From the SIP Trunking Experts

January 21, 2009

SIP Trunking As You Are

By Rich Tehrani CEO, Group Editor-in-Chief, TMC

Alan Percy, director of Market Development at AudioCodes, a leading provider of Voice over IP Telephony enabling technology, recently took some time to answer some very pointed questions about SIP Trunking, the market place for employing SIP Trunking with Legacy TDM PBXs, and AudioCodes’ roadmap for the future.

What is SIP Trunking?
Most businesses today have traditional TDM trunks that interface between their in-house telephone system and the public switched telephone network (PSTN).  SIP Trunking replaces those expensive TDM trunks with an IP-based service that uses SIP and the customer’s internet connectivity to perform the same function, connecting their telephone system to the public network. SIP Trunking fits a wide range of enterprise and SMB businesses and can significantly reduce costs.
What is “SIP Trunking As You Are”?
The strategy behind “SIP Trunking As You Are” is allowing business to enjoy the benefits of SIP Trunking with their existing TDM telephone system (PBX or Key Systems). This strategy allows the cost savings to be realized immediately and postpones/separates the decisions or costs associated with telephone system replacements.
What are the Business challenges in selling SIP Trunking to legacy TDM Telephone Systems?
A key challenge for both the business and their reseller is separating the sale of SIP trunking from any potential upgrades or replacement of the existing TDM telephone system. The objective is to avoid the protracted evaluation process required by the customer to select a new system, work out a migration plan and then execute a cut over. 
Another significant business challenge is the current economy. Most CFOs are not interested in large capital expenditures that would tie up cash or their lines of credit. The CFO wants to save money without spending money to get those savings. We think this strategy is a good fit for the current situation.
What are the Technical challenges when connecting SIP Trunking to legacy TDM Telephone Systems?
The biggest technical challenges that face organizations that want to move to SIP Trunking is interfacing with their existing TDM telephone system. The SIP trunks must be converted to a TDM format that is compatible with that specific PBX or key system, allowing the TDM circuits from the telephone system to be moved from the PSTN trunks to the SIP trunks with little or no adjustments to the telephone system.   Why spend more money on a PBX that you know is going to be replaced in a few years?
What equipment is needed for SIP Trunking with a TDM PBX?
Media gateways provide the interface between SIP Trunks and legacy TDM PBXs, converting from SIP signaling and VoIP packets to TDM formats that are compatible with the legacy TDM PBX. The AudioCodes Mediant 1000 is an excellent example of a modular and scalable media gateway that converts from SIP to a wide range of TDM protocols and physical interfaces. For very small analog-only installations, the AudioCodes MediaPack 11x line of analog media gateways is an alternative low-cost solution. 
Give some recommended configuration(s)?
For TDM phone systems that use T1/E1 digital trunk circuits, an AudioCodes Mediant 1000 should ordered with the same number of T1/E1 ports. Most small and medium business installations use from one to four T1/E1 circuits, which can be serviced by one Mediant 1000.
For phone systems that use analog trunk circuits, either a Mediant 1000 with analog FXO modules installed or a MediaPack MP-112/FXO (2 ports), MP-114/FXO (4 ports), or MP-118/FXO (8 ports) would be utilized, matching the number of ports on the media gateway with the analog trunk circuits on the PBX. For installations that require more than 8 analog ports, the Mediant 1000 with FXO modules should be used as it scales up to 24 FXO ports.
For more complex environments, the Mediant 1000 can also support a mix of digital and analog interfaces. (Check the Mediant 1000 User Manual for limitations) 
Can you give a few examples of certified SIP Trunking service providers?
AudioCodes has done extensive interoperability testing with a number of the leading SIP Trunking service providers including: Broadvox, Bandtel,, DeltaThree, Global Crossing, Level(3), SIPGate and a list of other too long to mention here. In addition to this list, we’ve also completed and secured SIP Connect certification which is managed by SIP Forum, an industry organization of service providers and equipment makers that have agreed to an interoperability standard.
What other important capabilities/features should be noted?
  • TDM Interoperability – allowing the installation of SIP Trunking while eliminating/minimizing the changes to the legacy TDM phone system
  • SIP Interoperability – certified with a large number of service providers, allowing a choice between a wide range of SIP Trunking offerings.
  • Voice Quality – delivering as good or better than PSTN voice quality
  • Fax Reliability – support for T.38 fax for reliable and efficient fax transport
  • Ease of installation and configuration – easy to use web configuration interface for both local and remote administration
  • Security – supporting industry standard security capabilities
  • Compact 1U package
  • Cost effective
What’s on the Roadmap?
When the time comes that the TDM phone systems is replaced, the Mediant media gateway continues to play an important role and can be re-purposed to provide connectivity to analog phones, fax machines, E911 calling or back-up TDM trunks. The Mediant 1000 can also be upgraded to a Multi-Service Business Gateway (MSBG), providing a secure interface between a new IP-PBX and the SIP Trunks. Other capabilities of the MSBG include data router, SIP-aware firewall and other security features.
 Where can we learn more?
We’ve hosted a number of web-based seminars on this and other related topics that can be viewed on demand at:  

Rich Tehrani is President and Group Editor-in-Chief of TMC. In addition, he is the Chairman of the world�s best-attended communications conference, INTERNET TELEPHONY Conference & EXPO (ITEXPO). He is also the author of his own communications and technology blog.

Edited by Tim Gray
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