Manufacturers, service providers and enterprise customers are finding that SIP Trunking is not always an easy service to implement. SIP trunking is not easy to support if things go wrong.
In February 2011, The SIP School carried out a survey sponsored by Techistan that resulted in over 400 industry professionals responding (58% were in the U.S.). The survey's purpose was to look at SIP trunking and specifically, to find what the most common issues during SIP trunk deployment. To gain access to the full report, "The SIP Survey, 2011", register on the SIP School mailing list. The SIP School offers the online SIP training and certification. Techistan is an online news service and community of reporters and bloggers who collaborate in profiling and reviewing new technologies.
The survey posed 11 questions. This blog will focus on three of the questions. The first question is "If you've had problems, where have the issues been?”
The issues are divided into three categories; the SIP trunk provider; at the edge (NAT and SBC); and the PBX and its configuration. Although the PBX response was the highest, the majority of issues are caused by the provider and NAT/SBC edge devices. I wanted to focus on the first two issues and not on the PBX.
The second question is "If the problems were found to be on the SIP Trunking provider side, what were they?" 
This question offered nine possible responses. All of these problems have been issues since VoIP started to be supported. What is surprising is that they remain problems for the enterprise. You would think the providers would have learned how to avoid the nine problems. The basics of SIP and SIP trunking should not be new to the providers. These problems were expected a few years ago, but should not be surfacing now.
Looking at some of these problems:
* A codec mismatch is surely negligence or ignorance today. Could this be a situation where networking staff either does not know what is correct or the documentation is written poorly?
* Registration failures are usually account issues such as incorrectly entered passwords.
* One way/No audio issues are common problems that anyone deploying SIP Trunks should have come across before and should know how to resolve rapidly.
In one sense I am not surprised by the provider problems. For years, networking staff could not distinguish between a T1 and PRI connection even though neither technology was new. Why should the implementations of SIP trunking keep the same problems resurfacing even though SIP trunks are relatively commonplace today?
The third question is "If you had problems that were found to be on the Edge/SBC device, what were they?"
The responses to the eight possible choices in the chart above demonstrate that the problems are over the map. Most of these problems should never have occurred.
Registration failures are high as well as "Firmware update required". It is possible that the "Firmware" problem could be associated with the SBC Failure Crash/Lock-up problems. These problems can be easily resolved. Consider that firmware should be applied before going live.
No Audio/One Way Audio problems feature strongly as major issues. These problems highlight the importance of testing the elements together before deploying. Results of such testing could affect procurement decisions of edge devices.
The SIP survey report finished with some recommendations:
* Locate and talk to people about their installation experiences and discuss the problems they have encountered and how they resolved them.
* Verify that the provider covers everything you need, from Service Level Agreements (SLAs) to support for the small sites in remote locations.
* One factor that really stands out is the need for correct documentation that supports the PBX configuration and the SBC/Edge device in order to ensure that the SIP Trunks register and operate correctly.
* Continually monitor the SIP trunk performance. Ensure that when any software upgrades are implemented on the PBX or SBC that these upgrades do not affect service.
