SIP/Element: Unifying Telephony and Modern Communication (matrix-conf-2025)

Our project's main goal was to fill a gap by developing a telephony bridge that natively integrates XiVO enterprise telephony (based on SIP) within the alternative and open-source Matrix/Element ecosystem. Our focus with this bridge is to offer a credible and high-performing alternative to dominant proprietary solutions, such as Teams and its "Telephony System" licenses. XiVO SIP bridge project presented a significant development challenge, underscoring its disruptive and creative nature. This wasn't a simple assembly of existing technologies, but an engineering effort to bridge two fundamentally different protocols: WebRTC used by Matrix ecosystem and SIP from the IP telephony world. This bridge (built as a Synapse module for now) allows Element to integrate enterprise telephony capabilities provided by XiVO, open source IPBX using Asterisk. The integration approach between XiVO telephony and the Matrix protocol involved designing specific gateways and APIs for interoperability of identities (XiVO user vs. Matrix user, i.e., phone number vs. mxID) and telephony features (answer, hang up, hold, etc.) directly within the Element Web interface. The impacts, and outcomes of this successful bridge project are significant. It allows a substantial reduction in communication costs for businesses by eliminating proprietary telephony licenses, all within a single, open-source unified communication tool. It also creates value for the French and European open-source ecosystems. In short, the XiVO/Element bridge is not a mere improvement on existing solutions but a disruptive proposal that creates a "bridge" between the world of traditional telephony and modern unified communications. It, nevertheless, required solving complex problems: - How do you reconcile different protocols and semantics? The SIP protocol manages specific states and signals (e.g., INVITE for ringing, HOLD for putting a call on hold) that have no direct equivalent in the Matrix protocol. The difficulty lies in designing a mechanism capable of interpreting these SIP events, translating them into relevant Matrix events, and vice versa, to maintain a consistent user experience. - The bridge must be able to robustly track the state of these sessions and ensure that actions performed on one side (for example, rejecting a call in the web interface) are correctly executed and reflected on the XiVO PBX in SIP. A failure in this IPBX/Matrix synchronization could lead to inconsistencies (e.g., a call that still appears active on one side even though it has ended on the other). The idea is to use this presentation to share our progress on this bridge, its integration into our soft-fork of Element (xivo-connect) with a supporting demo, and our expectations to integrate it into Tchap (French gov soft-fork of Element). We also want to share our successes and ideas for the future to benefit the entire Matrix community. Licensed to the public under https://creativecommons.org/licenses/by-sa/4.0/ about this event: https://cfp.2025.matrix.org/matrix-conf-2025/talk/CYXHGK/