OpenSIPS (SIP server / fork of OpenSER)
OpenSIPS is a high-performance SIP server forked from OpenSER in 2008 (the same project Kamailio also forked from). Like Kamailio, it is a Class 4 SIP signaling engine — routing, registration, dispatcher, fraud detection — not a PBX. The two projects have diverged significantly; pick based on the specific module set and ecosystem you need.
Kamailio vs OpenSIPS
Both forked from OpenSER (the original SIP Express Router) in 2008. Common heritage: same C-like config language, same module model, same SIP-only no-media philosophy.
Where they diverge today:
| Kamailio | OpenSIPS | |
|---|---|---|
| Default DB | db_text / db_mysql | db_mysql / db_postgres |
| Built-in B2BUA | mod_b2b_logic (lighter) | mod_b2b (richer, scenario-based XML) |
| Real-time stats | via mod_statistics | built-in event interface (E_*) |
| WebSocket | mod_websocket | mod_proto_ws / mod_proto_wss |
| OpenSIPS Control Panel UI | via Siremis (separate project) | OSC bundled |
| Documentation tone | RFC-style, terse | More tutorial-friendly |
Both are battle-tested at carrier scale. Pick based on team familiarity and specific module needs — the capability overlap is >80%.
DIDHub + OpenSIPS
DIDHub as an OpenSIPS dispatcher upstream — full DB-backed dispatcher table, uac_auth digest, route logic: OpenSIPS dispatcher tutorial.
Common usage patterns
- Carrier softswitch with high CPS demands (10K+ calls/sec).
- Multi-tenant hosted PBX front-end (with FreeSWITCH behind).
- SIP-WebRTC gateway for browser softphones.
- Fraud detection layer in front of legacy PBX.
Related terms
Kamailio (SIP server / softswitch)
Asterisk (open-source PBX framework)
FreeSWITCH
rtpengine (media proxy / relay)
Class 4 vs Class 5 Switches (Trunking vs PBX)
SBC (Session Border Controller)
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