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WMCDC Abstract Control Model

Last Updated: 2/15/2017

There are two versions of the Abstract Control Model (ACM). The original version is defined in the USB Communication Device Class (CDC) specification. The USB Wireless Mobile Communication Device Class (WMCDC) specification contains an extended definition of the ACM. ACM collections that contain a fax/modem function should use the WMCDC definition of ACM rather than the original CDC ACM definition.

Interface collections that comply with the CDC specification are described in CDC Abstract Control Model.

Interface collections that comply with the WMCDC specification have the following properties.



Universal Serial Bus CDC Subclass Specification for Wireless Mobile Communication Devices, version 1.0, Section 6.2.

Class of the master interface

Communication Interface Class (0x02).

Subclass of the master interface

ACM (0x02).


If the collection uses an AT Command Set Protocol, the protocol value that is embedded in the compatible IDs is 0x01. If the collection uses one of the protocols that the WMCDC specification describes, the protocol value that is embedded in the compatible IDs is 0x2 through 0x06, or 0xFE.



Related interfaces

One data class interface that the union functional descriptor (UFD) references.

Hardware IDs


Compatible IDs


Special handling

The UFD might reference an audio interface collection that is enumerated independently of the ACM interface collection.

Interface collections must comply with the special descriptor and endpoint requirements that are specified in section 6.2 of the WMCDC specification. If the interface collection does not comply with the WMCDC requirements but the interface complies with CDC requirements, the USB generic parent driver will enumerate the interface collection and generic hardware IDs with CDC formats, as described in CDC Abstract Control Model.

The compatible IDs of this control model have a match in a Microsoft-supplied INF file. If the operating system does not find a match for one of the hardware IDs in a vendor-supplied INF file, the system automatically loads the native telephony application programming interface (TAPI) modem filter driver to manage the modem function and sets the appropriate TAPI registry settings, unless the protocol code is 0xFE. If the protocol code is 0xFE, the vendor must supply a device or class co-installer to correctly populate the TAPI registry settings.

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