Mobile softphones that do not ring

See also

Sources

1. 1
   Android exempts Notification.CallStyle notifications from the POST_NOTIFICATIONS permission for apps that declare MANAGE_OWN_CALLS, implement ConnectionService and register with the telecom provider through registerPhoneAccount().

   Notification runtime permission · Section 'Exemptions' > 'Apps configured to self-manage phone calls' · Checked 2026-10-14
2. 2
   From Android 13 (API 33), posting non-exempt notifications requires the POST_NOTIFICATIONS runtime permission, and notifications are off by default for newly installed apps until the user grants it.

   Notification runtime permission · Sections 'Declare the permission' and 'Effects on newly-installed apps' · Checked 2026-10-14
3. 3
   For apps targeting Android 14 (API 34) or higher, the USE_FULL_SCREEN_INTENT permission used for full-screen incoming-call alerts on a locked phone is limited to calling and alarm apps; Google Play revokes the default grant for others, and users can turn the permission on and off.

   Behavior changes: Apps targeting Android 14 or higher · Section 'User experience' > 'Secure full-screen Intent notifications' · Checked 2026-10-14
4. 4
   Apple advises VoIP servers to set the apns-expiration header to 0 or a few seconds so that an incoming-call push is not delivered long after the call.

   Responding to VoIP Notifications from PushKit · Section 'Generate Push Notifications from Your Server' · Checked 2026-10-14
5. 5
   An apns-expiration value of 0 makes APNs attempt delivery once without storing the notification, while a nonzero value makes APNs store and retry the notification on a best-effort basis until that time.

   Sending notification requests to APNs · Section 'Send a POST request to APNs', header field apns-expiration · Checked 2026-10-14
6. 6
   Apple advises against sending further pushes to cancel or update a call after the initial VoIP push, because the app's existing network connection is faster and APNs may not deliver pushes reliably under poor network conditions.

   Responding to VoIP Notifications from PushKit · Section 'Generate Push Notifications from Your Server' · Checked 2026-10-14
7. 7
   APNs allows a VoIP notification payload of up to 5120 bytes, compared with 4096 bytes for a regular remote notification.

   Sending notification requests to APNs · Section 'Send a POST request to APNs', payload size · Checked 2026-10-14
8. 8
   An APNs request for a VoIP push uses the apns-push-type header value 'voip' and an apns-topic of the app's bundle ID with '.voip' appended.

   Sending notification requests to APNs · Section 'Send a POST request to APNs', header fields apns-push-type and apns-topic · Checked 2026-10-14
9. 9
   Cisco's push deployment guide states that if the push does not reach the mobile client within 13 seconds, the call to that client is dropped.

   Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Interactions and Restrictions (voice call delay) · Checked 2026-10-14
10. 10
    When a call is waiting on a push-woken mobile client and no ringback arrives within 5 seconds, Unified CM plays ringing to the caller itself.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Interactions and Restrictions (voice call delay) · Checked 2026-10-14
11. 11
    Cisco does not guarantee that the Android client's foreground service keeps it reachable in the background, notes that Android may terminate the app, and recommends Cisco Cloud Onboarding with FCM push for reliable calls.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Overview > Android Push Notification · Checked 2026-10-14
12. 12
    Unified CM supports VoIP push notifications for Jabber and Webex App on Android from release 12.5(1)SU3, and the Webex App on Android uses push for voice calls only.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Overview > Android Push Notification; Minimum Releases table · Checked 2026-10-14
13. 13
    From Unified CM 12.5(1)SU3 the push payload includes the active Unified CM node, so after a primary-node failure a woken mobile client registers directly to the active node instead of first trying its previous node.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Overview > Push Notification in case of Unified Communications Manager Failover · Checked 2026-10-14
14. 14
    Unified CM and IM and Presence push notifications require outbound TLS on port 443 from all cluster nodes to fos-a.wbx2.com, idbroker.webex.com and push.webexconnect.com, and Cisco says to add these domains to the firewall's SSL decryption exclusion list.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Prerequisites · Checked 2026-10-14
15. 15
    Cisco's guide states that push notifications became mandatory for Jabber and Webex App iOS clients on Unified CM in August 2020.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Overview > Apple Push Notification · Checked 2026-10-14
16. 16
    Cisco lists Unified CM 11.5(1)SU8 or 12.5(1)SU3, Expressway X12.6 for MRA, and Jabber 12.9 as minimum releases for push notifications to iOS 13 and later clients.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Minimum Releases and Feature Support (table) · Checked 2026-10-14
17. 17
    With LPNS, an iOS client on a configured Wi-Fi SSID (up to 10 in LocalPushSSIDList) keeps a WebSocket to Unified CM with keepalives every 120 seconds, and Unified CM falls back to APNs if local delivery fails.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Local Push Notification Service (LPNS) > How Local Push Connectivity Works; Configure Wi-Fi SSID · Checked 2026-10-14
18. 18
    Unified CM's Local Push Notification Service (LPNS), from release 14SU3, requires iOS 16.5 or later with Webex App 43.6 or Jabber 14.2. It carries voice calls only and is not supported on Android or for MRA users, who continue to use APNs.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Local Push Notification Service (LPNS) > Prerequisites; Interactions and Restrictions · Checked 2026-10-14
19. 19
    Cisco requires NAT and firewall devices to keep idle TCP connections from the cluster to the Push REST service open for at least 30 minutes, and states that a push is not retried on a new connection after an error.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Interactions and Restrictions · Checked 2026-10-14
20. 20
    Unified CM reaches background or suspended Jabber and Webex App clients on iOS and Android by sending a push through the Cisco Push REST service in the Cisco cloud to APNs or FCM, after which the client re-registers to Unified CM to accept the call.

