With respect to Open System Interconnection model (OSI), J1708 defines the physical layer.
The standard defines a 2-wire 18 gauge wire cable that can run up to 130 feet (40 m) and operates at 9600 bit/s.
The hardware utilized are RS-485 transceivers wired for open collector operation through the use of a pullup and pulldown of the separate data lines.
Transmission is accomplished by controlling the driver enable pin of the transceiver.
This method allows multiple devices to share the bus without the need for a single master node.