Alan Percy
Alan Percy is Senior Director of Product Marketing at Dialogic, responsible for marketing of the the company's media server and...
Read Full Bio >>

Alan Percy | June 08, 2009 |


SIP Interoperability - Why Is It So Hard to Achieve?

SIP Interoperability - Why Is It So Hard to Achieve? The problem is that RFC 3261 that defines SIP has become "everything to everyone" and bloated in both size and in flexibility.

The problem is that RFC 3261 that defines SIP has become "everything to everyone" and bloated in both size and in flexibility.

For those of you that have deployed SIP-based solutions or SIP Trunking, there is a pretty good chance that you've had to navigate your way through the maze of SIP interoperability, wondering why it is so difficult to get a straight answer out of anyone on whether two systems will work together or not.SIP is supposed to be a standard and eliminate many of the challenges with integrating systems from various vendors together, right? If my IP-PBX is RFC 3261 compliant and my SIP Trunking service provider is RFC 3261 compliant, they should just work, correct? Well--maybe or maybe not. Most likely there will be interoperability issues.

Today I thought it would be good to start a multi-part series of posts to explore why SIP interoperability seems to be as challenging as it appears, how the vendors are dealing with it and solutions you can use to solve difficult interoperability challenges.

The Root Cause Let's start with a discussion on the root causes that make SIP interoperability difficult. The problem starts not with technology, but with the way that IETF Requests For Comments (RFCs) are developed. As opposed to the old ITU specifications that the Telecommunications Industry has lived with for the last four decades, IETF RFCs and Drafts are developed in an open and communal environment, using committees and consensus to craft the specification. This has very many positive benefits, but also a few predictable negative side effects. The problem is that RFC 3261 that defines SIP has become "everything to everyone" and bloated in both size and in flexibility.

Performing a simple word count on RFC 3261 yields some interesting insight into the problem: Weak Terms May = 381 Should = 344 Option = 144 Can = 475

Strong Terms Shall = 4 Must = 631

As you can see, the number of weak terms "May," "Should," "Option" and "Can" outnumber the stronger "Shall" and "Must," which results in a very loose specification that allows the developers of SIP-based systems to make plenty of decisions on features of functions. The byproduct of this is that two systems can be completely RFC 3261 compliant and completely incompatible.

Examples In our experience, there are no fewer than five "correct" ways to transport DTMF tones from one end point to another: * In-band--leaves the DTMF tones in the RTP streams * RFC 2833--uses specialized payload packets in the RTP stream to indicate a DTMF tone * SIP NOTIFY--uses a SIP message to indicate the presence of a DTMF key press * SIP INFO (Nortel)--a technique frequently used in Nortel systems that uses a SIP INFO message * SIP INFO (Cisco)--a variation on the above, but with some slight modifications.

Another example that is causing a lot of grief right now whether to transport the SIP messages over UDP or TCP. The RFC indicates that either is okay and recommends supporting both, but few manufacturers actually do support both. The vast majority of equipment and application developers chose SIP-over-UDP. Microsoft chose SIP-over-TCP. Again, both are within specification and completely incompatible.

While these technical challenges may seem difficult to overcome, they can be solved. However, the political issues are another story. I'll discuss these in the next post.The problem is that RFC 3261 that defines SIP has become "everything to everyone" and bloated in both size and in flexibility.


Enterprise Connect Orlando 2017
March 27-30 | Orlando, FL
Connect with the Entire Enterprise Communications & Collaboration Ecosystem

Stay Up-to-Date: Hear industry visionaries in Keynotes and General Sessions delivering the latest insight on UC, mobility, collaboration and cloud

Grow Your Network: Connect with the largest gathering of enterprise IT and business leaders and influencers

Learn From Industry Leaders: Attend a full range of Conference Sessions, Free Programs and Special Events

Evaluate All Your Options: Engage with 190+ of the leading equipment, software and service providers

Have Fun! Mingle with sponsors, exhibitors, attendees, guest speakers and industry players during evening receptions

Special Offer - Save $200 Off Advance Rates

Register now with code NOJITTEREB to save $200 Off Advance Rates or get a FREE Expo Pass!

March 8, 2017

Enterprise IT's ability to innovate is critical to the success of the business -- 80% of CIOs agree. But the CIO role has never been more challenging than it is today, with rising operational respo

February 22, 2017

Sick of video call technology that make participants look like they're in the witness protection program? Turns out youre not alone. Poor-quality video solutions can give users an unprofessional ap

February 7, 2017

Securing voice communications used to be very simple since it was generally a closed system. However, with unified communications (UC) you no longer have the walled protection offered by a dedicate

February 24, 2017
UC analyst Blair Pleasant sorts through the myriad cloud architectural models underlying UCaaS and CCaaS offerings, and explains why knowing the differences matter.
February 17, 2017
From the most basics of basics to the hidden gotchas, UC consultant Melissa Swartz helps demystify the complex world of SIP trunking.
February 7, 2017
UC&C consultant Kevin Kieller, a partner at enableUC, shares pointers for making the right architectural choices for your Skype for Business deployment.
February 1, 2017
Elka Popova, a Frost & Sullivan program director, shares a status report on the UCaaS market today and offers her perspective on what large enterprises need before committing to UC in the cloud.
January 26, 2017
Andrew Davis, co-founder of Wainhouse Research and chair of the Video track at Enterprise Connect 2017, sorts through the myriad cloud video service options and shares how to tell if your choice is en....
January 23, 2017
Sheila McGee-Smith, Contact Center/Customer Experience track chair for Enterprise Connect 2017, tells us what we need to know about the role cloud software is playing in contact centers today.