In industrial robot networks, what distinguishes a deterministic communication protocol from a non-deterministic one?

The key distinction between a deterministic and a non-deterministic communication protocol in industrial robot networks lies in the predictability of message delivery times. A deterministic protocol guarantees that a message will be delivered within a known and bounded time interval. This means that the maximum time it takes for a message to travel from one device to another on the network can be precisely determined. This is crucial in real-time control applications where precise timing is essential, such as coordinating the movements of multiple robots or synchronizing a robot with other equipment like conveyors or sensors. Examples of deterministic protocols include EtherCAT and PROFINET IRT (Isochronous Real-Time). Conversely, a non-deterministic protocol does not guarantee a maximum message delivery time. While messages are typically delivered quickly, there is no upper limit on how long it might take for a message to reach its destination. This variability can be due to factors like network congestion or collisions. Non-deterministic protocols are suitable for applications where occasional delays are tolerable, such as data logging or remote monitoring, but they are generally unsuitable for real-time control. Examples of non-deterministic protocols include standard Ethernet/IP and Modbus TCP/IP. The predictability of deterministic protocols is achieved through mechanisms like time division multiple access (TDMA) or token passing, which ensure that each device on the network has a guaranteed time slot for transmitting data.