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Connecting contact centers with SIP trunking

Irwin Lazar, Nemertes Research

Session Initiation Protocol (SIP) is improving call center agent productivity and also playing a role at the back-end of the contact center, as architects seek to leverage emerging SIP-based services to reduce operating costs and deliver additional design flexibility. Nemertes Research found that 96% of all companies are now deploying, planning to deploy or evaluating SIP trunking. So it's no wonder that contact center managers are evaluating opportunities to improve operational efficiency via SIP-based services.

Advantages of SIP trunking

The benefits of SIP trunking in the contact center are many. They include:

  • Flexible design: Several organizations that see large changes in call volume based on time of year (such as Mother's Day or Christmas) are changing their current public telephone network connectivity model -- based on buying and maintaining sufficient trunk capacity for peak times, and paying for that access all year long -- to a SIP-based model. This model allows them to turn up and turn down capacity as needed by simply adding or subtracting additional bandwidth to and from their IP connection to their service provider.

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  • Resiliency: As an IP-based service, SIP trunking supports disaster recovery and fail-over scenarios better than traditional services, enabling contact center architects to roll calls over to secondary locations in time of failure, or peak load.
  • Hosted SIP-based applications: Companies such as Voxeo and others are delivering cloud-based UC applications, such as interactive voice response (IVR), that customers can integrate with their own on-premise systems via SIP trunk. Leveraging cloud-based services via SIP reduces development time and both development and maintenance costs.

Challenges of SIP trunking to the contact center

Getting to a SIP-enabled contact center isn't without its challenges. Those implementing SIP should be aware of the following SIP trunking challenges and requirements:

  • Adequate training: IT executives are experiencing challenges in finding personnel trained in SIP implementation and management. Concerns extend beyond hiring their own staff to finding qualified service providers, consultants and even vendor engineers. Successful SIP implementations require cross training between telecommunications and network teams to understand the inner-workings of SIP and how it enables contact center infrastructure.
  • Management tools: IT architects cite the need to deploy tools that allow them to manage and troubleshoot performance of SIP for both SIP trunking as well as for internetworking of SIP-based systems. In many cases, network engineers still rely on packet capture and manual examination of flows to determine problems, a long and arduous task that requires technicians to possesses not only a solid understanding of SIP message flows, but also vendor proprietary extensions to SIP. Management tools provide performance data on user-defined metrics.
  • Compression: In a one-for-one replacement of TDM public telephone network trunks with SIP trunks, bandwidth costs for SIP trunking can exceed TDM costs due to the additional overhead required for SIP, compared with 64 Kbps channels for TDM voice. Growing use of high-quality compression algorithms, such as the International Telecommunications Union's G.722 and G.729 algorithms, will allow SIP trunking adopters to reduce VoIP bandwidth requirements.
  • SIP trunk security: SIP trunking creates a new vector for attacking enterprise phone systems. In most VoIP architectures, the public telephone network serves as a firebreak between the enterprise phone system and the rest of the world. Risk of attack from the Internet is low, because the VoIP and contact center system is physically and potentially logically isolated from the outside. Introducing SIP trunking changes this, because the phone system is now vulnerable to IP-based attacks via the SIP trunk. Session border controllers or SIP-aware firewalls can mitigate security concerns.
  • Eavesdropping: VoIP traffic carried via SIP trunk across a service provider network is often not encrypted, meaning that the opportunity exists for a rouge person to listen in on private contact center conversations via service provider networks. However, this threat is no different than the risk of unauthorized interception of any unencrypted IP traffic carried across a service provider network.
  • Lack of usable fax services: Fax over IP has always been the thorn in the side of VoIP. While most VoIP vendors support the International Telecommunications Union T.38 standard to enable fax over IP, support for fax has not yet materialized in the SIP trunking market, and interoperability among T.38-based solutions is problematic. Even though fax volumes continue to decline, fax is still a key requirement for contact centers that use contracts. Companies often address fax over IP by deploying fax-to-email solutions for in-bound reception, or by using scanners or fax machines connected to public telephone lines for outbound faxing, the latter resulting in additional cost and complexity.

Although there are challenges, none of them are true roadblocks on the path to contact center SIP. Contact center architects should address these concerns as they look to leverage the power of SIP to improve services, support unified communications, reduce costs and improve design flexibility.


About the author:

Irwin Lazar is the vice president for communications and collaboration research at Nemertes Research, where he develops and manages research projects, develops cost models, conducts strategic seminars and advises clients. Irwin is responsible for benchmarking the adoption and use of emerging technologies in the enterprise in areas including VoIP, unified communications, video conferencing, social computing, collaboration and advanced network services.


This was first published in October 2010

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