create Ring to SIP gateway

Issue generated from Tuleap's migration script. Originally submitted by: Daniel Pocock (pocock)

Create gateway from Ring to SIP (e.g. an SBC / B2BUA), the reConServer project based on librecon from reSIProcate may provide a useful framework for this.

reSIProcate developers are looking at adapting librecon to work with libjingle:

https://www.resiprocate.org/bugzilla/show\_bug.cgi?id=93

This would be useful for bridging Ring calls to corporate PBXes and WebRTC.