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Push Notifications (On-Premises Deployments) > Overview · Checked 2026-10-14
21. 21
    Android documents forcing a device into Doze for testing with 'adb shell dumpsys deviceidle force-idle' and forcing an app into App Standby with 'adb shell am set-inactive <packageName> true'.

    Optimize for Doze and App Standby · Section 'Test with Doze and App Standby' · Checked 2026-10-14
22. 22
    Android's battery-optimization allowlist guidance rates exemption as not acceptable for calling apps that can use FCM high priority, and as acceptable for calling or enterprise VoIP apps that depend on another messaging service or whose core function Doze breaks.

    Optimize for Doze and App Standby · Section 'Acceptable use cases for exemption' (table) · Checked 2026-10-14
23. 23
    When a high-priority FCM message arrives during Doze or App Standby, Android delivers it and gives the app temporary network access and partial wake locks; Google says high priority should be used only for messages that produce a notification.

    Optimize for Doze and App Standby · Section on using FCM while the device is idle (high priority) · Checked 2026-10-14
24. 24
    In Android Doze, network access is suspended, wake locks are ignored, standard AlarmManager alarms are deferred to the next maintenance window, and JobScheduler and sync adapter work does not run.

    Optimize for Doze and App Standby · Section 'Doze restrictions' · Checked 2026-10-14
25. 25
    Google Play policy prohibits apps on Android 6.0 and above from directly requesting exemption from Doze and App Standby unless the app's core function is adversely affected.

    Optimize for Doze and App Standby · Section on battery optimization exemption, Google Play policy note · Checked 2026-10-14
26. 26
    FCM may downgrade high-priority messages to normal priority, or hand them to Google Play services for proxied delivery, when they do not result in user-visible notifications; it evaluates about seven days of behaviour separately for each app instance.

    Setting the priority of a message (Android) · Section on deprioritization of high priority messages · Checked 2026-10-14
27. 27
    Firebase Cloud Messaging delivers high-priority Android messages immediately and can wake a sleeping device for them, whereas normal-priority messages are delivered immediately only when the device is not sleeping.

    Setting the priority of a message (Android) · Section 'Normal priority' and 'High priority' · Checked 2026-10-14
28. 28
    Normal-priority FCM messages to an Android device in Doze wait for a maintenance window or for the device to wake.

    Optimize for Doze and App Standby · Section 'Using FCM to interact with your app while the device is idle' (normal priority) · Checked 2026-10-14
29. 29
    Firebase names a disabled notification permission as a common reason why an app's high-priority FCM messages produce no visible notification and so become candidates for deprioritization.

    Setting the priority of a message (Android) · Section on deprioritization of high priority messages · Checked 2026-10-14
30. 30
    Apps targeting Android 15 or higher cannot launch a phoneCall-type foreground service from a BOOT_COMPLETED broadcast receiver.

    Foreground service types · Section 'Phone call', restrictions · Checked 2026-10-14
31. 31
    Android's phoneCall foreground service type, used to continue an ongoing call through the ConnectionService APIs, requires the FOREGROUND_SERVICE_PHONE_CALL permission and either a MANAGE_OWN_CALLS declaration or the default-dialer role.

    Foreground service types · Section 'Phone call' · Checked 2026-10-14
32. 32
    The user setting that disables Android app hibernation is labelled 'Pause app activity if unused' in App info on Android 13 and later, 'Remove permissions and free up space' on Android 12, and 'Remove permissions if app isn't used' on Android 11.

