[SR-Users] Integrating Push Notifications with iOS

Dear All, we are working on the integration of VoIP Push Notifications with iOS devices via Kamailio. From what we observe, the time window between receiving a VoIP APNS notification that wakes up the client app and the client app being sent back to the background by iOS is extremely narrow. It is around 1-2 seconds, with a (seemingly random) variance of say ~0.5s. So 1-2s is the time window available for getting the client app to properly REGISTER and to receive the INVITE back from Kamailio (using e.g. TSILO); otherwise the call is lost. (On Android, the equivalent time window extends to 10s or more.) Have others observed the same on iOS? We are using a client app that still uses the iOS 12 SDK (with Xcode10). Can we expect changes in that regard with iOS13/Xcode13? many thanks and cheers, Germán