Вот оно:
/** Called any time the IceConnectionState changes. */
- (void)peerConnection:(RTCPeerConnection *)__unused peerConnection didChangeIceConnectionState:(RTCIceConnectionState)newState {
/*
* RTCIceConnectionStateNew,
* RTCIceConnectionStateChecking,
* RTCIceConnectionStateConnected,
* RTCIceConnectionStateCompleted,
* RTCIceConnectionStateFailed,
* RTCIceConnectionStateDisconnected,
* RTCIceConnectionStateClosed,
* RTCIceConnectionStateCount,
*/
}
, который реализован в RTCPeerConnectionDelegate
https://github.com/otalk/webrtc-ios/blob/master/include/RTCPeerConnectionDelegate.h#L59