USB Communication Device Class

Base Class 02h，通訊裝置包括電話、PSTN/DSL/Cable 數據機、ISDN、Ethernet/ATM/無線/行動網路。

Class Code	SubClass	說明
02h 01h	Direct Line Control Model	[USBPSTN1.2]
02h 02h 00h	Abstract Control Model (CDC-ACM)	No Class Specified Protocol [USBPSTN1.2]
02h 02h 01h		AT commands [V250] [USBPSTN1.2]
02h 03h	Telephone Control Model	[USBPSTN1.2]
02h 04h	Multi-Channel Control Model	[USBISDN1.2]
02h 05h	CAPI Control Model	[USBISDN1.2]
02h 06h	Ethernet Networking Control Model	[USBECM1.2]
02h 07h	ATM Networking Control Model	[USBATM1.2]
02h 08h	Wireless Handset Control Model	[USBWMC1.1]
02h 09h	Device Management	[USBWMC1.1]
02h 0Ah	Mobile Direct Line Model	[USBWMC1.1]
02h 0Bh	OBEX	[USBWMC1.1]
02h 0Ch	Ethernet Emulation Model	[USBEEM1.0]
02h 0Dh	Network Control Model	[USBNCM1.0]

一個 CDC 裝置必須支援兩個 Interface，一個描述所支援的功能，另一個描述資料傳輸的通道，透過 IAD (Interface Association Descriptor) 將兩者宣告屬於同一個 function。

RS232 over USB

Ethernet over USB：透過 USB 傳送 Ethernet frames，達到這的目的協定有 Microsoft 的 Remote Network Driver Interface Specification (RNDIS)、CDC Ethernet Control Model (ECM)、CDC Ethernet Emulation Model (EEM)、和 CDC Network Control Model (NCM)。

ECM 用在 USB full speed。

EEM is intended for use in communicating with devices, using Ethernet frames as the next layer of trans- port. It is not intended for use with routing or Internet connectivity devices, although this use is not pro- hibited.

NCM 改良 ECM 1.2 支援更高 data rates：單一 USB 傳送可送多個 Ethernet frames，並可指定偏好位置減少處理 overhead。NCM 定義兩種 encapsulating datagrams，一種長度可達 64KiB 可放 40 Ethernet frames，另一種達 4GiB 支援 High Speed 和 SuperSpeed data rates。一個 NCM function 包含一個 NCM Communications Interface 和一個 NCM Data Interface。NCM Communications Interface 用來設定和管理 the networking function。NCM Data Interface 使用定義的 endpoints 來傳送 data。

參考

1. http://pollos-blog.blogspot.com/2014/10/rs232-over-usb.html
2. https://en.wikipedia.org/wiki/Ethernet_over_USB
3. https://www.usb.org/document-library/network-control-model-devices-specification-v10-and-errata-and-adopters-agreement
   

• 比較：Video、MTP 傳送特定應用協定