    App hibernation · Section on asking the user to disable hibernation (settings table by OS version) · Checked 2026-10-14
33. 33
    When an app targeting Android 12 or higher is hibernated after months without use on Android 12+, its runtime permissions are reset and it receives no push notifications, including high-priority FCM messages, until the user interacts with it again.

    App hibernation · Section 'Effects of hibernation' · Checked 2026-10-14
34. 34
    Android does not hibernate apps installed in a work profile; if the same app is also in the personal profile, only the work-profile copy is exempt.

    App hibernation · Section 'System exemptions from hibernation' · Checked 2026-10-14
35. 35
    The device-maker-specific steps that Microsoft publishes for Teams suggest that OEM Android builds apply power management beyond AOSP Doze, App Standby and hibernation, so a softphone that rings correctly on a Pixel or emulator may still miss calls on some OEM devices.inferred

    Troubleshoot notifications in Microsoft Teams mobile apps · Android tab, device-specific sections · Checked 2026-10-14
36. 36
    A mobile softphone that is backgrounded or suspended rings only if every link succeeds: the call server sends a push, the push service (APNs or FCM) delivers it promptly, the OS lets the app run, and the app raises a call UI (CallKit on iOS, a call-style or full-screen notification on Android) within the server's call-delivery timeout. A missed call is therefore not by itself evidence of which link failed.inferred

    Push Notifications Deployment Guide: Push Notifications (On-Premises Deployments) · Overview and Interactions and Restrictions (13-second limit), read together with RFC 8599 Section 5.6.2, Apple PushKit Discussion and Android Doze FCM section · Checked 2026-10-14
37. 37
    Apple documents that after an app reports a VoIP push to CallKit the system shows the standard incoming-call interface unless an error occurs, for example when the user has enabled Do Not Disturb.

    pushRegistry(_:didReceiveIncomingPushWith:for:completion:) · Discussion section · Checked 2026-10-14
38. 38
    Apple states that an app built with the iOS 13 SDK or later that cannot support CallKit cannot use PushKit, and must use the User Notifications framework instead.

    Responding to VoIP Notifications from PushKit · Overview section · Checked 2026-10-14
39. 39
    On iOS 13 and later, if an app fails to report a VoIP push to CallKit the system terminates the app, and repeated failures may cause the system to stop delivering VoIP pushes to it.

    pushRegistry(_:didReceiveIncomingPushWith:for:completion:) · Discussion section, Important aside · Checked 2026-10-14
40. 40
    Apps linked against the iOS 13 SDK or later must report every PushKit VoIP push to CallKit by calling reportNewIncomingCall(with:update:completion:) on their CXProvider.

    pushRegistry(_:didReceiveIncomingPushWith:for:completion:) · Discussion section · Checked 2026-10-14
41. 41
    One NZ tells Android customers of its One Business with Webex service to turn off Android's unused-app setting for Webex, labelled in its title as 'pause app activity if unused'. One NZ says Android's idle pausing stops the app keeping calling features in sync and that the change slightly increases battery use.

    One Business with Webex | Turn off "pause app activity if unused" on Android devices · FAQ page body · Checked 2026-10-14
42. 42
    RFC 8599 defines SIP response 555 (Push Notification Service Not Supported), which a proxy sends only in response to a REGISTER to indicate that it does not support the requested push notification service type.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Sections 4.1.5 and 5.6.1.2; response code definition section · Checked 2026-10-14
43. 43
    Under RFC 8599 a user agent that wants push wake-ups adds the pn-provider, pn-param and pn-prid SIP URI parameters to the Contact header of its REGISTER request; pn-prid carries the push resource ID obtained from the PNS.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 4.1; Section 3 (push resource ID) · Checked 2026-10-14
44. 44
    RFC 8599 uses the pn-provider parameter to name the push notification service type, with values including apns, fcm and webpush.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 4.1.1 and the PNS-specific sections that define each pn-provider value · Checked 2026-10-14
45. 45
    RFC 8599 handles mid-dialog requests to a suspended user agent with the pn-purr parameter, which carries a proxy-issued registration reference that lets the proxy trigger a push for requests inside an existing dialog.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 6 (6.1.1, 6.2.1, 6.2.3) · Checked 2026-10-14
46. 46
    Under RFC 8599, when an initial INVITE or other dialog-creating or standalone request arrives for a user agent that cannot be reached, the proxy holds the request, sends a push, and forwards the request only after the user agent re-registers and receives a 2xx.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 5.6.2 · Checked 2026-10-14
47. 47
    Under RFC 8599, if the push request or the triggered re-registration fails, or the proxy's timer for the held request expires, the proxy rejects the held request with an error response such as 480.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 5.6.2 · Checked 2026-10-14
48. 48
    RFC 8599 has the proxy request a push at least 120 seconds before a registration binding expires if it has not received a refresh REGISTER, so that a suspended user agent can refresh its binding.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 5.5 · Checked 2026-10-14
49. 49
    RFC 8599 states that mobile operating systems may suspend an idle SIP user agent so that it cannot send REGISTER refreshes, receive incoming requests or keep connections alive, and it uses a push notification service (PNS) to wake the user agent.

