How Voice Application Developers can Surmount Interoperability Problems

IP media server platforms have helped bring about the shift to IP infrastructure in the enterprise. IP media servers are a key component for delivering such pervasive applications as unified messaging, IVR, speech servers, contact centers and more. Such servers use SIP instead of TDM interfaces to connect these typically adjunct applications to the core real-time call control and switching system in the enterprise — the PBX.

But there are few perfect scenarios. As Jim Machi, VP of marketing for the Dialogic® Corporation, tells it, “Unfortunately, virtually all first-generation IP-PBXs relied on proprietary IP signaling stacks. Subsequently, as SIP was anointed as the signaling standard for VoIP, it has often been implemented by PBX manufacturers with proprietary extensions, or at best, disparate interpretations of RFC3261, particularly when functions beyond ‘connect and disconnect’ are required. Where does that leave voice applications developers seeking to deploy their applications on an IP media server platform? It leaves them suffering from IP, which in this case means ‘Interoperability Problems’.”

Machi’s point is well made as is evident by Microsoft’s (quote - news - alert) entry into the unified messaging space with Exchange Server 2007. Although Exchange Server 2007 utilizes SIP and RTP as the signaling and transport protocols, for all but one PBX integration Microsoft recommends IP media gateways such as those from Dialogic to translate SIP signaling into a language the PBX is sure to understand. The landscape for true SIP interoperability from the PBX manufacturers to IP media applications is one that is evolving, but to be sure, it doesn’t ‘just work’.

In order to make most applications interinteroperable with today’s crop of IP-PBX and hybrid IP-PBX systems on the market or being deployed, Machi says that developers must do system-by-system SIP interoperability testing, which ultimately leads to necessary changes to the SIP signaling implementation on one side of the equation or the other.

“If you’re Microsoft, making huge waves in the enterprise communications system space and partnering up with Nortel and others,” says Machi, “you may stand a pretty good chance of influencing changes on the IP-PBX side of the SIP stack to make your stuff work. And in fact Microsoft and Nortel just announced Exchange Unified Messaging and CS1000 SIP interoperability as the first deliverable of their agreement to collaborate on unified communications. But for most ISVs and voice application developers, the task is daunting and you’re not likely to get the big PBX players to make changes to accommodate your needs.”

So is Machi slamming SIP and the way that IP-PBX manufacturers implemented it? “Yes and no,” replies Machi. “The deeper issue in integrating voice applications to switching infrastructure is related to the supplementary services. And they’ve always been a bit of a gotcha. Whether it’s seemingly insignificant things like desktop message waiting indicator control for voice mail, or more important things like making transfers reliably and efficiently so you don’t drop customer service calls, integrating voice applications reliably to PBX infrastructure has always been a challenge for the independent development community.”

So what’s a developer to do? Should voice application developers wait for SIP standards to evolve more fully? Should they wait for some 3rd party to figure out how to interop via SIP to all the IP-PBXs on the market and license that knowledge or the related SIP stacks? Is there still value in deploying an enterprise application on an IP media platform near term, or is it better to wait until SIP implementations really become normalized across vendors? And will that ever happen?

One solution is offered via IP media gateways, as Microsoft discovered. As Machi says, “Migrating an application to a pure IP platform has many benefits beyond direct IP interoperability with an IP-PBX. And certainly over time there is the opportunity to work through the SIP implementations of the various IP-PBX manufacturers, and starting with the market share leaders is the obvious approach, as Microsoft exhibited by going direct with Cisco, and now moving on to co-operate with Nortel. In advance of that process, and to interface back to all the legacy switches, an IP media gateway is the solution, providing the translation to TDM interfaces required to make the solution fly.”

Unfortunately, most gateways have been designed for applications such as SIP trunking and other forms of toll bypass, so not all gateways have been designed or developed with a media application in mind — again, not readily capable of handling the supplementary features and functions that a messaging, IVR or contact center application needs.

“However, Dialogic® IP Media Gateways are actually designed expressly for this purpose, on both sides of the network,” says Machi. “Dialogic is the only enterprise gateway provider that cut its telephony teeth on adjunct voice applications and knows their needs and nuances inside out. So Dialogic started its gateway design process by borrowing technology from its market leading and unique PBX integration boards.”

Such boards emulate digital PBX station equipment with separate digital audio and data paths, and whose proprietary signaling had been decoded for the major PBX and hybrid key system manufacturers over many years — sort of like working through today’s SIP implementations. . .

“By interfacing to the PBX in this way,” says Machi, “a tight signaling and audio path is established enabling fast and reliable transfers and data signaling, just the kind of thing you need for messaging and IVR applications. Dialogic used this technology to develop a series of IP media gateways to enable these applications.”

“The Dialogic SIP implementation in the gateways takes the supplementary service information from the PBX port and translates it into a well documented SIP interface for the IP media application,” says Machi. “And Dialogic has carried that through to its digital T1/E1 series of gateways as well, starting with a strong implementation of Q.SIG and other line side digital ISDN and CAS protocols, all translated to SIP.”

“Most IP-PBX architectures on today’s market are hybrid TDM — IP,” says Machi, “so digital station ports and line side T1/E1 interfaces are still standard fare, even on newly deployed systems, providing the connectivity for Dialogic gateways to perform their translation magic. So while the landscape remains jagged with respect to SIP interoperability, especially for functions beyond basic make-call/disconnect-call functionality, Dialogic has delivered a transition solution for IP application providers enabling them to make the move with assurance.”

It’s like they are a little pill for IP, alleviating SIP interoperability problems.

Richard Grigonis is Executive Editor of TMC’s IP Communications Group.