The External Accessory framework provides support for communicating with external hardware connected to an iOS-based device through the 30-pin dock connector or wirelessly using Bluetooth.
Application developers can use this conduit to integrate accessory-level features into their applications.
Communicating with an external accessory requires you to work closely with the accessory manufacturer to understand the services provided by that accessory. Manufacturers must build explicit support into their accessory hardware for communicating with iOS. As part of this support, an accessory must support at least one command protocol, which is a custom scheme for sending data back and forth between the accessory and an attached application. Apple does not maintain a registry of protocols; it is up to the manufacturer to decide which protocols to support and whether to use custom protocols or standard protocols supported by other manufacturers.
As part of your communication with the accessory manufacturer, you must find out what protocols a given accessory supports. To prevent namespace conflicts, protocol names are specified as reverse-DNS strings of the form com.apple.myProtocol. This allows each manufacturer to define as many protocols as needed to support their line of accessories.
