iOS 13 PushKit VoIP restrictions breaking SIP VoIP apps

Hi,


We are a fairly large company providing smartphone and desktop applications for VoIP/UC together with PBX systems, on-premise as well as clourd offerings. All our app are talking to the telephony servers over SIP.

Up unitl now, our flow on iOS was:

  1. Receive PushKit VoIP notification
  2. REGISTER towards telephony server
  3. Receive INVITE
  4. reportIncomingCall


With the changes enforced and outlined in https://developer.apple.com/videos/play/wwdc2019/707/, the whole SIP concept will break.

We are now forced to report an incoming call so early that the user might accept the call before the REGISTER has completed and an INVITE has been received which will lead to a pretty bad user experience.

Even worse, we will report an incoming call even if there is no actual call. This might happen as the call has already been canceled on the remote end and we won't get an INVITE. Or if the registration fails due to network issues that prevents us from reaching the telephony server.


How does Apple expect us to deal with these situations?

It's not possible to perform the whole REGISTER/INVITE stuff "in the same run loop as pushRegistry:didReceiveIncomingPushWithPayload:forType:[withCompletionHandler:] without delay."


I'm not sure what our support and sales guys will do when they receive negative customer feedback with the changed implementation. Maybe tell existing and new customers to use Android smartphones instead of iPhones...


There has to be at least some way of delaying the reportIncomingCall so that an application can check against the telephony server if there is a call and report if there is none to avoid punishment for not reporting the call.

Accepted Reply

A lot of different issues have been raised in this thread, so I've loosely summarized them to the following 4 questions issues:



1) Reporting a call immediately does not work with the SIP register-invite flow


On iOS 13, there are cases where you will need to initiate a CallKit call that you previously would have silently ignored. However, in practice, this should not be the common case, particularly for truly “non-existent" calls, since that would mean you had been notifying the user of calls that did not exist.


The more common cases here are calls that have either already ended (because the caller hung up) or can't be completed (because network conditions prevent the call from connecting). While calls will be created for both of these cases, there are few different techniques that you can use to mitigate any disruptions:


While you must report an incoming call immediately, you are still free to decide the call has failed and tell the system later, asynchronously. To do this, call reportCallWithUUID:endedAtDate:reason:. This will tear down the incoming call UI even if the user has not answered the call.


If the user is particularly fast at tapping the accept call button, or if the network conditions are poor or there is otherwise a lot of latency, then you should simply wait until the necessary handshakes are complete before calling fulfill on the CXAnswerCallAction. To the user, it simply appears that the call is taking some time to connect, which is a common experience even with standard phone calls.


Note that the system takes a few seconds for the incoming call UI to animate in, during which the app has the opportunity to complete this handshake, so this will only have a user-visible impact if it takes a significant time for the handshake to complete.


At any time, you can asynchronously update the UI with the reportCallWithUUID:updated: API. That means that if you cannot put the caller ID info in the push payload, you can simply choose to present dummy information (like "Connecting Call..." for the caller name) and update it asynchronously once they get the real information from your server.


2) Sending a push to cancel an incoming call


While your app currently has an active call (ringing or answered), your app is not required to create additional calls for VoIP pushes received during this call. This is intended to be used to support advanced functionality like dynamic call priority, but it could also be used to cancel an incoming call.


Having said that, this is not an approach I would recommend or rely upon. The reality is that as soon as your app receives it's PushKit notification it should be connecting to your server, so unless network conditions are very poor, you should be able to communicate to your client through that connection faster than PushKit. More to the point, if network conditions mean that you can't connect to your server, then trying to handle this with another push isn't a great idea either, since poor connectivity (and timing generally) opens the door to edge cases you'd want to avoid - for example, a client receiving ONLY the cancelation and not the original call notification.


As a side note here, keep in mind that as part of adapting to the new requirements you'll want to make sure the VoIP notification has a short or zero "apns-expiration" to prevent newly available devices from being notified of out-of-date calls. This will also minimize the cancelation issue, since a “newly available device" (for example, a phone that was just powered on) will ONLY receive notifications about calls that are occurring at that particular instant.


3) Block-lists/Do Not Disturb


CallKit respects the system Do Not Disturb setting, so most apps will not have to worry about system-level Do Not Disturb functionality. If your app has it's own blocking/do not disturb system built in, you can also maintain that list server-side and not send pushes to the blocked devices. If you absolutely need to do "local" call blocking, then you can report a call and then end it. The call will be briefly visible to the user, but you can also configure the source of the call to communicate what's going on ("Blocked Call...").


