USB MIDI v2_0.pdf"Universal Serial Bus Device Class Definition for MIDI Devices, Version 2.0"
As computers have become central components in many MIDI systems, USB has become the most widely used protocol for transporting MIDI data. With the introduction of MIDI 2.0, the USB Implementers Forum’s USB MIDI 2.0 working group, headed by members of the MIDI Manufacturers Association (MMA) and the Association of Musical Electronics Industry (AMEI), have updated the USB Class Definition for MIDI Devices. This spec defines how USB transports MIDI data.
The key to the updated spec is use of the new Universal MIDI Packet to support MIDI 2.0’s new functionality, while retaining backward compatibility with MIDI 1.0.
USB MIDI v2_0.pdf