Peer-to-Peer vs. Master/Slave

In a Master/Slave configuration (sometimes referred to as Primary/Secondary), one centralized "master" device handles all the logic, and controls all of the "slave" devices.

Each slave device typically requires a dedicated communications conduit back to the master device. In practice, this means a generous amount of wiring must be done to set up the average Master/Slave configuration. This tangle of wiring can be greatly alleviated, however, by placing all of the devices on a single network. Slave devices still must receive control from the master device, but communication can effectively be daisy-chained via the network.

Because all control processing happens in the master device, Master/Slave configurations sometimes suffer from bandwidth bottlenecking, as well as from the creation of a single point of failure. If the master device malfunctions, the entire system comes to a halt. Fortunately, because all the "smarts" in the system are centrally located in the master device, finding the physical location of the problem is relatively easy.

In a Peer-to-Peer configuration, control and communication is distributed among devices in the field. Each device communicates directly with the devices around it, without having to go through a master device. A master may be present for the purpose of monitoring the system and injecting commands, but its presence is not necessary for the peer devices to function.

Because each peer device is effectively both "master" and "slave," the potential for bandwidth bottlenecks is eliminated. Moreover, wiring is drastically simplified because peer devices can be daisy-chained, rather than tethered directly to a master device.

In a peer-to-peer configuration, if one device goes down, the other devices can continue to function normally. Each device knows what it is supposed to do, independent of the other devices. In practice, this can be both beneficial and frustrating. If you did not have a monitoring device in the system, you would have to check each peer device individually to find the point of failure.