2.6.15.10.4.1 Abatement by Color/Priority
Since the DOIC Loss abatement algorithm is rate based, it is necessary for the DSR’s DOIC abatement algorithm to use rate based algorithm rather than the “threshold” (CL0-CL3) mechanisms currently used for ETGs/ETLs. The DOIC implementation of the loss abatement algorithm uses a Priority/Color mechanism similar to the one used for the DA-MP overload controls. It supports throttling by:
- Message priority only
- Message Priority first, then color
- Color first then Message Priority
For instance, if the abatement request is for a 10% reduction, rather than reducing all of the traffic by that rate, the DSR rejects from the lowest rank to the highest rank the requests to hit that target rate. The figure below shows an example of throttling by Priority. Based on the requested reduction in an OLR, the DSR calculates the Max ETR for that TTP. The DSR then start discarding the lower priority messages (in this case P0 messages) until it hits the required rate.
Figure 2-30 Throttle by Message Priority Only when support for 5 message priorities is enabled
If the customer has selected the “Discard by Priority within Color” option, then the DSR makes the same calculation about the Max ETR, but as shown in the figure below it starts discarding “yellow” messages from lowest to highest priority before it discards any “green” messages of any priority.
Figure 2-31 Throttle by Color then Message Priority when support for 5 message priorities is enabled
Supporting Color and Priority throttling requires the rate of each Color and Priority be tracked per TTP. These message rates track messages arriving at the TTP, and do not include ingress messages discarded by the Per-Connection Ingress MPS Control component or by DA-MP overload. These rates are tracked using the existing Sliding Historic Metric (SHM) that is used for other overload controls within the DSR. This SHM mechanism allows the user to set a “convergence” time for how quickly the rate metric reacts to changes in the rate. A small Rate Convergence Time causes the calculated rate to react to short term bursts, where a larger number “smooths” bursty traffic.
The discard policy for the TTP is inherited from the Congestion Discard Policy parameter set in the DA-MP profile for each DA-MP.