SIP - Is it the 'nirvana' of interoperability?


When I sat down to write my blog on UC, I had many thoughts going through my head about new hardware and new innovations that people would be interested in. However, after leaving a customer meeting, I thought it better to try to stress a more common issue that a lot of people seem to be completely oblivious to – SIP interoperability.

So over the weekend, whilst visiting my parents in Newcastle, I sat with the keyboard clattering (two fingers at a time!). I set about the task of addressing this great misnomer over SIP (Session Initiation Protocol) integrations and how SIP is the nirvana of the communications world. Three pages later, my job was done. Dickens would have been impressed … but not my nephew!

My nephew looked over my shoulder and commented on the madness of working on a Sunday afternoon (Boss, please note) and asked what I was doing?

He's 15, I thought, so if I can make him understand, then I should be able to make most people understand … so off I went!

I checking that he knew that the internet ran on this thing called IP and that there were a few different languages, like H.323 or SIP. I checked he was happy knowing that a language was needed so devices would to be able to understand each other and that this thing called SIP was just a way of two bits of equipment talking to each other, using the same language.

Now at this point I foolishly said … “so SIP, as a language, might be like English and as long as we both speak the same language we can understand each other. If one of us spoke English and the other French, we'd have problems, right?”

My nephew, very quickly jumped in with, “Uncle Harry speaks English, but I can't understand a word he says!”

In that simple statement he had hit the nail on the head!

Yes, we had all been speaking English that morning, but my nephew is from Cumbria and my uncle Harry is a Geordie and I did remember having to interpret quite a lot. Harry, you see, speaks very fast and in a broad Geordie accent(described by my own daughter as “unintelligible”) so my services were required to make sure the kids knew what he was saying.

Both were speaking English, but their dialects were different !

That is the SIP issue in a nut-shell – differences in version/software/revisions/vendor/etc. means that although both devices are trying to communicate in the same language they can't.

Many people say that they want to use SIP and don't understand the ramifications. There isn't just one version or implementation of SIP. If you want to use a SIP-trunk to connect to the PSTN, you should expect to require some device to interpret – it's called a Session Border Controller (SBC).

The reasons are fairly straight-forward, but often overlooked:

  • The service provider (SP) certainly already has an SBC with customers already connected, so you'll need to put in an SBC on your site to make sure you conform to the SP's requirements and not vice-versa.
  • You're connecting your IP telephony system to the outside world via IP – you need something to make it secure, SBC's offer this advantage
  • SIP is a protocol that is easily adapted, so each end of the communication must support this, if you IP PBX can't you'll need an SBC to interpret.
  • Always plan for a pilot scheme to test and retest.

So my three pages are gone and I leave you with this thought:

If I had to interpret between two people just because of dialect within the same language, how complex could it become when integrating between multiple vendors, with multiple SPs in different countries?

If you've had issues with SIP and SBC implementation, let us know your thoughts!

Nicolas Jacquey
chris habberjam

Chris is an experienced IT professional, specializing in voice communications. His favourite areas are around IPT and Unified Communications.