SIP trunking challenges

There are real challenges of interoperation among multivendor gear. This is part of the reason why SIP Trunking hasn’t been more widely adopted.

The interoperation issue is different from an interoperability issue. Interoperation is what enterprises have to deal with because there is no true interoperability, i.e., a universally accepted and complied-with standard allowing for plug-and-play connection among multiple vendors’ products. In the absence of this interoperability, enterprises must deal with one-off interoperation--making the different piece-parts of their own system work together to pass SIP traffic.

Interoperation needs to be done on two planes, signaling and media. Signaling is where the strict SIP translations have to be done; on the media plane, the challenge is translating different products’ handling of media inputs like DTMF, so that DTMF tones generated by an endpoint on one vendor’s system actually get passed and re-created correctly at the other end, where the recipient may be on a different vendor’s system.

Another media-translation issue arises when different codecs are used, and the SBC must perform transcoding so that the endpoints can exchange media. DTMF issues, of course, can be a major stumbling block in an enterprise that uses IVR to interact with customers.

The key is going into your SIP trunking implementation with a clear idea of exactly the scope of the challenge you are faced with when it comes to interoperation. Think of it as a matrix of interconnections that can grow unwieldy if you’re trying to put together too many one-off interoperations. You need a really solid implementation plan.

Why isn't SIP Trunking being more widely adopted? About 80%-90% of enterprises have implemented some SIP trunking, yet less than 10% had fully rolled out the service. Most experts ascribe it to the very deliberate pace of the overall VOIP migration; IP-PBX rollouts have been slow, especially as the recession delayed upgrade cycles, so this affected the practical ability to roll out SIP trunks.

Also, there’s a lot of complexity in bringing all this together. It’s just going to take time. Most enterprises’ carrier contracts expire at a staggered rate means you can’t just forklift out the old circuits without incurring prohibitively large termination penalties.

In a historical context, the SIP trunking migration hasn’t been that slow when you compare it to, for example, the migration away from TDM.

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