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Challenges of SIP trunking for telecom managers and network admins

The challenges of SIP trunking for network administrators include interoperability and compression issues, service availability, security, SIP trunking architectures, lack of fax services, E-911 support and SIP trunk monitoring tools.

Over the last two years, perhaps no technology has been as enticing to telecom managers as SIP trunking. With dollar...

signs in their eyes, companies are increasingly lured to the promise of SIP trunking to reduce spending on PSTN access -- delivering new services such as managed call routing, virtual phone numbers around the globe and cloud-based IVR, and offering new options for resiliency.

But for early SIP trunking adopters, significant challenges have hampered the realization of promised benefits.

Bandwidth costs for uncompressed SIP trunks can exceed TDM costs because of the additional overhead required for SIP ...
Irwin LazarNemertes Research

As of late 2009, more than 62% of Nemertes Research participants were deploying, planning to deploy, or evaluating SIP trunking. And interest is strong across all company sizes. Those that have deployed SIP trunking report total savings of anywhere between 20% and 60% versus PRI-based approaches for PSTN access.

Satisfaction among adopters was high, but we consistently heard several concerns, including:

  • Architecture
    For those with lots of distributed PBXs or key systems, adopting SIP trunking means deploying SIP-to-PRI gateways or managing large numbers of new trunks. New offerings based on session management can enable creation of a SIP-based layer between existing systems and SIP trunking services, allowing a smoother and cheaper SIP trunking implementation.
  • Service availability
    Service availability varies widely by region and by carrier service availability. We often hear of concerns that service providers are dragging their feet in delivering SIP trunking to areas where they may cannibalize their existing PRI revenues, or concerns that SIP trunking isn't available in smaller markets. Learn more about evaluating and managing telecom carrier services, including SIP handoffs, in this tutorial.
  • Interoperability
    We still hear concerns about interoperability between service providers and IP-PBX vendors, though increasing certification agreements and the SIP Forum's SIPconnect certification program are alleviating these problems.
  • Training
    IT shops are struggling to train their own staff or find qualified VARs, consultants, and even vendor engineers well versed in SIP implementation, troubleshooting and management. Find out more about writing solid unified communications RFPs and negotiating with VARs in this complete guide.

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SIP compliance doesn't mean unified communications interoperability

Back to basics: SIP tutorial

Dynamic IP routing and routing protocols

What are media gateways and how do H.323, SIP, MGCP and other support protocols work?

IVR and disaster recovery


  • Lack of SIP trunking management tools
    IT architects cite the lack of tools to allow them to manage and troubleshoot performance of SIP trunking services.
  • Need for compression
    In a one-for-one replacement of TDM PSTN trunks with SIP trunks, bandwidth costs for uncompressed SIP trunks can exceed TDM costs because of the additional overhead required for SIP compared with TDM. Find out how voice compression can save bandwidth.
  • Security
    Introducing SIP trunking means that the enterprise phone system is now vulnerable to IP-based attacks via the SIP trunk. Session border controllers or SIP-aware firewalls can mitigate SIP trunk security concerns.
  • Lack of usable fax services
    Fax over IP (FoIP) has always been the thorn in the side of VoIP. Support for fax has not yet materialized in the SIP trunking market.
  • E-911
    While some SIP trunking providers support E-911 services, IT executives still face significant challenges passing location information on to local PSAPs (Public Safety Answering Points) owing to integration issues with SIP trunking and their E-911 architectures.

Key issues include the inability of SIP trunking providers to pass location information to E-911 call routing services. Most SIP trunking providers are limited in their service areas, meaning that they can't route E-911 calls to local emergency services offices out of their operating locations. IT architects often rely on local POTS lines for 911 access, as with fax, adding additional cost and complexity.

Despite these concerns, companies we work with are still bullish on SIP trunking. Adopters are indeed realizing cost savings, are largely finding acceptable service reliability, and are excited about expanding their use of SIP trunking adoption.

Still, a successful deployment means understanding and mitigating the potholes in the road to success.

About the author:
Irwin Lazar, Nemertes ResearchIrwin 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 (UC), video conferencing, social computing, collaboration, and advanced network services.

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