To SIP or not to SIP

Spoken | August 9, 2016

SIP trunking is becoming the telephony protocol du jour in call centers. But is SIP trunking worth the integration headaches?

We’ve discussed the basic differences between SIP and TDM before. Briefly, SIP is a protocol for controlling and directing communications, including voice, video and data, over IP (Internet Protocol). The advantages include the ability to deliver high-definition video and related call data along with call audio over a single pipe as well as an inherent flexibilty and cost savings.

But is SIP all it’s cracked up to be? In a recent report, we believe that Forrester principal analyst Art Schoeller gave SIP trunking a qualified “yes” under the title SIP Trunking May Save You Money (Forrester Research, Inc., August 2011). Because let’s face it: upgrading call center infrastructure is a lofty undertaking, and most organizations won’t do so without substantial proven benefits, which must include cost savings.

So why migrate to SIP?

The report cites the following:

  • SIP trunking will displace T1 and primary rate interface (PRI)
    circuits.
  • The cost savings for enterprises can range from 25% to 35%
    over traditional T1 and PRI access.
  • Over time, SIP-based signaling and VoIP will ultimately
    replace circuit switched technology for carrier access.
  • SIP signaling occurs over trunked lines, which is critical for future advanced signaling operations such as high-definition video and audio.

Screen Shot 2012-10-01 at 3.38.35 PMThat being said, Forrester reports that the American rate of SIP adoption is relatively low, with forty-three percent of enterprises reporting they are not interested or have no specific plans to deploy SIP.

So what’s the holdup?

  • Packetized voice quality. SIP trunking packetizes voice using the G.711 or G.729 codecs, and this can affect speech recognition and other applications that depend on voice quality to operate effectively.
  • Interoperability. Carriers may or may not effectively manage the interoperability between their networks and others.
  • Lack of carrier response.
    From the report: “Forrester has observed that enterprises wanting to move to SIP trunking have found
    their incumbent service providers were slow to respond and provided less aggressive pricing.This is understandable because SIP trunks cannibalize their existing T1 and PRI revenue and
    margins.”

Conclusion and quick tips

In spite of the challenges, the report still concludes “SIP trunking provides a good business case despite the risks that we document above.” Additional advice for those considering the move to SIP is to be assured of geographically diverse failover and alternate routing to mitigate the downtime risk and to avoid unnecessary compression on a single pipe. A few additional tips:

  • Session Border Controllers are absolutely a necessity as a known service control point to manage traffic. Never skip the SBC.
  • Mid-call codec switching can help with voice compression issues. Use high-quality, lower-compression codec for the IVR portion of the call to maximize speech recognition, which requires higher voice quality. Then switch to the lower codec mid-call for the agent transfer.
  • The “final mile” issue. The “final mile” refers to the final leg of the voice journey, which is into the at-home agent’s home. Because bandwidth to individual homes will always fluctuate, try individual testing and be prepared to switch back to TDM if SIP doesn’t provide adequate results.

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