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Flexisip
A SIP phone system lives or dies on the unglamorous middle. Something has to route every call, know who is registered, wake phones that are asleep, and translate between networks that disagree. Flexisip is that middle, built as a modular server suite where you deploy only the pieces your service needs. The proxy routes calls and messages, relays media with ICE, STUN, and TURN support, and authenticates users by digest, TLS certificates, or OpenID Connect. Its push gateway speaks RFC 8599 to Apple and Google, so incoming calls ring phones whose app is closed, and it can lend that gift to an existing Asterisk or FreeSWITCH platform that lacks push of its own. The presence server tracks who is reachable and shares contact lists, the back-to-back user agent bridges SIP networks to PSTN gateways and trunks with codec transcoding and caller identity translation, and a registration event server notifies peer domains when users register. Instances cluster with load balancing for services that outgrow one box, the same suite shrinks onto a Raspberry Pi class intercom, and it has quietly powered the public linphone.org SIP service for over a decade. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.
Benefits
- Phones That Ring When Closed
- The push gateway wakes mobile apps through Apple and Google push for calls and messages, fixing the missed-call problem that makes self-hosted VoIP feel broken on phones.
- Deploy Only What You Need
- Proxy, presence, back-to-back user agent, and registration events are separate modules, so an intercom, a trunk bridge, and a national VoIP service each run a right-sized server.
- Bridges Old And New Telephony
- The B2BUA connects SIP accounts to PSTN gateways and operator trunks with transcoding, so modern apps can call ordinary phone numbers without replacing existing infrastructure.
- Proven At Public Scale
- The suite has powered the free linphone.org SIP service since 2011 and clusters with load balancing, which is a stronger resume than most telephony servers can show.
Features
- SIP Proxy Core
- Routes calls and messages for the whole service, relays media with ICE, STUN, and TURN, and anchors every other module's traffic.
- Push Notification Gateway
- RFC 8599 push to APNs and Firebase for incoming calls and texts, available standalone to add push to third-party SIP platforms.
- Presence Server
- Real-time availability status, reachable-contact identification in the user directory, and shared predefined contact lists for teams.
- B2BUA Trunking And Transcoding
- Connects SIP networks with PSTN gateways and SIP trunks, translating caller identity and transcoding media codecs and encryption between sides.
- Flexible Authentication
- Digest credentials, TLS client certificates, and OAuth with OpenID Connect secure user registration and calling on the proxy.
- Cluster And Embedded Modes
- Clustered deployment with high availability and a shared Redis-backed registrar, or a minimal footprint down to Raspberry Pi class hardware.