Other application model

Use the Other application model in cases where you do not want to use the Web model (you might, for example, wish to modify it for some special application needs, but you still want to keep the Web model for normal Web traffic), but where you are forced to use TCP type measurement.

The following parameters control the behavior of the other application model:

• delay - determines how the moving average of delay is calculated. The half-life parameter controls the smoothness of the delay moving average. A high value results in smaller changes in the calculated average delay because the delay contribution of past measurements is greater than when half-life is set low. This parameter does not affect decision-maker’s calculations, and is used only by the reporting module.
• hrtt - determines how handshake round trip time influences decision-maker’s calculations. The metric-contribution affects the weighting of the measured hrtt. Its value determines the mid-point of a curve that tells decision-maker how strictly it should regard measured hrtt in its decisions. A higher number for this value places greater importance on it (for example, an application is considered to be affected more by longer handshake round trip times).
• loss half-life - controls the smoothing factor of measured loss. A high value results in a smaller contribution of past loss events. This parameter does not affect decision-maker’s calculations, and is used only by the reporting module.
• short-term-loss - measures the observed loss in the last window-width packets received. Also uses a threshold to compare against the number of losses in the window to determine if there is loss. Below threshold short-term-loss is 0, above threshold it equals num losses / window-width.

For the other application model, application performance is derived from handshake round trip time (HRTT). Table 32 shows how HRTT correlates with the decision metric and application performance, from best (*****) to worst (*). The CNA system’s default values for HRTT are shown, but you can adjust the metric-contribution of HRTT when needed, in the same way as explained in the enterprise model for application-delay above.