Technical Considerations for SIP Trunking

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Technical Considerations for SIP Trunking

By Steven Johnson, President, Ingate Systems, Inc.  |  March 17, 2014

Before implementing SIP trunking, it is critical to evaluate your local area network  to determine what may be needed ahead of time to ensure a successful VoIP deployment. Ask yourself the following questions to ensure that the deployment goes smoothly, takes minimal time and, of utmost importance, maintains the security of your network.

How good is your Internet connectivity? Voice over IP requires a steady, high-bandwidth connection. Evaluate service provider delivery to the edge. Will there be a separate MPLS network? If so, consider what that may mean for quality and cost.

Are the routers, switches and other components of your network up to the task? Throughputs and congestion points in the network can cause jitter and delay, which result in poor call quality. Before embarking on your SIP trunking installation, be sure that all routers and switches are up to date and provide adequate throughput for the number of sessions that they will need to support.

How mission-critical is voice to your organization? A failover solution may be important to ensure ongoing communications in the case of a networking failure or malfunction.

To host or not to host, that is the question. Hosted SIP trunking services are ideal for organizations that do not have the technical resources to maintain a VoIP solution, and/or those that may grow and need bigger, better solutions that evolve with their success. Several SIP trunking service providers offer hosted solutions, with the key advantage of ongoing upgrades as new technologies are available.

There’s also the question of where to put the PBX (News - Alert) (with a public or private IP address). Here there is only one right answer: on the inside of the firewall with a private IP address. I know of no business that will put its critical network servers on a private IP address. SIP PBXs deliver mission-critical services and deserve to be protected by the firewall and on a private, non-routable IP address.

Will your firewall support SIP? Firewalls are designed to block unrecognized traffic. Unfortunately, traditional network firewalls often do not understand or accept SIP, the standard protocol for SIP trunking and enterprise voice applications. If they do, they may attempt to support the protocol with a rudimentary application layer gateway, which often causes problems with SIP traffic and doesn’t have the capabilities of a proxy solution nor the ability to normalize SIP signaling with a back-to-back user agent. The end result is that the firewall, designed to protect against the unknown, will simply block your voice, or VoIP, traffic or support only one-way media. Make sure you are using either a SIP-capable firewall or an enterprise session border controller that is specifically designed to handle the SIP protocol properly

With proper planning and up-front action, SIP trunking is a better alternative than traditional telephony offering you lower recurring costs and the opportunity to expand to support unified communications for productivity gains.

Steven Johnson (News - Alert) is president at Ingate Systems (

Edited by Stefania Viscusi