1. APNS (Apple Push Notification Service)
- What It Is:
- Apple’s push notification platform for iOS, macOS, watchOS, and tvOS devices.
- How It Works:
- Developers send notifications via HTTP/2 requests to Apple’s APNS servers.
- Notifications are routed to the target device identified by a device token.
- Key Details:
- Requires authentication using a JWT-based token or certificate.
- Payload size is limited to 4 KB.
- Supports priority levels for immediate or deferred delivery.
2. FCM (Firebase Cloud Messaging)
- What It Is:
- Google’s push notification platform for Android devices and web apps.
- How It Works:
- Messages are sent via HTTP/2 or legacy protocols to Google’s FCM servers.
- FCM routes the notification to the appropriate devices or topics.
- Key Features:
- Supports both direct messages (device tokens) and topic-based fan-out.
- Payload size limit: 4 KB for notification messages, 100 KB for data messages.
- Can schedule notifications and manage retries automatically.
3. Web Push
- What It Is:
- A standard for sending push notifications to web browsers using the Web Push Protocol.
- How It Works:
- A service worker in the browser handles push messages.
- Requires a VAPID key pair for encryption and authentication.
- Messages are sent via HTTP to the browser vendor’s push service (e.g., Google for Chrome, Mozilla for Firefox).
- Key Details:
- Payloads are encrypted using public-key encryption.
- Supports both desktop and mobile browsers.