Data on the network moves at 250 kbps – about five times faster than a fast modem. All data is sent in packets consisting of a 21 bit header and up to eight bytes of data. If the network bandwidth is 100% utilized there may be up to about 3000 packets transmitted per second.
The header identifies the contents of the packet – that is, what kind of data is enclosed. It also identifies the sender, and in some cases the intended recipient. Finally, it includes the “priority” - higher priority packets get transmitted before lower priority packets.
The details of how the CAN protocol determines which node gets to transmit at each moment are handled by the CAN Controller in the node hardware. The details are unimportant here, except that it must be noted that it relies on every node having a unique address. This “Source Address” is a number up to 255, and assigning this address is a key part of the RV-C implementation.