Immediate transitions fire in zero time and are used to resolve logical choices (conflicts) with probabilities proportional to their weights. Timed transitions model durations like service times, failure rates, or propagation delays. The enabling rule is same as ordinary Petri nets: a transition is enabled if each input place has at least the required number of tokens, and no inhibitor place has a token.
| Type | Symbol | Timing | Weight | Priority | |------|--------|--------|--------|----------| | (exponential) | Filled white bar | Random delay ~ exp(rate) | Rate λ | Low | | Immediate | Thin black bar | Zero delay | Probabilistic weight | High | Immediate transitions fire in zero time and are
: Performance evaluation of computer systems, fault-tolerant systems, manufacturing workcells, communication protocols, and any system with concurrency, contention, and exponentially distributed events. | Type | Symbol | Timing | Weight