Discrete Rate vs Discrete Event Simulation
Same Family, Different Answers on a Fast Line

Both methods are event-driven. They differ in what counts as an event, and that decides how each one copes once a line runs faster than a few units a minute. Here’s what each does well, where each breaks down and how to choose.

What counts as an event

Discrete event simulation (DES) models the system as a sequence of events involving individual entities. Each unit moving through the system is an event the simulator schedules, runs and cleans up, and the clock jumps from one event to the next.

Discrete rate simulation (DRS) models flow as a rate. Between rate-changing events such as failures, changeovers, blocking and starving, the rate is constant and buffer levels change linearly. The simulator does no work until something actually changes.

So in DES each unit is an event, and in DRS each rate change is an event while the units between events flow through as a continuous stream.

Side by side

When discrete event is the right tool

Discrete event simulation is the right method whenever unit identity matters. That includes queueing networks where you care about specific customers and their waits, supply chain models that track individual orders, call centers where each interaction has its own attributes, and baggage handling where each bag routes through scanners and conveyors. Discrete rate adds a method for rate-based systems where DES struggles. It doesn’t replace DES.

Where discrete event struggles on high-speed lines

Computational cost grows with throughput

A bottling line running 1,200 cans a minute produces 1,200 events a minute per station in a DES model, so a six-station line produces about 7,200 events a minute. A shift produces millions, and real-line micro-stops such as three-second jams, label misreads and sensor faults add more. A model that takes overnight to run makes it hard to decide anything within days.

Knock-on effects get averaged away

The standard way out is to model at a coarser scale. Short stops get rolled into one downtime parameter, or the whole line is treated as one constraint with a reduced rate. That buys speed at the cost of the dynamics. You lose how a two-minute stop at station four shows up as starving at station two a little later, and those effects often decide real-line OEE.

Blocking and starving are approximated

DES handles blocking through entity logic. An entity finishes at one station, can’t enter the next and waits in a queue. The mechanics work, but the timing of how a stop spreads is approximated. Discrete rate computes blocking and starving by propagating flow through the buffer network.

The validation evidence

The 2020 Winter Simulation Conference paper High Accuracy Discrete Rate and Reliability Modeling to Drive Improvement of Plant OEE and Throughput (Fischel and Lange) reported a discrete rate model within 1% of a real food plant’s measured OEE. The paper’s co-author Tom Lange spent 36 years in manufacturing R&D, retiring as Director of Modeling & Simulation in Corporate R&D. See the published OEE validation case study.

Choosing between them

Use discrete event simulation when

• Individual identity matters, such as specific orders, customers or parts.
• Throughput is low enough that per-unit events are cheap to compute.
• You’re modeling queueing networks, call centers, baggage handling or dispatch.
• You need to track unit-level attributes through the system.

Use discrete rate simulation when

• Flow rate matters more than the identity of individual units.
• Lines run hundreds or thousands of units a minute, where DES becomes impractical.
• The process is continuous or bulk flow, such as chemicals, food and beverage, paper or pipelines.
• Knock-on effects from micro-stops drive performance, and buffer design and decoupling are central questions.

Which tools use which method

Simulation software is usually built around one primary method, even when it offers others. The table groups widely known tools by that primary method, using each vendor’s own description of its product. Most general-purpose packages are discrete event at their core, and several add flow, fluid or agent-based features. For discrete-part manufacturing, job shops, warehousing and material handling, a discrete event tool is usually the right choice. Discrete rate earns its place on high-speed and bulk-flow lines.

Vendor descriptions are quoted from each product’s own web pages as of September 2026. Product lines change, so check the vendor for current capabilities. ExtendSim® is a registered trademark of Andritz Inc. Arena, FlexSim, Simul8, Simio, Siemens Tecnomatix Plant Simulation and AnyLogic are trademarks of their respective owners, referenced for identification only, with no affiliation or endorsement implied.

What it looks like in code

The two methods make different choices about the simulator’s main loop. A DES simulator keeps a priority queue of events ordered by time. The main loop pops the next event, processes it (which may schedule more events) and advances the clock. Every unit transit is its own event.

A DRS simulator keeps the current rate of every flow, plus a queue of predicted rate changes. When will this buffer fill? When will this interrupt fire? When does the next changeover start? The main loop pops the next predicted event, recomputes the affected rates and buffer levels directly, and predicts the next event. Between events it does nothing, because rates are constant and buffers change linearly.

Frequently asked questions