USB communications device class

USB Communications Device Class ("CDC") (or together, "USB CDC") is a composite Universal Serial Bus device class. It is most commonly used for computer networking devices akin to a network card, providing an interface for transmitting Ethernet or ATM frames onto some physical media. It is also used for modems, serial ports, ISDN, fax machines, and telephony devices that perform regular voice calls. Devices of this class are also implemented in embedded systems such as mobile phones so that a phone may be used as a modem, fax or network port. The data interfaces are generally used to perform bulk data transfer. Microsoft Windows versions prior to Windows Vista do not work with the networking parts of the USB CDC, instead using Microsoft's own derivative named Microsoft RNDIS, a serialized version of the Microsoft NDIS (Network Driver Interface Specification). With a vendor-supplied INF file, Windows Vista works with USB CDC and USB WMCDC devices.