Walter Unified Communications Library

Introduction

Walter is a multi-radio IoT module combining an Espressif ESP32-S3 with a Sequans GM02SP cellular modem. Out of the box, a Walter module supports:

• Cellular: LTE Cat-M1, LTE Cat-NB1, LTE Cat-NB2
• Wi-Fi
• Bluetooth Low Energy
• GNSS: GPS and GLONASS

Unified Communications

The Walter Unified Communications library provides a high-level networking abstraction across multiple physical interfaces. Instead of targeting a specific modem or Wi-Fi stack, walter-uc introduces drivers:

• Cellular driver – based on PPP via the ESP-IDF esp-modem library (GM02SP)
• Wi-Fi driver – based on ESP-IDF Wi-Fi stack
• Future drivers – e.g. Ethernet, or other transport integrations

Each driver contributes a network interface. walter-uc monitors the state of all drivers and automatically selects the most favorable one according to priority and availability.

From the application perspective, this means you can continue to use the standard ESP-IDF networking APIs (sockets, MQTT, HTTP, etc.) without worrying about which underlying transport is currently active.

Key Features

• Seamless driver selection Transparent switching between Wi-Fi, LTE-M/NB-IoT, and future interfaces like Ethernet.

• Transparent error handling Built-in recovery and retry mechanisms per driver.

• Protocol independence Applications keep using standard APIs (socket, MQTT, HTTP, etc.), regardless of the active transport.

• Certificate management Unified handling of TLS certificates across drivers.

Application Responsibility

While walter-uc ensures there is always an active, working network interface, connection continuity remains the responsibility of the application.

Switching between drivers may result in a new IP address, which invalidates existing higher-level sessions. Your application must:

• Detect when the active driver changes
• Re-establish sessions (e.g. MQTT, TCP sockets, CoAP, …) as necessary

This design provides robustness and flexibility while maintaining compatibility with the ESP-IDF networking stack.

Repository Structure

C:.
│   .clang-format
│   .gitignore
│   CMakeLists.txt
│   idf_component.yml
│   Kconfig
│   README.md
│
├───docs
│       Architecture.pdf
│
├───examples
│   ├───bluecherry
│   ├───mqtt
│   └───udp-socket
│
└───src
    │   uc.cpp
    │   uc.hpp
    │   utils.h
    │
    ├───bsp
    └───driver

• docs/ – Reference architecture documentation
• examples/ – Example applications (BlueCherry, MQTT, UDP socket)
• src/ – Core library, board support, and drivers