Chapter
8
Communications Device Class
This chapter describes the Communications Device Class (CDC) class and the associated
CDC subclass supported by μC/USB-Device. μC/USB-Device currently supports the Abstract
Control Model (ACM) subclass, which is especially used for serial emulation.
The CDC and the associated subclass implementation complies with the following
specifications:
■
Universal Serial Bus, Class Definitions for Communications Devices, Revision 1.2 ,
November 3 2010.
■
Universal Serial Bus, Communications, Subclass for PSTN Devices, revision 1.2 ,
February 9, 2007.
CDC includes various telecommunication and networking devices. Telecommunication
devices encompass analog modems, analog and digital telephones, ISDN terminal adapters,
etc. Networking devices contain, for example, ADSL and cable modems, Ethernet adapters
and hubs. CDC defines a framework to encapsulate existing communication services
standards, such as V.250 (for modems over telephone network) and Ethernet (for local area
network devices), using a USB link. A communication device is in charge of device
management, call management when needed and data transmission. CDC defines seven
major groups of devices. Each group belongs to a model of communication which may
include several subclasses. Each group of devices has its own specification besides the CDC
base class. The seven groups are:
■
Public Switched Telephone Network (PSTN), devices including voiceband modems,
telephones and serial emulation devices.
■
Integrated Services Digital Network (ISDN) devices, including terminal adaptors and
telephones.
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