# How Do Push Notifications Work with PortSIP PBX?
### Understanding Push Notifications in VoIP Apps
A **Voice over Internet Protocol (VoIP)** app enables users to make and receive calls via the internet, bypassing traditional cellular services. However, maintaining a **persistent network connection** to receive incoming calls and data can lead to **high power consumption**. This is because the app constantly sends periodic messages to keep the connection alive, even when the app is not actively being used. This process causes frequent device wake-ups, which wastes energy, and can prevent the app from receiving calls when not running.
***
### The Power of Push Notifications for VoIP Apps
With **push notifications**, VoIP apps no longer need to remain active in the foreground or background to receive calls. When a call arrives, the server sends a push notification to the device, waking it up only when necessary. The user then receives an alert, providing them with an option to accept or reject the call.
#### Key Advantages of Push Notifications for VoIP Apps:
* **Energy Efficiency**: Push notifications wake the device only when necessary, conserving battery life.
* **High Priority**: VoIP push notifications are treated as high-priority and are delivered without delay.
* **Extended Data**: VoIP push notifications can carry more data than regular push notifications, making them more efficient for call management.
* **Automatic Relaunch**: If the app is not running, it will automatically relaunch when a VoIP push notification is received.
* **Background Processing**: Your app can process the push message, even if it’s operating in the background or has been forced out of memory.
***
### PortSIP PBX Push Notification Support
PortSIP PBX supports **mobile push notifications** for both **iOS** and **Android** from version **V9.0**. This feature ensures that all **PortSIP users** can benefit from efficient, timely, and reliable notifications for incoming VoIP calls, enhancing both user experience and energy efficiency.
***
### The Architecture of PortSIP PBX Push Notifications
The architecture below illustrates how **PortSIP PBX** delivers **push notifications** for incoming calls and messages when a mobile app is not running.
PortSIP PBX integrates with platform-native push services to ensure reliable call delivery while minimizing battery consumption on mobile devices.
***
### Call Flow for Sending Push Notifications
PortSIP PBX uses:
* **Apple Push Notification Service (APNs)** for iOS devices
* **Firebase Cloud Messaging (FCM)** for Android devices
The following sequence describes the end-to-end call flow for push notifications.
***
#### 1. Requesting a Device Token
When the mobile app is installed and launched for the first time, it requests a **device token** from:
* APNs (iOS)
* Google FCM (Android)
This token uniquely identifies the device and application instance.
***
#### 2. Receiving the Device Token
The push service returns a **device token** to the app.\
This token acts as the destination address for sending push notifications to the device.
***
#### 3. Registering with PortSIP PBX
The app registers with **PortSIP PBX** using a standard **SIP REGISTER** request.
To enable push notifications, the REGISTER request **must include an `X-Push` header**, which provides:
* Device platform (iOS / Android)
* Device token
* Application identifier
* Push notification preferences
This informs PortSIP PBX that the extension (for example, **extension 101**) supports push notifications.
***
#### 4. App Termination
The user **force-terminates** the app (swipes it away or the OS kills it).\
At this point:
* The app is no longer running
* It cannot receive SIP signaling directly
***
#### 5. Incoming Call
A caller dials **extension 101**.
If the SIP registration for extension 101 has not expired:
* PortSIP PBX attempts to send a SIP **INVITE** to the registered contact
* Since the app is terminated, the INVITE cannot be delivered
PortSIP PBX then triggers a **push notification** using the stored device token.
***
#### 6. Push Notification Delivery
APNs or FCM delivers the push notification to the user’s device.
The device:
* Wakes up
* Displays an incoming call alert to the user
***
#### 7. User Accepts the Call
When the user accepts the call:
* The operating system launches the VoIP app automatically
* The app performs a new SIP REGISTER to PortSIP PBX
***
#### 8. Call Establishment
After successful registration:
* PortSIP PBX sends a new SIP **INVITE** to the app’s updated contact address
* The app receives the INVITE and answers the call
* Media negotiation begins and the call is established
***
#### 9. Instant Messaging
The same push notification mechanism applies to **Instant Messaging (IM)**:
* Messages are delivered via push when the app is not running
* The app is launched to process and display the message
***
### Example `X-Push` Header in SIP REGISTER
Below is an example of the `X-Push` header included in a SIP REGISTER request:
```
X-Push:
device-os=ios;
device-uid=fe1b7bef1b4dc68dbfcd18143c8c06c122a25658c7f1d381c33fa626c9ed;
allow-call-push=false;
allow-message-push=false;
app-id=com.portsip.portsip-one
```
---
# Agent Instructions: Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.
Perform an HTTP GET request on the current page URL with the `ask` query parameter:
```
GET https://support.portsip.com/development-portsip/mobile-push-notifications/how-do-push-notifications-work-with-portsip-pbx.md?ask=
```
The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.
Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.