There are surprises and there are surprises. For instance, I like it when I come home after a long day at work to find that my wife made dinner reservations at my favorite Saint Paul restaurant – W. A. Frost. I also like it when I finish my tax returns and discover that I don’t owe thousands of dollars in unpaid taxes. Believe me, I have been surprised in the opposite direction several times and can do without that kind of excitement.
However, I don’t like getting surprised at work. Those surprises generally involve more toil, looking foolish, less money, longer hours, or all of the above. The looking foolish part happened to me recently,but instead of moping about it, I decided to use it as a teaching tool.
I recently began working with a company and their carrier on adding SIP trunks to an Avaya PBX. Unfortunately, I was brought into the project late in the game and quite a bit of discussion had already occurred. Perhaps I was told all the details or perhaps I was not, but the result was that I was under a few false assumptions about what the customer wanted and what the carrier was set to deliver.
Specifically, it turned out that yes, SIP trunks were being deployed, but the customer wasn’t actually setup to work with direct SIP. The carrier, which happens to be Verizon, was providing the SIP, but the SIP was terminating on a Cisco 2911 router configured as a SIP-to-PRI gateway. So, SIP to the demark point and ISDN to the customer’s communications system.
It’s no wonder that I couldn’t get straight answers about session border controllers and session managers. There weren’t any and the customer wasn’t about to deploy them.
Now, if I were an unscrupulous sales guy, I might try and tell the customer that he was making a bad decision and upsell him on equipment that he wasn’t ready to deploy, but thankfully I am neither a sales guy nor unscrupulous. Instead, I embraced this as a viable solution that will serve the customer well until he is ready to move a little deeper into SIP.
There are situations where SIP, at least total SIP immersion, is not the best answer. A business may have a number of good reasons why it wants to dip its toes into the SIP stream, but it wants to do so in a measured and controlled manner. It wants to reap some of the benefits of SIP, but is fully conscious of what it can and cannot afford.
This particular business has an Avaya system that has been kept up-to-date software and hardware-wise, but is still predominately TDM. They understand the benefits of VoIP, but haven’t invested in a VoIP-ready network. Additionally, the nature of this business is not one that has Ethernet cables where they are needed for telephony. Although antiquated by today’s standards, analog and digital telephones are still in wide use by many businesses. This business needed a compelling reason to change and until they got it, things were staying put.
Still, they wanted to take advantage of some of the benefits of SIP and SIP trunks are a great place to start. They can eliminate many of their costly ISDN trunks, create a better business continuity strategy, consolidate networks, and take the first step towards what may ultimately be a much larger leap into SIP.
Baby Steps
So, the idea of bringing in those SIP trunks, running them through a SIP-to-PRI gateway, and terminating T1s on their existing line cards is a perfectly good choice. One day they may decide to take things a little further, but other than having to re-purpose a fairly inexpensive Cisco router, they haven’t thrown good money at bad.
Later on, they can move those SIP trunks away from the 2911 to an SBC without having to completely redesign their SIP solution. SIP is flexible enough to support quite a few of these transition solutions. That Cisco router could just as easily have been one of the many SIP-to-TDM gateways offered by AudioCodes.
In the end, my surprise turned out just fine. Granted, I was a little confused for a while, but that’s nothing new. Once I understood what was what, I was able to assist Verizon with their implementation questions and get the customer rolling down the road to SIP. That’s the kind of work surprise I can deal with.
Tao, Zen, and Tomorrow 
I know this is 3 years old I saw your article and find myself in a similar situation. I have a client with a Old Avaya TDM Spectel CS700. That wants to SIP to TDM they want to use Cisco 5400 as gateway to terminate to there DS3 line cards. SIP-5400-TDM people have done it but it’s my first time and just wanted to know how it worked for you