SIP vs TDM for the Contact Center

Aimee Giese | August 9, 2016

SIP protocol has been around for years, but it’s been gaining popularity in the contact center space. Why are call centers rushing to convert to SIP?

Frost & Sullivan revealed that the North American VoIP access and SIP trunking services market is expected to expand at a compound annual growth rate of more than 27 percent through 2016, eventually reaching $3.9 billion. TDM (Time-Division Multiplexing) is the legacy protocol for sending voice calls over copper wires. As TDM legacy infrastructures age, more and more are being converted to SIP (Session Internet Protocol), which has the advantage of sending multiple signal types (such as voice, video, chat and multimedia) over a single IP pipeline.

If you’re like me, you don’t have an engineering degree, but you might be charged with having an awareness both of contact center technologies and of opportunities to streamline cost and efficiency of interactions within the contact center. And as contact center infrastructure purchasing changes at its typical glacial rate, at what point do CIOs and CTOs consider the TDM to SIP conversion? And more importantly, what do we really need to know about SIP’s advantages over TDM in the contact center space?

Tdm vs sip graphicWhat is SIP?

SIP is a protocol for controlling and directing communications, including voice, video and data, over IP (Internet Protocol). A good rough analogy would be to see SIP as the voice and data network on your smartphone and TDM as the voice-only, analog experience on a dial home phone. The analogy isn’t entirely accurate, but you get the idea. SIP treats all communication–voice, data, video, instant messaging, whatever– as software, using VoIP technology, and transfers it over IP.

SIP Trunk

What’s cool about SIP isn’t just the IP conversion; SIP Trunking is a single conduit for multimedia elements (voice, video and data) that allows multiple signal types to travel over the same pipeline. This is a huge advantage for call centers that often need to coordinate a voice call with caller data using a screen pop to an agent.

SIP Trunks are used to connect a company’s private switch (Private Branch Exchange or PBX) to the public network using the internet instead of traditional analog phone circuits. SIP Trunking is the de facto standard for VoIP applications. This means that a service provider would offer a SIP trunk to facilitate communication between an organization’s PBX and the public network. Or, I should say, “PBXs,” since with SIP, it’s easy to connect multiple locations to act as a single system. This model is especially effective when the call center utilizes at-home agents.

What does this mean for the contact center? An easier, more reliable, less expensive way to make voice calls and the data that so often must accompany them. That’s why Frost & Sullivan is predicting such expansive growth in the market: with contact centers always seeking greater reliability at a reduced cost, SIP is an easy solution to dealing with the expense and limitations of TDM.

Advantages of SIP over TDM

A quick summary of the basic benefits of SIP for contact centers:

  • Less expensive: Because SIP can easily transfer voice, data and video signals over a single IP conduit, organizations can save on infrastructure costs and on network data and voice costs.
  • More reliable: IP hardware tends to have longer life expectancy than TDM hardware and is considered more reliable. From TelcoDepot: “One of the most compelling reasons why we like IP is that it brings the telephone system into the realm of self-maintenance and removes the need to roll trucks anytime a phone system acts up.” Likewise, IP networks are much easier to manage than TDM networks in order to provide consistent quality of service.
  • Less purchased hardware: SIP does not require the purchase of expensive gateway hardware or installation of phone circuits (such as BRI or PRI) to access the public network–just a broadband pipeline.
  • More flexible: Staying with TDM often requires you to purchase only from your vendor thus limiting you to your vendor’s pricing.
  • Internet standard: SIP is an IETF standard that most vendors will deploy.
    Faster upgrade: Installation and upgrade to SIP trunks is speedy and doesn’t require costly hardware upgrades.

With advantages such as these, it’s hard to see why any contact center wouldn’t convert to SIP. Still, SIP isn’t the be-all and end-all of telephony and data transmission. Rather than make the full switch, some call centers opt to do a partial SIP converstion: accept the incoming call as TDM, convert to SIP for easy data handling, and then convert back to TDM to send to agents, who might not have the broadband strength to accept a SIP call.

What is your take on SIP conversion? Has your call center made the switch? Why or why not?

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