USB PPP
PPP (Point-to-Point Protocol) is one of the most fundamental protocols in networking. It is a data link layer protocol designed for simple links to transmit data packets between peer units. These links provide full-duplex operation and sequential packet delivery. PPP offers a common solution for simple connections based on various hosts, bridges, and routers.
The iot_usbh_modem component implements the complete process of USB host PPP dial-up. It supports connecting 4G Cat.1/4 modules via USB interface to achieve PPP dial-up internet access. It also supports sharing internet connection to other devices through Wi-Fi softAP hotspot.
- Features:
Quick start
Hot-plug support
Dual interface support for Modem+AT (module dependent)
PPP standard protocol support (supported by most 4G modules)
4G to Wi-Fi hotspot conversion
NAPT network address translation support
Power management support
Automatic network recovery
SIM card detection and signal quality monitoring
Web configuration interface support
Supported Module Models:
The following table lists the supported 4G module models. They can be configured directly in menuconfig through the MODEM_TARGET macro. If the configuration is not effective, please select MODEM_TARGET_USER in menuconfig and manually configure the ITF interface.
Note
The same module may have multiple functional firmwares. Please consult the module manufacturer for PPP dial-up support.
Module Model |
|---|
ML302-DNLM/CNLM |
NT26 |
EC600NCNLC-N06 |
AIR780E |
MC610_EU |
EC20_CE |
EG25_GL |
YM310_X09 |
SIM7600E |
A7670E |
SIM7070G |
SIM7080G |
Setting up PPP Interface
The PPP interface is typically a USB CDC interface that must have a CDC data interface containing two bulk endpoints for input and output data. It may have a CDC notify interface with an interrupt endpoint, which is not used in this application code.
The PPP interface can be used for both AT command transmission and PPP data transfer, switching between them by sending “+++” data.
Example Descriptor
Most PPP interfaces have a bInterfaceClass of 0xFF (Vendor Specific Class). In the example below, the bInterfaceNumber of the PPP interface is 0x03.
Example USB descriptor:
Note
The following descriptor is an example. Not all descriptors follow this format exactly - some may include IAD interface descriptors or may not have interrupt endpoints.
*** Interface descriptor ***
bLength 9
bDescriptorType 4
bInterfaceNumber 3
bAlternateSetting 0
bNumEndpoints 3
bInterfaceClass 0xff
bInterfaceSubClass 0x0
bInterfaceProtocol 0x0
iInterface 8
*** Endpoint descriptor ***
bLength 7
bDescriptorType 5
bEndpointAddress 0x8a EP 10 IN
bmAttributes 0x3 INT
wMaxPacketSize 16
bInterval 16
*** Endpoint descriptor ***
bLength 7
bDescriptorType 5
bEndpointAddress 0x82 EP 2 IN
bmAttributes 0x2 BULK
wMaxPacketSize 64
bInterval 0
*** Endpoint descriptor ***
bLength 7
bDescriptorType 5
bEndpointAddress 0x1 EP 1 OUT
bmAttributes 0x2 BULK
wMaxPacketSize 64
bInterval 0
After identifying the PPP interface, you can configure MODEM_TARGET as MODEM_TARGET_USER and set MODEM_USB_ITF to the bInterfaceNumber of the PPP interface.
Dual PPP Interface
To enable AT command transmission while transferring data, you can use two PPP interfaces - one for data transfer and another for AT commands. This requires additional configuration of MODEM_USB_ITF2.
Note
The availability of a second AT command interface depends on the device.