4.7. QoSiStates
Although our model can detect large, sudden changes close to QoSState boundaries, it can not spot slow gradual changes until they cross a boundary (this behaviour arises from our chosen definition of v_p). The application may like to have an indication when a QoSParam value in the NetQoSState is nearing a corresponding QoSState tuple _lo or _hi threshold. This would mean that the application is operating near a QoSState boundary (and so may soon need to change state). We can detect this through the use of QoS intermediate states or QoSiStates. These are quasi-states that do not represent a flow state as a QoSState does, but are an indication of the proximity of the QoSParam value to the _lo or _hi threshold of a QoSState. The QoSiState only exists within a QoSState, and is an optional part of the QoSState definition. A QoSiState is also specified by use of a boundary, _qlo or _qhi. The relationship of the QoSiState to the QoSState with respect to a single QoSParam, P, is depicted in Fig. 5. A QoSiState can only exist if it has a corresponding _lo or _hi defined in the QoSState.