Controlling media of ongoing calls with just a SIP Proxy

SIP proxies, by definition, lack the ability to do any media handling, due to the fact that they only stand in the path of call signalling, but not call media (as opposed to a B2B media server, which behaves as an endpoint for both media and signalling). So, how do you keep your OpenSPIS as a performant SIP proxy, but also enhance your SIP service with extra media capabilities? Starting version 3.1, OpenSIPS provides the means of controlling and changing the RTP streams of the ongoing calls without altering the signalling path of the call (i.e. without transferring the call to a B2B media server), as the calls should be easily resumed to its initial state. A set of examples where manipulating media in an ongoing call can be useful, while preserving its signalling path, are: inject an audio/video announcement playback music on hold files fork media for call recording, or for call listening inject media for call whispering temporary barge in an ongoing call All these features, and many others can be implemented by simply mixing the participants of multiple calls. This presentation describes how all these features can be implemented in OpenSIPS 3.1 using the new Media Exchange module, without changing the SIP signalling path, but only by exchanging SDP bodies between different SIP sessions.