PPP over Serial (PPPoS) client example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

Overview

A general PPP application consists of two parts: PPP server which is provided by cellular modem module and PPP client which is provided by ESP32 in this example. Standard operating systems like Windows and Unix integrate a full PPP stack and provide a way to setup PPP connection at the same time. But how can we get access to Internet by PPP protocol in a resource constrained system? Fortunately, the PPP protocol has already been implemented in lwIP, but it doesn't supply a common way to setup a PPP connection. This example introduces a library focusing on sending and parsing AT commands, and also provides useful functions to set up PPP connection. When PPP connection has been established, the IP packet flow from application side will be transmitted to Internet by cellular module. This example shows how to act as a MQTT client after the PPPoS channel created by using ESP-MQTT APIs.

How to use example

Hardware Required

To run this example, you need an ESP32 dev board (e.g. ESP32-WROVER Kit) or ESP32 core board (e.g. ESP32-DevKitC). For test purpose, you also need a cellular modem module. Here we take the SIM800L and BG96 as an example. You can also try other modules as long as they embedded PPP protocol.

Note: Since SIM800L only support 2G which will not work in some countries. And also keep in mind that in some other countries it will stop working soon (many remaining 2G networks will be switched off in the next 2-3 years). So you should check with your local providers for further details if you try this example with any 2G modules.

Pin Assignment

Note: The following pin assignments are used by default which can be changed in menuconfig.

ESP32	Cellular Modem
GPIO25	RX
GPIO26	TX
GND	GND
5V	VCC

Configure the project

Enter make menuconfig if you are using GNU Make based build system or enter idf.py menuconfig if you are using CMake based build system. Then go into Example Configuration menu.

• Choose the modem module in Choose supported modem device(DCE) option, currently we only support BG96 and SIM800L.
• Set the access point name in Set Access Point Name(APN) option, which should depend on the operator of your SIM card.
• Set the username and password for PPP authentication in Set username for authentication and Set password for authentication options.
• Select Send MSG before power off if you want to send a short message in the end of this example, and also you need to set the phone number correctly in Peer Phone Number(with area code) option.
• In UART Configuration menu, you need to set the GPIO numbers of UART and task specific parameters such as stack size, priority.

Note: During PPP setup, we should specify the way of authentication negotiation. By default it's configured to PAP. You can change to others (e.g. CHAP) in Component config-->LWIP-->Enable PPP support menu.

Build and Flash

Enter make -j4 flash monitor if you are using GNU Make based build system or enter idf.py build flash monitor if you are using CMake based build system.

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

The example will get module and operator's information after start up, and then go into PPP mode to start mqtt client operations. This example will also send a short message to someone's phone if you have enabled this feature in menuconfig.

BG96 Output

I (1276) pppos_example: Module: BG96
I (1276) pppos_example: Operator: "CHINA MOBILE CMCC"
I (1276) pppos_example: IMEI: 866425030121349
I (1276) pppos_example: IMSI: 460007454185220
I (1476) pppos_example: rssi: 27, ber: 99
I (1676) pppos_example: Battery voltage: 3908 mV
I (1876) pppos_example: Modem PPP Started
I (2656) pppos_example: Modem Connect to PPP Server
I (2656) pppos_example: ~~~~~~~~~~~~~~
I (2656) pppos_example: IP          : 10.65.71.127
I (2656) pppos_example: Netmask     : 255.255.255.255
I (2666) pppos_example: Gateway     : 10.64.64.64
I (2666) pppos_example: Name Server1: 211.136.112.50
I (2676) pppos_example: Name Server2: 211.136.150.66
I (2676) pppos_example: ~~~~~~~~~~~~~~
I (2686) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (2696) pppos_example: MQTT other event id: 7
I (3426) MQTT_CLIENT: Sending MQTT CONNECT message, type: 1, id: 0000
I (3856) pppos_example: MQTT_EVENT_CONNECTED
I (3856) pppos_example: sent subscribe successful, msg_id=20132
I (4226) pppos_example: MQTT_EVENT_SUBSCRIBED, msg_id=20132
I (4226) pppos_example: sent publish successful, msg_id=0
I (4646) pppos_example: MQTT_EVENT_DATA
TOPIC=/topic/esp-pppos
DATA=esp32-pppos
I (4696) pppos_example: Modem PPP Stopped
I (9466) pppos_example: Send send message [Welcome to ESP32!] ok
I (9666) pppos_example: Power down

SIM800L Output

I (1276) pppos_example: Module: SIMCOM_SIM800L
I (1276) pppos_example: Operator: "CHINA MOBILE"
I (1276) pppos_example: IMEI: 865992039850864
I (1276) pppos_example: IMSI: 460007454185220
I (1476) pppos_example: rssi: 25, ber: 0
I (1676) pppos_example: Battery voltage: 4674 mV
I (1876) pppos_example: Modem PPP Started
I (2806) pppos_example: Modem Connect to PPP Server
I (2806) pppos_example: ~~~~~~~~~~~~~~
I (2806) pppos_example: IP          : 10.188.173.2
I (2806) pppos_example: Netmask     : 255.255.255.255
I (2816) pppos_example: Gateway     : 192.168.254.254
I (2816) pppos_example: Name Server1: 211.136.112.50
I (2826) pppos_example: Name Server2: 211.136.150.66
I (2826) pppos_example: ~~~~~~~~~~~~~~
I (2836) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (2846) pppos_example: MQTT other event id: 7
I (8156) MQTT_CLIENT: Sending MQTT CONNECT message, type: 1, id: 0000
I (8826) pppos_example: MQTT_EVENT_CONNECTED
I (8826) pppos_example: sent subscribe successful, msg_id=26237
I (9526) pppos_example: MQTT_EVENT_SUBSCRIBED, msg_id=26237
I (9526) pppos_example: sent publish successful, msg_id=0
I (10326) pppos_example: MQTT_EVENT_DATA
TOPIC=/topic/esp-pppos
DATA=esp32-pppos
I (10376) pppos_example: Modem PPP Stopped
I (14526) pppos_example: Send send message [Welcome to ESP32!] ok
I (15076) pppos_example: Power down

Troubleshooting

1. Why sending AT commands always failed and this example just keeping rebooting? e.g.

E (626) sim800: sim800_sync(293): send command failed
E (626) sim800: sim800_init(628): sync failed

• Make sure your modem module is in command mode stably before you run this example.

(For any technical queries, please open an issue on GitHub. We will get back to you as soon as possible.)