Communications Protocol
The communications protocol works in two modes: standard and extended. The primary difference between the two modes is that the extended mode adds source and destination address fields to the frame. The standard frame mode would normally be used in the case where there is only one piece of exercise equipment attached to one computer. This mode is primarily useful in a home setting where there is only one piece of exercise equipment and one controlling computer.
The extended mode is intended for use where multiple pieces of exercise equipment are attached to one or more computers via a shared link. This mode is useful in a gym setting with multiple pieces of exercise equipment located far away from the controlling computer. All of the equipment could be connected to a single multiplexing box which in turn connects to the controlling computer over a long cable.
Read more about this topic: Communications Specification For Fitness Equipment