Editing USB communications device class (section)

{{Short description|USB device class}}
'''USB communications device class''' (or '''USB CDC''') is a composite [[Universal Serial Bus]] [[USB#Device_classes|device class]]. 

The communications device class is used for [[computer network]]ing devices akin to a [[network card]], providing an interface for transmitting [[Ethernet]] or [[Asynchronous Transfer Mode|ATM]] frames onto some physical media.  It is also used for [[modem]]s, [[ISDN]], [[fax]] machines, and [[telephony]] applications for performing regular voice calls.

[[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 [[RNDIS|Microsoft RNDIS]], a serialized version of the [[Network Driver Interface Specification|Microsoft NDIS]] (Network Driver Interface Specification).  With a vendor-supplied [[INF file]], Windows Vista works with USB CDC and USB WMCDC devices.<ref> [http://msdn.microsoft.com/en-us/library/ff538833.aspx Support for the Wireless Mobile Communication Device Class] </ref>

This class can be used for industrial equipment such as CNC machinery to allow upgrading from older [[RS-232]] serial controllers and robotics, since they can keep software compatibility. The device attaches to an RS-232 communications line and the operating system on the USB side makes the USB device appear as a traditional RS-232 port.  While chip manufacturers such as Prolific Technology, [[FTDI]], [[Microchip Technology|Microchip]], and [[Atmel]] manufacture USB chips and provide drivers that expose the chip as a virtual RS-232 device, the chips do not use USB CDC protocol and rather use their custom protocols, though there are some exceptions (PL2305<ref>[https://prolificusa.com/wp-content/uploads/2018/02/ds_pl2305I_v1.0.pdf PL-2305 USB to Printer Bridge Controller datasheet]</ref>).

Devices of this class are also implemented in [[embedded system]]s such as [[mobile phone]]s so that a phone may be used as a modem, fax or [[Port_(computer_networking)|network port]].  The data interfaces are generally used to perform bulk data transfer.