XO Communications' Blog

SIP Interoperability - Are We There Yet?

[ 2 ] May 15, 2012 | By

Let’s try to find an answer to this question.  Many businesses are either in the planning or implementation phase of their SIP trunking deployment. One of the key objectives for them is to have an optimal and stress-free SIP trunking deployment.

To achieve that, businesses can do a ‘Pilot Trial’ to test how their current SIP- enabled infrastructure will interoperate with the SIP service provider. One of the most important things to define before starting a trial is the success criteria and the duration. Otherwise, a trial might become an endless project, consuming more time and financial resources. A prolonged interop test trial will cause overall SIP trunking deployment delays and will minimize the benefits of implementing SIP trunking. But it’s still a very critical step of the deployment and any industry expert will advise against skipping or hastening it.

As we all know, SIP is an ever changing and evolving VoIP communication protocol. SIP is maturing but it’s still not “plug and play” ready. There are RFCs published by IETF (Internet Engineering Task Force) that do a great job of specifying SIP standards and help streamline basic SIP implementations, but still there are some specific areas and features where implementation is left to vendor’s own interpretation.

Many times various vendors’ interpretations don’t match and they each implement the same SIP features in different ways. That’s a perfect recipe for an interop nightmare! But there are significant efforts being made to mitigate interop issues by having RFC/IETF drafts to address specific areas that may not be covered in main RFCs.

Other groups at the forefront of addressing interop issues include VoIP equipment vendors and leading SIP trunking providers who perform interop testing with their equipment and SIP services, and ‘certify’ a specific solution and the equipment needed.  This gives customers a great deal of confidence when planning and evaluating various vendors and SIP trunk providers.

The following are key factors for a good SIP interop certification process:

  • Software Version of IP-PBX Tested and Certified
    • Every now and then an IP-PBX vendor comes up with a major software release which includes new features and enhancements.  A good SIP trunking provider refreshes their certification after testing with every such major release.
  • Test Plan
    • Test plan serves as a success criteria of a pilot trial. A comprehensive test plan is very critical. It should not only cover basic call scenarios but also various feature related call scenarios. With SIP there’s always more than one way to implement or use features.
  • Configuration Guide/Application Note
    • The outcome of interop testing should not only be a confirmation of proper working between the IP-PBX or SBC with the SIP trunking provider but also good documentation of test results. Such documentation should include all issues and limitations discovered during testing and should list any possible workarounds or solutions found for such issues and limitations. Documentation should also contain configurations (screen captures or CLI config) of the IP-PBX or SBC used during testing. That way the document serves as a best practice for customers.

This certification process should help customers in their planning, evaluation and implementation phase. Still, every SIP trunking deployment is unique and will require some form of testing by the customer. But these efforts should help them to minimize their test trial period.

So the answer to the question is we may not have reached a point where SIP trunk implementation is a breeze, a “plug and play” solution, but leading equipment vendors and SIP trunking providers are taking all necessary and prudent steps so that customers don’t have to worry about SIP interoperability challenges during their SIP trunk deployment.

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Category : Communications, SIP Trunking

About Himanshu Kapadia: I'm a Data Engineer for XO Communications. My role includes performing interop tests with XO SIP services. I have over 5 years of experience in the Voice over IP (VoIP) field. I hold a Master's degree in Electrical engineering with Telecom specialization from Southern Methodist University (SMU) at Dallas. I also hold a bachelor's degree in Electronics engineering from South Gujarat University, India. My hobbies include astronomy and photography. View author profile.

Comments (2)

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  1. David S. Emel says:

    Seems like an enormous expense for something that needs the TCP/IP stack rewritten… SCTP… maybe??

  2. Himanshu Kapadia says:

    SIP is an application layer protocol designed to be independent of transport layer protocol. Interop challenges with SIP are common on all type of transport layer protocols. There are some initiatives to run SIP over SCTP but it seems to be in its early phase.

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