4) Using VoIP pushes to trigger syncs or other non-VoIP use cases


VoIP pushes were always intended to specifically support call notifications and nothing else. The good news here is that using Notification Service Extension is the best substitute for most of the functionality that you previously handled with PushKit:


https://developer.apple.com/documentation/usernotifications/unnotificationserviceextension


A few examples:

  • For general messaging, you can connect to your server in the extension delegate, download any missed messages, and then update the notification content as appropriate.
  • The same approach can be used to tell the user about calls missed while the device was offline and/or pending voicemails.
  • For non-user facing functionality, like data synchronization or other app maintenance, I would recommend checking out the new BackgroundTasks framework:


https://developer.apple.com/documentation/backgroundtasks


Kevin Elliott

Developer Technical Support

Core OS/Hardware

Replies

If I build my App using Xcode10, it works well on iOS13. But if I build it by Xcode11, call failed alert will pop up.

I write a simple demo only contain PushKit code. This bug still happens.

I submited a feedback on Sep 2, but still didn't get any response.

Also I submit a DTS recently and still wait for the solution.

Does any other developers experience the same "Call Failed" alert?

Hi KevinE,



So, my understanding is:

1) For iOS 13, Apple still support VOIP push.

2) App integrated with the PushKit must calls the [CXProvider reportNewIncomingCallWithUUID:] in the didReceiveIncomingPushWithPayload: forType: method. Right?

BTW, my device (iPhoneXs Max, 13.0) can not receive any VOIP push on 11th. Oct in China. Do the VOIP push service is pending for some reason?

Hi all,


in our Voip app we have a case for which we have so far no solution and which has not been treated here.

We get ping-pushes every hour from the Voip server, which we have to answer in the background with a "register" without a user action. If there is no answer, the Voip account is set to offline and callers receive the busy tone. So far, we could easily send the ping push as a Voip Push. With the change now this is no longer possible.

Normal pushes are out of the question, because when the app is terminated, we can not automatically send the "register" in the background without user action with normal push notifications.

This means for us that no more incoming calls arrive when the app has been terminated, which is not acceptable.


Has anyone an Idea how to solve the ping-push problem in compliance with the new rules?


Thanks

I'm facing the same issue: if a cellular call is in progress, it fails when a VoIP notification arrives (displaying alert "Call failed") and the delegate method pushRegistry:didReceiveIncomingPushWithPayload:forType:[withCompletionHandler:] is not called.

There is another problem here.


AFAIK Apple won't approvel any application with Callkit in Chinese App Store as Chinese gov required, which means I can not use PushKit neither in Chinese App Store? These seems no way to use PushKit avoiding CallKit, am I corrected?

The same to me. The callback is not called. But DTS think it's probably our Callkit code blindy do "action.fulfill()".

func provider(_ provider: CXProvider, perform action: CXStartCallAction) {
    action.fulfill()
}

I change my code, but still have the problem.

Did you ever find a solution to your problem with "Call Failed"? I'm experiencing this issue too.

It looks like the "call failed" issue has been fixed with iOS 13.2.

I do agree 100% with this.


There could be multiple reasons to reject the Incoming Call from SipStack when INVITE is recieved.

Showing GHOST incoming call in Apple CALLKIT UI, while call gets rejected from Sip Stack , as SDP in INVITE does not have attributes that could match.

Hi Ptank,
I Dont know "how to handle call cancellation scenario?"
This post explained Voip and sip call all kinds of details : https://blog.mirrorfly.com/sip-protocol-with-webrtc-application/

I hope this post will helps to you.

Hi,

Firstly thank you for this information,

Secondly, You mentioned not needing to report new calls when we already have a ringing or active call.
What happens if we get two voip pushes at the same time, for example from two different callers.
From our testings, (Xcode 10, not 11 yet) when the second push arrives, we still do not have an active or ringing call reported from the first push. Do we need to still report a call for the second push? Doing that resulted in both calls reporting succesfully and eventually failing after the user sometimes needing to respond to two incoming call screens one after the other.
Will this behaviour be rectified when building with xcode11?


Best Regards

Kevin, just so you are aware, this is a huge FAIL for those of us working in the enterprise domain. Losing the ability to activate an app in the background for data purposes is a dealbreaker for many apps.

I have the same problem with my xmpp app, do you found any alternative way to handle it?

Hello, According to this announcement https://developer.apple.com/news/, can you confirm that we have until June 30 to complete the changes related to callkit? Thank you

I'm having similar issue. Did it worked for you ??