So if you change the radio (even for one the same) the ECU is still sending commands addressed to the old radio's ID, and the new one will just ignore them because they aren't addressed to it. Therefore the ECU needs to know the CAN ID of the radio so it can send the message to it. Rather than having an Ignition Live wire to the radio, the ECU can send a 'turn on' message to the radio when the ignition is turned on. I think this is the issue when changing the radio.
(An ethernet network does have a host, the nameserver or DNS (normally in the router in a home network) which issues IP adresses to any device which joins the network to allow them to talk to each other) While going into the details of CAN bus is beyond the scope of this article, you can find the relevant information here. there a no master device which means that all devices must have a preset unique ID to identify themselves with. CAN (Controller Area Network) is another such protocol, which isnt very widely popular in general, but find several applications in the automotive domain. (Stritcly speaking the first device connects to the last device and all the intermediate devices branch off on a small stub.) and the first and last device must have a 120R termination resistor between the two CAN wires. The devices are connected together in a daisy chain, i.e. The basics are that it's a network to allow multiple devices to communicate over a pair of wires (a twisted pair), so to connect a CANBUS device you only need 4 wires - Power, Ground, CAN+ and CAN- (plus any inputs or outputs). I know a little bit about CANBUS, but not right into the technical detail, and not specifically as used in road cars/vans.
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