AI 生成的摘要: Firmware Over-the-Air (FOTA) upgrade enables reliable remote updates of cellular modems throughout their lifecycle. It supports two triggering methods: device-initiated via proprietary AT commands and network-scheduled via LwM2M using AVSystem. The FOTA process involves four main actors: modem provider, device maker, end-product operator, and FOTA service provider. The document details the architecture, activation during manufacturing, client-server management, and the upgrade procedure, including key generation and device configuration for secure communication.