OTA upgrade process

The OTA upgrade process is performed by sending OTA commands between the client and server. OTA commands are sent as explicitly addressed packets, as described in OTA commands.

To initiate an OTA upgrade, the upgrade server sends an Image Notify Command, either to a single device or as a broadcast. After that initial transmission, the OTA process is driven by the client—or clients, if the Image Notify command is sent as a broadcast and accepted by multiple clients. The client sends requests to the server to request the image information, download it, and request when to upgrade. If the client does not receive a response from the server, it retries its request a few times before aborting the upgrade. The requests sent by the client are designed so that the server does not have to store any state related to a client's upgrade in progress—it only needs to send the image notify and respond to requests as they come in. The server can still observe these requests to track the state of an upgrade if desired, however—for example, to report download progress.

The following diagram shows the sequence of transmissions for an OTA upgrade: