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Back-to-Back User Agents Can Deliver the Goods for SIP

January 03, 2014

Software that automatically manipulates data is one of the most exciting computing applications for anyone who is a geek at heart. Having incoming data packets searched and adjusted on the fly before heading onto its next destination is just cool, as well as useful.


That’s exactly what a Back-to-Back User Agent (B2BUA) does for SIP. It accepts a SIP stream and potentially adjusts that stream before regenerating it and sending it along its way.

SIP is just a protocol. It has headers and a message body, and anything can be inside that message body. Usually SIP carries Session Description Protocol (SDP) in its message body, but technically it can be anything a business wants to put in the body. Like chess moves, for instance.

The trick is having a SIP-aware component that can do something with the incoming SIP data stream.

That’s where B2BUA comes in. SIP is usually about a User Agent Client (UAC) and a User Agent Server (UAS). A SIP phone (UAC) places a call, and that SIP message goes to a UAS for connecting with the other party. But a B2BUA can modify the SIP request before it forwards it onto another client.

This creates a lot of opportunities.

For instance, the B2BUA can potentially change every header along with the SIP URI and message body for a caller-ID masking service or a Call Admission Control (CAC) service. Or it could be used for deep-packet inspection, making sure the SIP stream is safe for the UAC.

It can be used for private IP address support. Instead of giving a public IP address to all users and servers, an organization can assign a private IP addresses that only make sense within the confines of an enterprise’s network, for instance.

A B2BUA can be used for policy enforcement, too, or topology hiding by masking the real identities of the users and services that live behind it. The IP address of an enterprise’s Session Manager could be removed from all outgoing SIP messages, for instance, being instead replaced with that of a Session Border Controller.

In fact, a Session Border Controller is basically a form of B2BUA that tackles security by letting in only some SIP streams and not others.

This implies an opportunity for SBCs, too. They currently are used for security, but what else could they do for a SIP stream? Are they offering the full range of control they can deliver as B2BUA? For SBC manufacturers, there is an opportunity to differentiate and provide added value by expanding the services they can offer with their SBC.

That’s because not just geeks enjoy automatic data manipulation. When it can save money or make a network more safe, management likes it, too.




Edited by Cassandra Tucker

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