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January 29, 2010 • Vol.32 Issue 3
Page(s) 36 in print issue

SIP Trunking On The Rise
The Advantages & Drawbacks

Key Points

• SIP trunks can bring data, video, and voice into an enterprise over the same line, saving costs in the process.

• Implementing a SIP trunk doesn’t need to be difficult; often it means bringing in a new server.

• An enterprise will need to upgrade to special VoIP phones when installing a SIP trunk. Be sure to consider those costs, as well.

SIP trunking is on the rise with enterprise buyers looking to lower expenses, according to a 2009 Infonetics Research survey. Experts agree that making the move to SIP makes good economic sense, but is it a good option for many SMEs?

Mike Oeth, CEO at VoIP communication service provider Junction Networks (, says enterprise buyers need to weigh the advantages and disadvantages of SIP trunking to determine whether it fits their needs.

The SIP trunk essentially lets enterprises use VoIP with their PBX systems. SIP is a standard by which the trunk operates. So a SIP trunking device acts as a translator between an enterprise’s legacy phone system and its Internet connection.

In terms of popularity, the Infonetics Research survey revealed that SIP trunking is catching up with traditional TDM services, says Matthias Machowinski, Infonetics Research’s directing analyst for enterprise voice and data.

Survey results found that the average enterprise spends between $100,000 and $500,000 per year on trunking services. Although T1 lines are still the most commonly used trunking service to connect to the PSTN, native VoIP trunks are on the rise.

“Many companies have already deployed VoIP internally, but they usually use legacy technologies to connect to the PSTN,” Machowinski says. “In our latest study, we finally see this changing. SIP trunking is catching up with legacy services and gaining broad traction with buyers driven by their desire to lower their overall trunking expenditures.”

A Money-Saver

Enterprises can save money using the trunk, because it can carry voice, data, and multimedia apps over a single conduit, according to Paul Marra, vice president of voice products at MegaPath (, a provider of Internet protocol communications. This reduces monthly expenses because only one connection for data and voice is needed, Marra adds.

“There’s no limit to the amount of calls that can be sent over the SIP trunk, and data can come through that same pipe,” he says.

Still, even with its potential cost savings, Machowinski doesn’t expect to see SMEs rushing to deploy SIP trunking. “SIP trunks are usually implemented during general technology upgrades, which are on hold at many companies right now,” he says.

Necessary Elements

When an enterprise uses a SIP trunk, Oeth says it must also maintain an IP-based PBX, which can be a server that allows SIP capability, or it can be a traditional digital or analog PBX with an interface for SIP trunking.

“But a small company with good internal IT resources could take a server and put software on it [and] then buy VoIP phones and hook them up with a service provider to provide the dial tone,” he says.

That move would give an enterprise VoIP, with services that include dial-by-name directories and conferencing abilities, for the cost of a server, Oeth adds.

Also required for a SIP trunk is what’s called a border element to facilitate connection between the enterprise’s IP network, the PSTN, and an external IP-carrier network. Border elements are usually managed by the Internet telephony service provider needed to connect the enterprise to the public switched telephone network, Marra says.

So while SIP trunking expenses are low, the enterprise will need IT staff that can set up and maintain the server, Oeth says.

But special server expertise is not usually required, Marra adds. In fact, IT staffers trained on server setup and maintenance likely can handle the job.

“A lot of these guys, even if they’re not voice guys, really come up to speed quickly,” he says.

Enterprises considering SIP trunking should price that method against the VoIP hosted service model, Marra says.

“Hosted services can be more expensive because it’s a per-seat model and in trunking it’s a shared-cost model,” he says. “In a hosted model, you’re paying a monthly fee.”

Of course, the hosted-service model has advantages, as well.

“With hosted, you’re maintaining nothing while still getting feature-rich calling options,” Oeth says.

Been There, Done That

Bill Lynch, Aspect senior director of infrastructure services, is in the perfect position to speak about SIP trunking pros and cons. His company finished a SIP trunk implementation at its company headquarters in Chelmsford, Mass.

Another SIP trunk in England provides those services to company offices in Europe. Now, the 1,700-employee company is on target to save $1.2 million during the first year of implementation.

“Before SIP trunking, we had multiple sites around the world with PBX and circuits running into them,” Lynch says. “To retire all those environments was a huge cost savings.”

Also, employees got to keep their local numbers, which is no small thing to clients who may have been dialing the same number for years, and for employees who may be emotionally tied to their particular phone number. They won’t need to have new business cards printed, either.

But the move hasn’t come without some hardship, Lynch adds. In the old days, should a PBX system go down, the enterprise lost phone calls only to and from that office location.

“Now we have all our eggs in one basket,” Lynch says. “If you lose one hub you lose calls for all of North America. So we really had to invest in hardening our environment.”

He recommends enterprises looking to implement a SIP trunk install high-availability circuits, which minimize the risk of outages.

During implementation, his company also realized that some IT techs were unfamiliar with the border technology.

“Those things are very new to the industry and new to us and not as well known as old telephony systems and routers, so we had some challenges in setup and configuration and support,” he says. “Be aware that technical folks could need to spend a good deal of time researching it.”

Bottom line? As in all things IT, no one size fits all, Oeth says.

“You’re going to have to compare hosted VoIP to SIP trunk to traditional landlines and everything else to really see what’s right for your company, no matter the size,” he says.

by Jean Thilmany

Same Number

Bill Lynch, senior director of infrastructure services at Aspect, found an unexpected benefit to implementing a SIP trunk at the company’s European headquarters in England. Phone numbers could stay the same and remain local.

“That was extremely important in Europe because folks in Italy didn’t want phone numbers based out of England,” Lynch says. “With the SIP trunk, we could port numbers to those circuits to give the appearance of making a call out of your home country.”

“Culturally, we’re all one country,” he says.

The regional telephone number is of lesser importance to Aspect’s U.S. employees.

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