OpenSBC Used for Lawful Intercept RFC

As someone who has been closely involved with the development of OpenSBC, the open source session border controller (OpenSBC is primarily developed and sponsored by Solegy), I always take pleasure (and not a little pride) when I find others who have been able to put it to good use.

The most recent example of this comes from the China Internet Network Information Center (CNNIC) - the Chinese equivalent to InterNIC, among other things.  The developers there have used OpenSBC as the foundation for a proof of concept demonstrating that lawful intercept can be successfully implemented in a session border controller, and their proposed architecture has been submitted to the IETF as an RFC.

Lawful Intercept is the process by which legally sanctioned authorities are able to access private communications through a wiretap.  This is  challenging in the VoIP world for many reasons, not the least of which is because audio payload often follows a different path than call control signals when packets are sent over the Internet.  In the United States, the Communications Assistance for Law Enforcement Act (CALEA) mandates that ITSP's and broadband service providers must be able to direct VoIP audio payload to a law enforcement agency, in realtime, upon receipt of a warrant.   

Typically, lawful intercept is performed in the core network using gear from vendors such as Narus or IP Fabric.  However, the RFC authors posit that the best place to perform this function for SIP traffic is at the session border controller.  Their motivation and intent are nicely stated in the introduction to the RFC:
One of the primary problems that service providers face when managing VoIP and multimedia calls is the separation of the signaling and media streams.  In other words it is quite possible that the two streams may take completely different paths through the network.  In addition, even when they do pass through the same device, it may not be aware of the relationship between the streams.  Some devices within the network are however specifically designed to understand and manage the separate signaling and media streams - session border controllers (SBC)[8].

SBC is a session-aware device that manages VoIP calls at the borders of an IP network.  Unlike most network devices, SBC are aware of the relationship between the two parts of a VoIP call: signaling and media.  Session Border Controllers handle both media and signaling, intercept can be performed in a completely undetectable manner.

SBCs usually sit between two service provider networks in a peering environment, or between an access network and a backbone network to provide service to residential and/or enterprise customers.  They typically are deployed at the border between two VoIP networks, and they offer an ideal location to implement a Lawful Intercept solution.

Whilst the detailed requirements for VoIP Lawful Interception may differ from one jurisdiction to another, the general requirements are the same.  The LI system must provide transparent interception of specified traffic only and the subject must not be aware of the intercept.  The service provided to other users must not be affected during interception.

As part of the effort in developing a broadband VoIP lawful interception architecture, we implemented a prototype and conducted evaluation experiments on the prototype system.  In this document, we first describe the prototype solutions and then report experimental results.  We hope that this document can provide useful information to those interested in the subject.

I couldn't agree more.  Unlike most other Internet traffic, SIP is well suited to this approach because most service providers funnel SIP messages through a border proxy of some sort for access control or billing purposes.  As a result, with the exception of P2PSIP, there is ample opportunity to identify sessions of interest and redirect the audio packets through a collection point.  

According to the RFC authors, the OpenSBC extensions and media capture module used in their solution will be contributed back to the open source community in the near future. 

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