Martha Buyer
Martha Buyer is an attorney whose practice is limited to the practice of telecommunications law. In this capacity, she has...
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Martha Buyer | January 25, 2016 |


SIP: It's More than What You Do with a Manhattan

SIP: It's More than What You Do with a Manhattan SIP is impressive, but it is not without limitations, and as such, is not the answer to all questions.

SIP is impressive, but it is not without limitations, and as such, is not the answer to all questions.

While the number of traditional landlines in the U.S. and North America is decreasing, the fact remains that they're not totally disappearing. And as much as an aggressive sales person may tell you that the time for TDM (standing for "time division multiplexing") has come and gone and that it's going the way of the -- hmmm...vinyl record? (no, they're back) ... cheap gas? (no, that's back too) ... the empty plane flying to your destination (I fear that's NEVER coming back). The sales person who pushes a newer and very capable technology called "SIP" (for "session initiated protocol") is overselling if he/she tells the customer that it will be the only way going forward.

SIP is defined as "an Internet Engineering Task Force (IETF) standard protocol for initiating an interactive user session that involves multimedia elements such as video, voice, chat, gaming, and virtual reality. ... SIP can establish multimedia sessions or Internet telephony calls, and modify, or terminate them. The protocol can also invite participants to unicast or multicast sessions that do not necessarily involve the initiator. Because the SIP supports name mapping and redirection services, it makes it possible for users to initiate and receive communications and services from any location, and for networks to identify the users wherever they are." (Go here for additional technical information). Bottom line: The underlying technology offers great flexibility and capability, although it's not without limitation. Before taking the plunge, make sure you understand what those vulnerabilities are because they can force unhappy changes for the unprepared consumer.

Recently, a very smart and tech-savvy client of mine had this experience. He was told by one well-known SIP provider (of course) that in the next five years, 92.7% of new phone lines in the U.S. will be SIP. In response to his query about the validity of this statement, I both researched on my own and reached out to my consultant network for members' feedback for an answer. The short answer is that the vendor's numbers are aggressive by any possible calculation. The percentage of SIP trunks will continue to increase, as the number of TDM trunks decreases, but 92% is as crazy a number as is the thought that TDM circuits will disappear entirely. Neither is likely to happen.

What is likely to happen, however, is that an increasing numbers of enterprise customers are likely to base their communication architectures on expansions of Internet bandwidth as part of a converged network plan rather than investing in SIP trunks as a separate, partitioned, and unshared communication facility. Finally, consensus is that network architectures are changing with SIP being a critical -- but not the sole -- underlying technology.


For any number of good reasons, TDM is gracefully making its way into the sunset. It's not going to go below the horizon any time soon, despite the claims of those who are selling other services, but because the cost of maintenance and replacement is so high, and because of the capabilities that other IP-technologies offer, the portion of the market that relies on TDM is gracefully stepping back, although not disappearing completely.

SIP does not -- and cannot -- provide all of the services that TDM does. Considering a 1:1 replacement is not a good plan by any measure. First of all, not all central offices support SIP consistently. In addition, SIP's technical limitations may prevent it from supporting such basic services as support for inbound direct inward dialing (DID) and circuit failover options that are readily available with TDM.

SIP Vulnerabilities and Limitations

In a nutshell, SIP does not fully support unified communications (UC). Limitations on supporting UC are relevant if your firm is considering a long-term plan. Specifically, UC requires higher bandwidth SIP channels for video-over-IP sessions. UC requires lower bandwidth IP sessions for presence and IM, and irregular bandwidth for desktop image and application sharing. I know this is highly technical, but it remains an important consideration if you're considering a technology migration.

There is no question that Internet bandwidth is becoming not only increasingly valuable, but also increasingly available. As provided by Ethernet-based IP backbone providers, it's also becoming increasingly cost-effective. According to UC guru Marty Parker, "The consequence is that increasing numbers of enterprise customers are likely to base their communication architectures on expansions of their Internet bandwidth as part of a converged network plan rather than investing in SIP trunks as a separate, partitioned, and unshared communication facility."

SIP trunking creates the same types of problems as do all IP-based communications systems -- 911 information, particularly with respect to both location and number identification, is not reliable. As such, providers will force customers (or they should force customers) to acknowledge the vulnerability in this infrastructure element, and those enterprises/end users should be forced to address 911 obligations independently of the service provider. That's not to say that it can't be done, but it won't be automatic -- or readily accessible -- as it has been with TDM. It's important to build these costs into any system configuration change because while the underlying technology may not be well-suited to providing this information, the employer still retains its OSHA and other mandates to provide a safe workplace for employees, consultants, and guests. That is, save budget room because compliance where it's required by law, or simply good judgment, can be costly.

One final point: SIP is a signaling/call protocol, not a transport protocol. What makes SIP impressive is its ability to set up connections among and between voice, video, and other devices and recognize the most efficient path available. But it is not without limitations, and as such, is not the answer to all questions. It's also not likely to achieve that 92.7% benchmark quoted by a vendor interested in selling my client. As a final note, my client didn't buy.

Learn more about SIP and SIP trunking at Enterprise Connect 2016, March 7 to 10, in Orlando, Fla. View the SIP/SIP Trunking track sessions; register now using the code NJPOST to receive $200 off the current conference price.


Enterprise Connect Orlando 2018
March 12-15 | Orlando, FL

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