The Congestion action determines how a backed-up send queue is handled. Since this queue cannot grow indefinitely, packets must be discarded at some point. Two mechanisms are available here: Designated as Taildrop, Random Early Detection (RED), or Random Early Discard. With taildrop, a limit is set beyond which all further incoming packets are discarded. In RED, two limits are determined. As of the first one, packets are discarded with a probability P. P increases the closer you get to the second limit. If the second limit is exceeded, all incoming packets are discarded, like taildrop.
The Conjestion action table is defined in such a way that RED and Taildrop can be configured passively. A taildrop can be recognized by the fact that the threshold minimum is equal to the threshold maximum. Max-Probability with a Taildrop has no purpose, but should be entered as 100 to specify that everything above the limit will be discarded.
You only specify the Metric-Type and Limit-Minimum, the other values are set so that a Taildrop is configured.
For a RED, the Limit-Minimum is not equal to Limit-Maximum. Starting from the Limit-Minimum, the probability of a packet being discarded is P = 0, with P linearly approaching Max-Probability the closer you get to the Threshold-Max.
In LANconfig, the limits for Congestion incidents are set under .
- Name
- The name of the Congestion-Action entered here is used to reference the entry from other tables. The name must be unique within this table.
- Metric type
- This specifies which metric is used by the values in columns Commit-Rate and Excess-Rate.
- Threshold minimum
- Specifies the lower threshold for the Congestion action.
- Threshold maximum
- Specifies the upper threshold for the Congestion action. From here on, all packets are discarded.
- Max. probability
- Specifies the maximum drop probability for a configured RED. Is ignored if there is a Taildrop and should be set to 100 there.
