Principle (Minimum Buffer): In an open system for a given release rate there exists a minimum buffer size (may be zero) below which the line becomes unstable.
In an open system without buffer restrictions, throughput is set by the release rate, provided that the capacity of the line is larger than the release rate. However, if we impose finite buffers in the system, then blocking will reduce the capacity of the system. If the blocking becomes too severe, the line will not be able to keep up and hence its queue (backlog) will grow without bound. Depending on the capacity and variability of the stations, the line may be able to keep up with the desired release rate even without any inter-station buffering. But as release rate increases, the necessary buffer size will become larger than zero.
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