Buffers

Buffer nodes represent storage within a ReliaSim model. They are used to hold material between processing steps, allowing flow to decouple between upstream and downstream operations. In real systems, buffers often correspond to inventory locations, queues, or staging areas, and in ReliaSim they play a critical role in shaping how variability propagates through the network.

Each buffer has a defined capacity and an internal volume that changes over time as material enters and exits. When downstream nodes are unavailable or operating more slowly, material accumulates in upstream buffers. Conversely, when upstream flow is interrupted, downstream buffers may empty and become starved. This interaction between buffers and constraints enables ReliaSim to naturally capture blocking, starvation, and accumulation without requiring explicit logic from the user.

Buffers are especially important for understanding system resilience. Larger buffers can help absorb variability by providing temporary storage during interruptions or slowdowns, but they also increase work-in-process and may mask underlying constraints. Smaller buffers reduce inventory but make the system more sensitive to downtime and rate imbalances. By adjusting buffer capacities and observing the resulting behavior, you can explore these tradeoffs and determine where storage adds value versus where it simply shifts problems elsewhere.

In addition to capacity, buffers can be initialized with starting volumes, allowing you to model systems that begin with inventory already in place. This is useful when simulating steady-state operations or evaluating short-term scenarios where existing material levels matter. Buffers also serve as the natural start and end points of most models: the first buffer typically represents unlimited supply entering the system, while the final buffer collects all output, providing a clear measure of total production.

When building a model, buffers are often placed between constraints to represent intermediate storage and decoupling. However, not every connection requires a buffer—overuse can obscure the true drivers of flow. A common modeling approach is to begin with minimal buffering, then add buffers selectively where real-world storage exists or where variability needs to be absorbed. ReliaSim makes the impact of these decisions visible through throughput, efficiency, and Replay, helping you understand how buffer placement and sizing influence overall system performance.

Every ReliaSim Model starts and ends with a Buffer. The starting buffer has infinite supply and capacity, and the ending buffer starts with zero supply and infinite capacity. This represents the beginning and end of your model window.