Shrinking idle capacity: Corporate SIP trunks could equal T-1 links by 2015

The percentage of North American companies using SIP or Session Initiation Protocol trunking and traditional T-1s will just about equalize in two years, marking a dramatic shift in technology used for external corporate communications.

Of the 278 companies responding to an Infonetics Research survey, 58% say they will use at least some SIP trunks in 2015 while 55% say they will use will use at least some T-1s.

SIP trunking involves connecting all corporate voice, video and data traffic to service providers' networks over a single IP connection. This removes the need for dedicated circuits to handle each type of traffic, thereby making more efficient use of bandwidth and lowering costs. The inherent nature of IP allows for routing traffic around failures, so if the connection to a single corporate site is downed, for example, the corporate IP phone network can be kept alive from another site.

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That's a dramatic shift from today, when 38% use SIP trunking and 71% use T-1s.

The big motivations for the shift are lower costs and better reliability, says Diane Myers, an Infonetics analyst who wrote "SIP Trunking and SBC Strategies: North American Enterprise Survey."

Even more might be shifting over to SIP but they are happy with their current voice services and their current contracts extend beyond 2015, the study says.

While SIP trunking is making clear gains, it won't wipe out use of T-1 and ISDN trunks, she says. "[T]here isn't going to be a 100% cutover from T1 to SIP. Companies are using SIP trunking for only a portion of their call capacity," Myers says.

When asked what SIP service providers they use or are considering, respondents to the survey named more than 20, which indicates that competition is stiff and there is no dominant carrier, the survey says.

The survey was conducted among 278 organizations with more than 100 employees.

Tim Greene covers Microsoft and unified communications for Network World and writes the Mostly Microsoft blog. Reach him at and follow him on Twitter @Tim_Greene.

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