SIP It’s More Than What You Do with a Hot Chocolate

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 traditional landline service also known as TDM (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 “a standard protocol for initiating an interactive user session [in English, a phone call, data transmission, or video transmission].  SIP can enable all sorts of connections between devices while providing great flexibility to its users (more info here.) Bottom line: the underlying technology offers great flexibility and capability, although it’s not without limitation. Before taking the plunge, it’s critical that decision makers 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 or circuits will continue to increase, as the number of traditional TDM trunks or circuits 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 number of business customers are likely to base their communication architectures on greater amounts of Internet bandwidth and capacity as part of an overall network plan that supports multiple communications components (voice, data, video) rather than investing in SIP trunks as a separate, partitioned, and unshared communication facility.  Finally, consensus is that overall network architectures are changing with SIP being a critical-- but not the sole--underlying technology.
 
For any number of good reasons, traditional circuits that have supported business communications (historically supporting only voice and fax) are gracefully making way for more sophisticated technologies that can support multiple types of communication (voice, video and data) over a single large communications pipe.  Because the cost of maintenance and replacement of this old technology 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 (local phone company hubs) support SIP consistently.  In addition, SIP’s technical limitations may prevent it from allowing inbound direct inward dialing (DID-calling an “in house” number directly instead of going through a switchboard) 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). UC is a frequently heard buzzword that is used to describe “all forms of call and multimedia/cross-media message-management functions controlled by an individual user for both business and social purposes.”  Limitations on support of UC are relevant if your firm is considering a long-term plan.

There is no question that internet bandwidth is becoming not only increasingly valuable, but also 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 internet-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 enterprise/end users must 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 trying to sell my client.  For the record, my client didn’t buy.