Top 5 SIP-Trunking Gotchas!


In 2009 Nemertes interviewed about 200 IT executives to gather data around their IT initiatives. One of our many goals was to separate SIP trunking reality from hype. What we found confirmed our initial hypothesis: interest in SIP trunking was growing, early adopters were experiencing success, but many also were facing challenges. We’ve just wrapped up another round of interviews and while we’re still in the early stages of analyzing the data, we’ve identified a number of key “gotchas” that those implementing SIP trunking have identified. 1. Interoperability. We hear concerns around interoperability time and time again. Despite the SIPconnect 1.0 standard, despite vendor pledges of interoperability and numerous certification programs, adopters still tell us that their biggest issue is simply overcoming interoperability issues between their current PBXs and their SIP trunking provider. Often they find out after they’ve begun implementation that they needed software upgrades, gateways, or session border controllers. We’ve heard stories of varying support for SIP interfaces; some providers deploy an integrated access device that converts their own SIP service to a TDM interface going to the customer PBX. Others support direct SIP connectivity (perhaps with an SBC for security). In some cases the choice of provider architecture breaks features such as the ability for a local IP-PBX to fail over to a remote server. 2. Applications and Legacy services. Common concerns heard include the inability of SIP trunking services to support fax, dial-up modems, and call recording software or other customized contact center applications. Again these issues tend to rear their heads after deployments have started. E.911 service support isn’t widely available as well. 3. Architecture. Those seeing the biggest benefits from SIP trunking don’t simply replace their existing PSTN trunks at all locations with an equal number of SIP trunks; rather they deploy SIP trunking as part of a move to a centralized architecture. This approach allows architects to reduce the number of trunks, take advantage of bursting services, and more easily support distribution of calls into multiple data centers. A centralization strategy often entails deployment of session management or some other means of unifying disparate systems. 4. Management. We still hear concerns around performance management. Vendors and service providers are still coming up to speed in their ability to troubleshoot and proactively manage SIP trunking services, as well as their ability to enforce SLAs covering up-time, call completion and call quality. 5. Design. In a one-for-one replacement of TDM PSTN trunks with SIP trunks, bandwidth costs for SIP trunking actually exceeded 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 ITU G.722 and G.729 will allow SIP trunking adopters to reduce bandwidth requirements. Despite all these concerns I expect that our data will show SIP trunking interest is continuing to grow. Those of you responsible for telecom strategy should continue to evaluate SIP trunking services, especially as part of your overall WAN and mobility strategy, but pay special attention to the concerns I raised in this list; doing so will save you a great deal of headaches down the road.


Copyright © 2010 IDG Communications, Inc.

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