Enterprise SBCs: Why They're So Important
Session border controllers provide security, but their value to the enterprise goes much deeper--they can help you unify dial plans and tie together legacy elements.
Enterprise Session Border Controllers or E-SBCs provide a simple and manageable way to deliver strong security boundaries between enterprises and carriers when deploying SIP trunks. E-SBCs can also provide substantial benefits well beyond security, especially when bundled with Session Management. Session Management describes an evolving set of capabilities that provide E-SBCs with, among other things, the ability to manipulate dial plans, allowing organizations to deploy SIP trunks without the need for wholesale overhaul of their dial plan. In addition, Session Management within E-SBCs offers the ability to address SIP interoperability challenges by providing administrators with tools to modify and normalize SIP traffic between vendors' systems.
With Session Management, enterprises can consolidate their dial plan and eliminate complex routing configurations across multiple PBXs and platforms. This ultimately sets the stage for the adoption and migration to large scale carrier-provided SIP trunks for carrying voice and other media including video.
We'll explore a few of the benefits and tricks in more detail in the following article.
Normalizing Dial Plans
Normalizing a dial plan can be complex and the options limited when the enterprise is attempting to connect and integrate legacy PBXs. Many legacy PBXs have limited support for how digits can be manipulated, or may simply limit the number of digits allowed. Likewise, many legacy carrier trunks have been configured to accommodate these limitations by passing a subset of the digits dialed when forwarding a call to an enterprise PBX.
In addition to providing a security boundary between your enterprise IP Telephony deployment and carrier networks, an E-SBC can also be used to normalize your dial plan as well as manage call delivery to multiple destinations through Session Management. In a centralized deployment model, the E-SBC can manipulate digits from multiple sources and provide a relatively simple and low-risk option for transition to an enterprise dial plan.
Consider a case in which you are configuring the E-SBC to normalize calls routed to a legacy PBX via a SIP trunk. In this case you could deploy an e.164 dial plan at the enterprise level while preserving a 4- or 5-digit dial plan for legacy PBX deployments. You could deploy the E-SBC to terminate a SIP trunk that is replacing a legacy PRI: In this case your legacy PBX may have been configured with a 5-digit dial plan and your previous provider was only sending you the last 5 digits of the called number. In the new SIP configuration, you could have the SIP provider send you the full e.164 number (11 digits in the case of North America Numbering Plan, NANP) and have the E-SBC strip the first 6 digits when it forwards calls to the legacy PBX. As a result, you remove the need for any reconfiguration of the legacy PBX while positioning yourself to integrate and transition to a new IP PBX or Rich Media solution like Microsoft Lync. By using this approach you align the enterprise to a common dial plan, and by using an e.164 dial plan you guarantee against any number overlap.
Next page: Illustrating the Scenario