iOS External Accessory Programming Topics

https://developer.apple.com/library/ios/featuredarticles/ExternalAccessoryPT/Introduction/Introduction.html

from https://developer.apple.com/hardwaredrivers/BluetoothDesignGuidelines.pdf
Third-party accessories can use the iPod Accessory Protocol (iAP) to access advanced features of iOS devices. One such feature is the ability to communicate securely with third-party iOS applications via the iOS External Accessory Framework. For information about the External Accessory Framework, see http://developer.apple.com/library/ios/#featuredarticles/ExternalAccessoryPT/Introduction/Introduction.html on the Apple iOS Developer site. To incorporate iAP into an accessory design, the accessory developer must be a member of the Apple MFi licensing program and integrate specific MFi hardware into the accessory. For further information about MFi, see developer.apple.com/programs/mfi.

iOS devices do not implement the Bluetooth RFCOMM (SPP) profile. from Bluegiga.
Instead Bluetooth accessories can use iAP profile to exchange data with iOS devices – iAP is RFCOMM based connection (similar to SPP) – It uses Apple proprietary iAP application protocol – Allows data exchange between Apps and the accessory • Audio, Human Interface (HID), PAN accessories and Bluetooth Smart devices are outside MFi program

Bluegiga:
iWRAP also implements 13 other Bluetooth profiles – Serial Port Profile – A2DP – Hands-Free Profile – Human Interface Device Profile – Health Device Profile – etc.
– Uses SPP to communicate with an Android App
– Uses iAP to communicate with an iOS App