The article originally appeared in the Jan./Feb. edition of INTERNET TELEPHONY.
The key to any successful SIP deployment is, and has always been, interoperability. It was a key issue driving the development of SIP: When the Internet Engineering Task Force first introduced SIP one goal was to create a streamlined protocol that would pave the way to seamless interoperability.
Vendors know this, and have been redesigning their solutions to incorporate all of the legacy PBX (News - Alert) functionality in a PBX built on a full SIP implementation.
Why, then, is interoperability still an important part of the VoIP network design?
When implementing SIP trunking, interoperability must work seamlessly between two sources: the IP PBX and the SIP trunking service provider. Even though the IP PBX may be a full SIP implementation, there can still be a mismatch between that PBX and the SIP trunking service.
The SIP standard, like many Internet protocols, is written to give the industry wide latitude in how various functions are performed. While this provides maximum opportunity for innovation, it also means that each vendor may choose how each function works.
And there is no guarantee that both the IP PBX vendor and the SIP trunking service provider will have chosen the same methods. Without complete commonality of the methods chosen, the SIP trunking implementation will be difficult or impossible to complete, which is one of the roles that the enterprise session border controller can play.
An E-SBC is a tool that can make an IP PBX compatible with whatever SIP trunking service may be on the other side. Basically, the E-SBC can terminate the call from one side and reinitiate the call with modified header information to insure that it will be recognized by the other party.
By resolving these interoperability issues, E-SBCs simplify installations – so much so that deployments can take just minutes rather than hours or even days.
One other interoperability requirement occurs when another device requires encryption of either the signaling, media or both. In this situation the E-SBC can add the encryption necessary to interoperate with the other device.
We will explore this aspect of interoperability in a future article.
With a good E-SBC not only can the customer count on seamless integration with the SIP trunking service provider, and a good source of diagnostics as we discussed last month. But in addition, and equally important, is security, which the E-SBC provides as an integral part of its functionality.
Edited by Braden Becker