The History of Discrete Rate Simulation
Created by Andrew Siprelle in 1990

Discrete rate simulation began in 1990 as bulk flow simulation, a way to model fast production lines as rates instead of one unit at a time. It entered the peer-reviewed record in 1995, took its current name in the late 2000s, and has been published on and validated for three decades since.

1990: The three primitives

In 1990 the standard method was discrete event simulation, which treats every unit moving through a system as its own event. On a slow line, a few units a minute, that works. On a real production line running hundreds or thousands of units a minute, with micro-stops rippling downstream, discrete event models slowed to a crawl and averaged away the very behavior that mattered.

Andrew Siprelle took a different approach. Instead of tracking units, model flow as a rate, and describe the system with three building blocks:

• Constraints limit the rate of flow.
• Buffers absorb the difference between upstream and downstream rates.
• Interrupts change a rate: failures, changeovers, quality stops, each with its own time-to-failure and time-to-repair distributions.

Between interrupts the rates hold, so the simulator has nothing to recalculate. When something changes, the flow is recomputed directly. That one shift made fast, high-volume lines practical to simulate in detail. The three building blocks are explained in more depth on the main discrete rate page.

1995: The first paper

The method entered the academic record at the 1995 Winter Simulation Conference with Modeling a Bulk Manufacturing System Using Extend (Siprelle and Parsons). The paper applied the three-primitive approach to a real bulk-flow production problem and argued that rate-based modeling was a general method, not a special-purpose trick.

From bulk flow to discrete rate

For most of its first two decades the method wasn’t called discrete rate simulation. Andy’s original name, and the name on every foundational paper of the 1990s, was bulk flow simulation. The 1997 follow-up was Simulation of Bulk Flow and High Speed Operations (Siprelle and Phelps). The toolkit Andy released through Simulation Dynamics, Inc. in the late 1990s carried the name SDI Industry.

The new name took hold in the late 2000s, as the technique was built into commercial simulation software. It appears in Winter Simulation Conference paper titles from Imagine That: Damiron and Nastasi’s Discrete Rate Simulation Using Linear Programming (2008) and Krahl’s ExtendSim Advanced Technology: Discrete Rate Simulation (2009). By then the bulk flow approach had become a module of ExtendSim®.

The technique didn’t change; the name did. Constraints, buffers and interrupts are the same method under either name. The lineage page traces each era in detail, from Pritsker’s SLAM in 1979 to today.

Since 1995: The published record

Three decades of papers have extended, compared and validated the method. A selection:

The full bibliography, sixteen papers from 1995 to 2020, is on the lineage page.

What it became

Discrete rate simulation now ships in commercial simulation software, has been the subject of research at the Winter Simulation Conference and in Springer proceedings for three decades, and is used in manufacturing, process industries and logistics planning.

The 2020 Fischel and Lange model of a multi-line food plant was later rebuilt in ReliaSim and independently validated within 1% of the plant’s measured OEE. The published OEE validation case study has the details.

“It would take me up to a month to develop a digital twin for a production line using traditional methods. ChiAha’s discrete rate approach streamlines this process while still delivering high-quality results.”

Tom Lange, Technology Optimization & Management LLC, co-author of the 2020 validation paper

The tools today

The work continues at ChiAha, where discrete rate simulation runs:

• ReliaSim, simulation software for production lines, built on time-to-failure and time-to-repair data, with blocking and starving analysis and gain-versus-loss experiments.
• The Sandbox Flow tier, where you can run the classic discrete rate demos in your browser.
• The free Decoupling Buffer Simulator, a browser-based model of how buffers absorb upstream failures.

About Andrew Siprelle

Andrew Siprelle is the founder of ChiAha and the creator of discrete rate simulation. He has spent thirty-five years applying simulation, operations research and high-performance computing to real industrial systems, the kind of work where the answer has to match the line, not just a benchmark. He wrote the foundational 1995 Winter Simulation Conference paper and its 1997 follow-up on bulk flow and high-speed operations.