What are the protocols supported in Iphone's External Accessory Framework

The External Accessory framework is for communication with custom hardware via the USB dock connector on the iPhone, or through Bluetooth. The device you are attempting to connect with must be part of the Made for iPod program, and must contain a chip that will decode the communication between the iPhone and the device.

The protocols referred to in the framework documentation are particular to each piece of hardware. The hardware manufacturer of, say, a game controller could set up a protocol for reading button presses or joystick movement. Any application which handled this protocol could then use that hardware accessory.

You will not be able to use the External Accessory framework to sync data via the USB connector. As Gerry suggests, you'll need to use WiFi or some other networking means to do so. In your previous question, Saurabh Sharan pointed out a hack for doing this through a tethered USB connection that the Cultured Code folks put together.