Then the packet is checked with a 16-bit CRC field. These two speeds make it possible to have low-cost USB peripherals like mice or joysticks without having a shielded USB cable. The fields Vendor ID and Product ID play the key role in the enumeration of the device. The descriptor also informs the host as to the number of configurations of the device. The device descripter also contains specification release, class information, device protocol, max packet size for EP0, and the number of configurations.
Endpoints behave as a group of FIFOs.
Enumeration takes place anytime the bus is started or a device is plugged into or unplugged from the bus. These packets inform the sender of the data as to the condition of the received data packet. Device's endpoint is incapable of receiving or sending data. This requires host intervention. Hubs are responsible for the removal and addition of USB devices.