SIPIS

SIPIS (SIP Instance Server) is the component that keeps mobile VoIP users reachable when the app is closed or backgrounded. It maintains SIP registration on behalf of the device and triggers push delivery via APNs (iOS) or FCM (Android), so an incoming call wakes the app and rings reliably.

Operators can run SIPIS as a hosted service or self-host it. Self-hosting SIPIS gives full control over SIP credentials (no third-party storage), supports HIPAA-compliant architectures, and lowers latency by removing a hop from the push path. Push reliability is equivalent to the hosted option, since the actual delivery still flows through Apple and Google.

Regardless of where SIPIS runs, an APNs certificate (iOS) and FCM project credentials (Android) remain non-negotiable — Apple and Google control the final delivery leg. No self-hosted solution bypasses that.