TMCnet - World's Largest Communications and Technology Community



tmc logo
July 2009 | Volume 12 / Number 7
Ask the SIP Trunk Expert

SIP Trunking with a Legacy PBX

To date, most SIP trunking providers and resellers have focused on the opportunity to migrate business customers from PSTN service in concert with an upgrade to a SIP-ready IP-PBX (News - Alert) system. While this focus remains logical and compelling, there is also a significant opportunity to migrate customers who maintain legacy (non-SIP) PBXs and contact center systems.

SIP trunking is an excellent opportunity for businesses to slash operating costs, a particularly compelling idea in today’s unstable economic climate. There are a great many companies who have yet to make the switch to an Internet-based PBX. Whether the issue be cost, lack of expertise in making the migration or anything in between, the fact is there is a wide swath of small-to-medium businesses looking to leverage SIP trunks but unable to upgrade to an IP-PBX.

The solution is a SIP-capable Enterprise Session Border Controller (E-SBC) deployed at the network edge between a wide area IP network and the corporate LAN, securely passing SIP signaling and VoIP media streams to and from the corporate LAN. A media gateway resides on the corporate LAN and is connected to the legacy PBX or contact center via traditional T1/E1 trunk ports. The gateway passes the SIP trunk signaling and media from the E-SBC to the PBX by emulating traditional PSTN trunk services.

This setup will allow enterprises utilizing legacy PBX and contact center systems to easily and securely adopt SIP trunks as a replacement for traditional PSTN voice services.

It also presents a significant new market opportunity for SIP trunking providers and their resellers.

Important for success is proven interoperability. Security is in part dependent on truly interoperable solutions. The combined security features of the E-EBC with SIP-to-PBX trunk conversion capability of a media gateway that has demonstrated interoperability will enable a cost-effective, secure and reliable SIP trunk interface for customers. IT

Steven Johnson (News - Alert) is President of Ingate® Systems (

» Internet Telephony Magazine Table of Contents

Today @ TMC
Upcoming Events
ITEXPO West 2012
October 2- 5, 2012
The Austin Convention Center
Austin, Texas
The World's Premier Managed Services and Cloud Computing Event
Click for Dates and Locations
Mobility Tech Conference & Expo
October 3- 5, 2012
The Austin Convention Center
Austin, Texas
Cloud Communications Summit
October 3- 5, 2012
The Austin Convention Center
Austin, Texas