Thoughts from the SIP Trunking Road Show
SIP Trunking is maturing. The lack of standard implementations has slowed adoption, though I fully expect the pace to accelerate given the cost savings and support of technologies such as UC and video.
SIP Trunking proved to be a popular topic at the recent Enterprise Connect four-city Road Show and Virtual Event. The tour attracted enterprises that were considering this "new" technology but hadn't yet deployed it. At three of the four tour stops, I presented a session on the status of the SIP Trunking world and facilitated a panel of industry providers. (At the fourth Tour stop, Las Vegas, these sessions were handled by Jim Allen, who has delivered a portion of the SIP Trunking tutorial at the past 2 Enterprise Connect Orlando shows.)
This article is based on the high- level common themes and questions from the tour as well as what I see on a day-to-day basis from an end user consultant's perspective.
Truth or Myth
SIP is new--Myth (mostly): SIP has existed in some form (earliest RFC I could find is 1996), though most in the industry are familiar with implementations for endpoints (i.e. SIP phones) or as the protocol of choice for integrating UC components. RFC 4904 (June 2007) largely defines SIP trunking, so it's been around at least for five years.
SIP Trunking is Standardized--Myth: Although there are several RFCs supporting SIP, as well as the recently adopted SipConnect 1.1 specification from the SIP Forum, significant differences exist in implementations from various carriers and equipment manufacturers (i.e. IP-PBX, gateways, SBCs). In addition to the technical differences, carriers have bundled features and options differently so as to make comparisons among their SIP trunks more challenging (than is the case for PRIs).
SIP Trunking is "Mature"--(Partly True): It's kind of like a teenager, behaving the way you expect it to sometimes and surprising you often. This is particularly true in the provisioning and implementation phases. When compared to the system that supports PRIs, the tribal knowledge of personal and actual systems at the carriers isn't quite fully baked when it comes to SIP Trunking.
SIP Trunking offers Cost Savings--True: Though as the saying goes, "Your mileage may vary". Savings in the range of 30-50% are possible for large distributed environments that adopt a centralized SIP Trunking model. Smaller savings in the 10-15% range are possible for smaller environments doing a like-for-like SIP/PRI replacement.
I don't need a Session Border Controller (SBC)--False: Almost every IP-PBX provider is able to support SIP Trunking natively via supported gateways and Session Management. In addition, carriers provide SBCs on their side of the SIP trunk. Although the statements above are true, Enterprises are encouraged to procure their own highly available SBC for the following reasons:
* Security--Enterprise SBC acts as an Application Aware Firewall for SIP communications
* Protocol Interoperability--between different implementations of SIP (and possibly other protocols such as H.323)
* Handling multiple carriers
* Dial Plan Support
SIP Trunking is widely Available--True: SIP trunking is available in most metropolitan areas directly from Tier 1 and Tier 2 carriers. In addition, SIP Trunking is available almost everywhere from "over the top" implementations.
There is one model to implement SIP Trunking--False: A couple of years ago, this might have been considered a true statement, as a "Centralized" architecture (i.e., a single SIP trunk at the datacenter, aggregating all traffic destined for the public network) was touted as the way to go. Whereas this still is the most popular approach, offering the highest cost savings as well as dial plan centralization, two other models have come into the picture: Distributed and Hybrid. The Distributed model allows for quicker implementations by keeping the dial plan somewhat intact. It also offers a better use of network resources if Video will be used heavily by the enterprise (i.e., avoids hairpinning and trunk saturation). Hybrid of course combines properties of both Centralized and Distributed, customized for the specific needs of an organization. International implementations typically use the hybrid approach.
Below are diagrams highlighting the Centralized and Distributed Approaches:
SIP Trunking is maturing as industry. The lack of standard implementations has slowed adoption, though I fully expect the pace to accelerate given the cost savings and support of technologies such as UC and video. The use of SBCs allows the enterprise to mitigate the current shortcomings. Piloting and rigorous testing is still required, as is the case with most new technologies.
Dave Stein is an independent consultant and principal of Stein Technology Group.