1. Communication Architecture

Overview

The communication architecture for the ASF project is designed to be industrial-grade, ensuring reliability, low latency, and high throughput for critical operations like Over-the-Air (OTA) updates and real-time monitoring.

Primary & Secondary Communication Stack

The system utilizes a multi-layered communication approach to ensure connectivity even in challenging environments.

Role	Technology	Why (Industrial Rationale)
Primary Uplink	Wi-Fi 802.11n (2.4 GHz)	Leverages existing infrastructure and provides high throughput necessary for OTA updates.
Peer-to-Peer	ESP-NOW	Provides deterministic, low-latency communication without dependency on an Access Point (AP).
Long-range Fallback	LoRa (External Module)	Ensures resilience at farm-scale distances where Wi-Fi may not reach.

Note: Zigbee on ESP32-S3 is currently not considered industrial-mature in ESP-IDF. ESP-NOW is the preferred choice for reliable peer-to-peer communication.

Application Protocol

To avoid the pitfalls of raw TCP sockets or unversioned custom protocols, the system adopts MQTT over TLS 1.2.

Item	Decision
Broker	Main Hub / Edge Gateway
QoS	QoS 1 (At least once delivery)
Retain	Used for configuration topics only
Payload	CBOR (Binary, versioned for efficiency and compatibility)
Topic Model	`/farm/{site}/{house}/{node}/...`

Why MQTT?

Store-and-Forward: Handles intermittent connectivity gracefully.
Built-in Keepalive: Monitors connection health automatically.
Industrial Tooling: Compatible with standard monitoring and management tools.
Native Support: Stable implementation within the ESP-IDF framework.

Heartbeat & Liveness

A formalized heartbeat mechanism is implemented to feed into predictive maintenance systems.

Interval: 10 seconds
Timeout: 3 missed heartbeats (30 seconds) triggers an "offline" status.
Payload includes: Uptime, firmware version, free heap memory, RSSI (signal strength), and an error bitmap.

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