Feature Story

SIP Trunking Continues Ascent: Interoperability Efforts Move Forward as Well

By Paula Bernier

As the other two stories in this package discuss, SIP-based premises gear has seen gradual adoption, but not the rocket-like growth some had originally forecast; meanwhile, some have questioned whether SIP-based services are ready for prime time. But one aspect of SIP-based communications that has seen very little resistance and very wide appeal is SIP trunking.

According to Irwin Lazar, vice president of communications and collaboration research at Nemertes Research, about 55 percent of companies are either deploying or evaluating SIP trunking.

The Big Sell

The reason for the business world’s interest in SIP trunking is clear: The service is far less expensive than buying PRI lines for voice traffic.

“There hasn’t been a compelling business case for SIP in the enterprise for anything other than interconnection of PBXs,” says Lazar. “Most of the companies we talk to who are doing trunking internally are doing it to save long-distance costs.”

As Rick Pfleger, director of sales engineering at managed service provider VoIP Logic, notes, an average mid-sized company typically uses a T1 for data and a PRI for PBX (News - Alert) voice communications. But moving to SIP trunking can enable the company to get rid of the PRI or PRIs and instead put all of its traffic over a single connection, potentially a bonded copper or fiber-based Ethernet link.

Lazar of Nemertes Research says SIP trunking can produce 20 to 60 percent in savings for a company.

SIP trunking also has some other nice features, says Lazar, adding that companies can leverage the technology to route calls based on time of day or on load and to set up virtual numbers in remote parts of the world.

Optimum (News - Alert) Voice for Business launched its SIP trunking product last summer, says Joe DeLotto, director of product management at the Cablevision company. The initial service, he adds, was somewhat limited, supporting only Cisco and Microsoft (News - Alert) endpoint devices. However, the company is now in the process of expanding its list of supported IP PBXs and expects to announce the details of that effort next month, he says.

DeLotto says beyond the obvious cost savings SIP trunking offers relative to PRIs, which are expensive, moving to this new service delivers a converged solution for customers; can be easily upgraded; offers alternate call routing if an endpoint is not available; and includes call admission control, which has ability to define and control the number of incoming and outcoming calls (this is a useful feature in environments such as inbound call centers).

SIP Connect

As with most new technologies, standards around SIP trunking continue to evolve.

Lazar says there are still a lot of different ways of implementing SIP, and some service providers’ services don’t work with some PBX vendor solutions. But SIP Connect, an initiative from the SIP Forum (News - Alert) that began a couple years ago, is now in version 1.0, which a lot of vendors now support. Version 1.1, expected to be released soon,will help alleviate this interoperability concerns further, he says.

Noting that the IP PBX market is highly fragmented – with Avaya (News - Alert), Cisco, lots of Toshiba, Panasonic and Asterisk gear out there, DeLotto says the cablecos have tried to drive interoperability by pushing for a standard on which equipment providers and service providers can agree. SIP Connect 1.0 out of the SIP Forum, in which DeLotto’s company is a member, never really had a certification program and includes a lot of things that are considered optional, he says. DeLotto describes 1.1 as a tighter spec that will nail down how to implement various aspects of SIP trunking. SIP Connect 1.1 is anticipated to be signed off on by this fall, he adds.


Elsewhere on the SIP networking front, international wholesalers are becoming more interested in moving toward SIP-I and away from traditional TDM connections, according to Veraz Networks.

Dawn Hogh, vice president of marketing at Veraz, says that about a year ago the company was working with the GSMA (News - Alert) on validating its SIP-I work to address this trend. Veraz helped the group define the standard and did some tests around SIP-I, she says, but then the effort – or at least the larger IPX effort of which SIP-I was a part – was put on the backburner. However, according to Hogh, SIP-I has recently made a resurgence.

SIP-I, in which the I stands for interconnection, is a way to carry traditional signaling protocols, like ISUP, over SIP. That means if you’re a wholesaler connecting two companies with ISUP in their networks, you can do that over IP and using SIP. The alternative is to terminate ISUP and then use native SIP – but that scenario involves two conversions, so things can get lost in the process.

Meanwhile, IPX is a service definition the GSMA has been working on that is a model for next-gen wholesale services and includes the use of SIP-I. It also includes descriptions around payment flows and how pricing is done and SLAs.

While a lot of people have looked at IPX and are interested, it will require some fundamental changes in how people think about billing and how payments flow, so it will take a while for wholesale carriers to adopt it, explains Hogh. But in the meantime they can adopt SIP-I right away, she says. IT