Reliability of SIP Trunks

Ask the SIP Trunk Expert

Reliability of SIP Trunks

By Steven Johnson, President, Ingate Systems, Inc.  |  July 01, 2011

This article originally appeared in the July 2011 issue of INTERNET TELEPHONY

A common question about SIP trunk adoption regards reliability. Businesses rely heavily on their voice networks; as such, the standard for reliability needs to be much higher than what’s generally accepted for consumer use.   

SIP signaling has been around for some time, since 1996. It is an RFC standard from the Internet Engineering Task Force. The first enterprise SIP solutions began to appear around 2000. Today, most every IP PBX (News - Alert) manufacturer has a SIP solution.  

The quality of SIP calls can be excellent. Digital packetization of voice has proven to be better than analog. This is because digital packets do not suffer from audio distortions, loss levels and other weaknesses. The quality of voice is directly related to the quality of the network, with the weak link of VoIP being latency in a slow network. A SIP-capable enterprise session border controller with QoS solves this problem.

Adding redundancy to the network is key to ensuring reliability. By installing a second E-SBC along with the primary E-SBC to create a failover pair, this multiple E-SBC distribution creates a resilient and fault-tolerant network to ensure that mission-critical applications such as voice are always available. The backup server might be a machine in another physical location, presumably not vulnerable to anything that would cause the primary host(s) to become unavailable.

SIP trunks are delivered over the Internet, which means that the connection to the Internet itself can potentially be a single point of failure. Using multiple Internet service providers avoids this issue should one connection go down. Also, since a SIP trunk is virtual, many service providers can have a primary and a secondary route, should primary become unavailable. Regardless, your E-SBC should have an option to be connected to a secondary ISP. 

One signal that SIP trunks are indeed ready for prime time is the tremendous growth of SIP trunk adoption by call centers. The significant volume of calls makes cost-effective voice a priority, and since voice is the core of the call center business it has to be reliable.

For more information on this topic, check out our recent webinar “Successfully Deploying Enterprise SIP Trunking: Tools and Techniques for Overcoming Common Roadblocks” at

Steven Johnson (News - Alert) is President of Ingate Systems, Inc. To read more of Steven’s articles, please visit his columnist page.

Edited by Stefania Viscusi