    RFC 8599: Push Notification with the Session Initiation Protocol (SIP) · Section 1 (Introduction) · Checked 2026-10-14
50. 50
    Microsoft's Teams mobile troubleshooting tells Android users to enable all Teams app permissions, set Teams to 'Don't optimize' in battery optimization, and stop third-party cleaner apps such as Clean Master from blocking Teams notifications.

    Troubleshoot notifications in Microsoft Teams mobile apps · Android tab, steps for Android 6.0 and later and Android 6.0.1; third-party apps section · Checked 2026-10-14
51. 51
    Microsoft's Teams mobile troubleshooting gives device-maker-specific Android steps for Asus, Huawei, LeEco, Lenovo, OnePlus, OPPO, Samsung and Xiaomi, mostly enabling auto-start, protected-app status or battery-manager exemptions.

    Troubleshoot notifications in Microsoft Teams mobile apps · Android tab, device-specific sections · Checked 2026-10-14
52. 52
    Microsoft states that Teams call notifications are sent to the mobile app even when the user is active on the Teams desktop client.

    Troubleshoot notifications in Microsoft Teams mobile apps · Article introduction / notification behaviour note · Checked 2026-10-14
53. 53
    Webex documents that after an Android user unlocks the phone or SIM, incoming calls may be delayed for up to 60 seconds while services initialize; calls in that window do not appear and no push notifications are sent.

    Webex App | Answer a call · Section 'Known limitations (Android)', second bullet · Checked 2026-10-14
54. 54
    Webex documents that on Android, if the device is on a network but remains locked after a restart, Webex App does not receive incoming calls and they go to voicemail after several rings.

    Webex App | Answer a call · Section 'Known limitations (Android)', first bullet · Checked 2026-10-14
55. 55
    On iPhone and iPad, Webex App has an 'Incoming calls on this device' setting under Settings > Notifications > Calling with the values Banners and Sounds, Banners Only or Off, plus a Silence Rings toggle for Unified CM calling.

    Webex App | Manage notifications for incoming calls · iPhone and iPad tab · Checked 2026-10-14
56. 56
    Webex documents that after an iOS device restarts, Webex App cannot receive incoming calls until the device is unlocked.

    Webex App | Answer a call · Section 'Known Limitations' · Checked 2026-10-14
57. 57
    From Webex Mobile SDK 3.9.1, a developer registers its own REST endpoint for Webex Calling incoming-call notifications. Cisco sends the payload to that service, which pushes it through APNs or FCM so the app can receive calls in the foreground, in the background or after being killed.

    Supercharge Your App with Webex Mobile SDK 3.9.1 · Section on webhook-based call notifications · Checked 2026-10-14
58. 58
    Webex App incoming-call notification settings apply only to the device on which they are changed, so muting call notifications on desktop does not mute them on mobile.

    Webex App | Manage notifications for incoming calls · Article introduction (above the platform tabs) · Checked 2026-10-14
59. 59
    On 7 December 2021 Zoom recorded an incident in which the Zoom mobile app failed to ring for incoming Zoom Phone calls for a subset of North American users while the app was in the background; Zoom attributed it to one of its underlying providers and resolved it the same day.

    Issue with Zoom Mobile App not Ringing · Status updates 11:34 (Investigating), 13:09 (Identified) and 17:53 (Resolved) PST · Checked 2026-10-14
60. 60
    On 6 September 2024 Zoom recorded an incident of delayed push notifications to Android, Mac and Zoom Room devices that also affected Zoom Phone call logs and history; it was resolved the same evening.

    Issue with delayed push notifications · Incident impact text; updates 17:40 to 19:47 PDT · Checked 2026-10-14

Documents

Cite this page

WarmTransfer. (2026, October 14). Mobile softphones that do not ring. WarmTransfer. https://warmtransfer.net/knowledge/mobile-softphone-push-notifications

@misc{warmtransfer-mobile-softphone-push-notifications,
  title  = {Mobile softphones that do not ring},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/mobile-softphone-push-notifications},
  note   = {Verified 2026-10-14}
}