networks//network theory//determinism

A communication is deterministic when its timing is **predictable**, not merely fast. If a response usually takes 1 ms but occasionally takes 300 ms, it can be useless for a control loop even though its average looks excellent.

A communication is deterministic when its timing is predictable, not merely fast. If a response usually takes 1 ms but occasionally takes 300 ms, it can be useless for a control loop even though its average looks excellent.

The real-time recipe is low latency plus low jitter plus bounded worst case. Latency is how long a packet takes; jitter is how much that time varies; the bound is what a controller can actually plan around. Office networks and the public Internet optimize throughput and cost and give no bound at all (Latency, Throughput).

Industrial networks are built around this property: the PLC scan cycle is a bounded loop, industrial Ethernet variants add scheduling and synchronization to ordinary Ethernet, and an industrial switch is chosen for recovery time, not for port count.

The demand grows with the task: supervision tolerates seconds, a machine interlock needs milliseconds, coordinated motion control needs synchronized microseconds. Determinism is one of the three reasons a REST API is the wrong tool below the control layer (fault semantics).