USB On-The-Go, normally abbreviated USB OTG, is a supplement [1] to the USB 2.0 specification.    

 

USB 1.0/1.1:  Those standards uses a master/slave architecture; a USB host acts as a master and a USB peripheral acts as a slave. Only the USB host can schedule the configuration and data transfers over the link. The USB peripherals cannot initiate data transfers, they only respond to instructions given by a host.

 

USB OTG changes that situation. Gadgets don't need to be pure peripherals; they can sometimes act as hosts. An example might be connecting a USB keyboard or printer to a handheld wireless device; or a USB printer that knows how to grab documents from certain peripherals and print them. The USB OTG compatible devices are able to initiate the session, control the connection and exchange Host/Peripheral roles between each other.

 

The USB OTG supplement does not preclude using a hub, however it describes role swapping only in the case of a one-to-one connection where two OTG devices are directly connected. If a standard hub is used, the USB OTG role-swap capabilities will end, locking one device as the Default-Host and the other as the Default-Peripheral until the hub is disconnected.

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