In iOS9 apple deprecated setKeepAliveTimeout and recommend UIRemoteNotification with VOIP Type available in PushKit for VOIP calling. Ok I can imagine that I will write server application for sending these notification.
1) But what-if i need periodically re-register to proxy server.
2) And what about sip-proxy? Does it mean, that all sip-proxies will need extension for sending these notifications to iOS Devices?
I founded answers to these questions here: https://forums.developer.apple.com/thread/49363
tl;dr 1) re-registering is not in iOS 10 no longer supported 2) generic sip-proxy app is also not available in iOS 10