among SIP-based devices and software. SIP is the underlying protocol used by Cisco's new Unified Personal Communicator, coming out this week, which lets a desktop user change from a VoIP telephone conversation with someone to a Web conference that incorporates video or desktop sharing with the click of a mouse.

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The value of the protocol is moving beyond VoIP, says Joe Burton, director of engineering for Cisco's unified communications business unit. "I think of SIP as a rich-media protocol," he says. "It's the unification of voice, video, instant messaging, presence and other data."

Cisco isn't the only one expected to tout SIP this week. Avaya, which embraced the standard in 2004, will reveal a modular messaging platform that uses SIP to integrate with Microsoft Exchange and IBM Lotus Notes, a Converged Communications Server that can support more SIP phones than it currently does, improved SIP-based presence-awareness server software, and a new version of its Communication Manager IP PBX that includes SIP functionality at no extra cost.

SIP is still maturing, even in the eyes of its biggest advocates. SIP products vary a great deal in functionality, and the world still is waiting for that promised plethora of interoperable third-party applications based on SIP.

And many businesses may not be ready for or even interested in SIP's flashier capabilities. "Have I looked at it seriously? The answer is absolutely not," says Hobart West's Harenchar, who's done only cursory reading on the protocol. The company just recently went all-VoIP. "We've introduced so much change," she says. "I'm looking at stabilizing and getting a return on the investment here before I do anything else."