# AccessoryTransportAppExtension A protocol for an extension that transmits data to an accessory you develop. ``` protocol AccessoryTransportAppExtension : AppExtension ``` ## Overview Implement this protocol in an extension with an `EXExtensionPointIdentifier` value of `com.apple.accessory-transport-extension` to relay data to your accessory. The extension supports sharing Wi-Fi networks and forwarding iOS system notifications. > Important: The system requires your app extension to have the entitlement to use this protocol. ## Wi-Fi network sharing Use this extension with to share a Wi-Fi network with your accessory. The system calls your extension’s [`accept(sessionRequest:)`](/documentation/AccessoryTransportExtension/AccessoryTransportAppExtension/accept(sessionRequest:)) method when it needs to establish a transport session for Wi-Fi sharing. In your extension’s target properties, specify the extension point identifier: ```xml EXAppExtensionAttributes EXExtensionPointIdentifier com.apple.accessory-transport-extension ``` In your extension’s Swift code, implement the protocol and provide an event handler: ```swift @main struct TransportExtension: AccessoryTransportAppExtension { func accept(sessionRequest: AccessoryTransportSession.Request) -> AccessoryTransportSession.Request.Decision { return sessionRequest.accept { MyTransportEventHandler(session: sessionRequest.session) } } } class MyTransportEventHandler: AccessoryTransportSession.EventHandler { func invalidationHandler(error: AccessoryTransportSession.Error?) { // Clean up when the session ends. } } ``` After accepting a session, your extension connects directly to the accessory using and delivers Wi-Fi network data using . ## Notification forwarding For notification forwarding, set up your extension the same way as for Wi-Fi network sharing. The system invokes your extension to relay encrypted notification data from your app’s [`AccessoryDataProvider`](/documentation/AccessoryTransportExtension/AccessoryDataProvider) extension to your accessory. Implement [`dataEventHandler(event:)`](/documentation/AccessoryTransportExtension/AccessoryTransportSession/EventHandler/dataEventHandler(event:)) in your event handler to receive and transmit data: ```swift class MyTransportEventHandler: AccessoryTransportSession.EventHandler { func dataEventHandler(event: AccessoryTransportSession.DataEvent) { switch event { case .ciphertext(let data, let featureID): // Transmit encrypted notification data to accessory over Bluetooth. sendToAccessory(data) case .plaintext(let data, let featureID): // Transmit plaintext data to accessory. sendToAccessory(data) } } func invalidationHandler(error: AccessoryTransportSession.Error?) { // Clean up when the session ends. } } ``` The system encrypts data using keys through your app’s [`AccessoryTransportSecurity`](/documentation/AccessoryTransportExtension/AccessoryTransportSecurity) (ATS) extension and then delivers the encrypted data as `ciphertext` to your handler. Your extension transmits the encrypted data to the accessory, which decrypts the data using shared encryption keys. > Note: > Call ``doc://com.apple.AccessoryTransportExtension/documentation/AccessoryTransportExtension/AccessoryTransportSession/cancel(error:)`` on the session if your extension encounters an error that requires terminating the session. ## Topics ### Accepting session requests [`accept(sessionRequest:)`](/documentation/AccessoryTransportExtension/AccessoryTransportAppExtension/accept(sessionRequest:)) Handles a new session request for the accessory. [`Decision`](/documentation/AccessoryTransportExtension/AccessoryTransportSession/Request/Decision) An opaque type returned from the incoming session handler of an event listener. ### Handling session events [`EventHandler`](/documentation/AccessoryTransportExtension/AccessoryTransportSession/EventHandler) A protocol that defines methods for handling transport session events. [`DataEvent`](/documentation/AccessoryTransportExtension/AccessoryTransportSession/DataEvent) An enumeration of data events that the transport extension receives. ### Managing sessions [`AccessoryTransportSession`](/documentation/AccessoryTransportExtension/AccessoryTransportSession) A class that manages a transport session between the extension and the system. ## Relationships ### Inherits From [`AppExtension`](/documentation/ExtensionFoundation/AppExtension) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)