ESP MODEM¶
+This component is used to communicate with modems in the command mode (using AT commands), as well as the data mode +(over PPPoS protocol). +The modem device is modeled with a DCE (Data Communication Equipment) object, which is composed of:
+-
+
DTE (Data Terminal Equipment), which abstracts the terminal (currently only UART implemented).
+PPP Netif representing a network interface communicating with the DTE using PPP protocol.
+Module abstracting the specific device model and its commands.
+
+-----+
+ | DTE |--+
+ +-----+ | +-------+
+ +-->| DCE |
+ +-------+ | |o--- set_mode(command/data)
+ | Module|--->| |
+ +-------+ | |o--- send_commands
+ +->| |
+ +------+ | +-------+
+ | PPP |--+
+ | netif|------------------> network events
+ +------+
+Modem components¶
+DCE¶
+This is the basic operational unit of the esp_modem component, abstracting a specific module in software, +which is basically configured by
+-
+
the I/O communication media (UART), defined by the DTE configuration
+the specific command library supported by the device model, defined with the module type
+network interface configuration (PPPoS config in lwip)
+
After the object is created, the application interaction with the DCE is in
+-
+
issuing specific commands to the modem
+switching between data and command mode
+
DTE¶
+Is an abstraction of the physical interface connected to the modem. Current implementation supports only UART
+PPP netif¶
+Is used to attach the specific network interface to a network communication protocol used by the modem. Currently implementation supports only PPPoS protocol.
+Module¶
+Abstraction of the specific modem device. Currently the component supports SIM800, BG96, SIM7600.
+Use cases¶
+Users interact with the esp-modem using the DCE’s interface, to basically
+-
+
Switch between command and data mode to connect to the internet via cellular network.
+Send various commands to the device (e.g. send SMS)
+
The applications typically register handlers for network events to receive notification on the network availability and +IP address changes.
+Common use cases of the esp-modem are also listed as the examples:
+-
+
examples/pppos_client– simple client which reads some module properties and switches to the data mode to connect to a public mqtt broker.
+examples/modem_console– is an example to exercise all possible module commands in a console application.
+examples/ap_to_pppos– this example focuses on the network connectivity of the esp-modem and provides a WiFi AP that forwards packets (and uses NAT) to and from the PPPoS connection.
+
Extensibility¶
+CMUX¶
+Implementation of virtual terminals is an experimental feature, which allows users to also issue commands in the data mode, +after creating multiple virtual terminals, designating some of them solely to data mode, others solely to command mode.
+DTE’s¶
+Currently we support only UART, but modern modules support other communication interfaces, such as USB, SPI.
+Other devices¶
+Adding a new device is a must-have requirement for the esp-modem component. Different modules support different commands,
+or some commands might have a different implementation. Adding a new device means to provide a new implementation
+as a class derived from GenericModule, where we could add new commands or modify the existing ones.