12.4.2 OTAU Basic Protocol and Control Flow

Once UAP (OTAU Server) appears on the network (assuming it possesses the necessary security material to join it), it must be discovered by the OTAU clients (upgradeable nodes), that implement the client side of the OTAU cluster. These client nodes issue periodic service discovery commands to discover the OTAU service cluster. In application scenarios where UAP is always present, this discovery will happen once when the client is powered on. Before clients can proceed with any OTAU specific actions, they must secure the link to the server. The security settings applied to this link are the same as the security requirements for ZigBee.

Once the link is secured, the clients can begin querying the server for the next image. If the server indicates that a new image is available, then a client starts requesting individual firmware image blocks or image pages consisting of multiple blocks from the server, eventually completing the download. When the download is complete, the server can tell the client when to actually begin running the new firmware image. The whole sequence of steps is illustrated in below Figure. If a client loses connection to the server, while it is loading an image, it will try to restore connection and continue downloading the image. The OTAU client cluster will try to get response from the server. If the server replies with information about the image of the same version as the image which downloading has been broken, the downloading will continue.