SIP interoperability and multimedia support: Has it come far enough?

VoIP, unified messaging, products and services

In part two of our discussion based on an interview with Greg Brashier, COO of Virtual PBX, today we'd like to share our opinions on the progress of session initiation protocol (SIP) interoperability. 

SIP is the predominant protocol used to control voice "sessions" for VoIP and it was also designed to provide multimedia session control. Introduced with great fanfare in 1996 by the Internet Engineering Task Force (IETF), multi-vendor support for SIP interoperability has seen some success for basic voice call features like call setup and tear-down. However, more advanced feature support for multimedia seems to have stalled. And the long-term vision by some foreseeing SIP as a possibility replacement for Signaling System 7 (SS7), the current PSTN call control protocol seems at best a very remote dream.

ANALYSIS: Advanced SIP interoperability is slow in the making

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In part two of our discussion based on an interview with Greg Brashier, COO of Virtual PBX, today we'd like to share our opinions on the progress of session initiation protocol (SIP) interoperability. 

SIP is the predominant protocol used to control voice "sessions" for VoIP and it was also designed to provide multimedia session control. Introduced with great fanfare in 1996 by the Internet Engineering Task Force (IETF), multi-vendor support for SIP interoperability has seen some success for basic voice call features like call setup and tear-down. However, more advanced feature support for multimedia seems to have stalled. And the long-term vision by some foreseeing SIP as a possibility replacement for Signaling System 7 (SS7), the current PSTN call control protocol seems at best a very remote dream.

ANALYSIS: Advanced SIP interoperability is slow in the making

For those like Virtual PBX that would like to see more feature support and faster carrier-to-carrier interoperability, we look back 20 years ago for some history lessons about interoperability. Today SS7 and CCSS7 (Common Channel SS7) are widely supported with direct carrier interconnections, largely negating the need for gateways to place a call over the PSTN. However, when SS7 was first introduced 30 years ago, each carrier supported its own SS7 network. It wasn't until government intervention requiring 800-number portability that individual carrier SS7 networks more became more fully integrated because they had to in order to support portability. Lesson 1: Sometimes it takes government intervention (in this case a court order) to enforce interoperability.

Also looking back three decades ago, we recall the lesson of the message waiting indicator, displaying on a desktop phone when a voice message was waiting. When the feature was first introduced, callers who were connected on different vendor PBX systems (or on different vendor's central office switches) could not get their indicator light to work. It wasn't until large customers complained loud and long to the vendors (with threats of returning both vendor systems) that the vendors were forced into making the lights work. Lesson 2: Customers can influence vendors it they complain loud and long.

Applying these lessons to our SIP interoperability issues today, neither the government (nor the courts) seem to have any compelling reason to enforce SIP interoperability. Customers seem largely unconcerned about SIP interoperability because the PSTN acts as a gateway "just in case" to make up for the lack of interoperability. Customer demand for multimedia SIP interoperability is also muted. So the bottom line is that vendors have few compelling business reasons to go beyond the interoperability progress they've already made for multi-vendor support.

If you agree -- or especially if you disagree with our logic, please feel free to send an e-mail to Larry by clicking on his contact information tied to this newsletter, and we will publish your thoughts. In the meantime, we'll go back to our regularly scheduled topics next time with announcement coming from Interop.

Read more about voip & convergence in Network World's VoIP & Convergence section.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Larry Hettick is a principal analyst at Current Analysis.