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RED Drop Profiles

A drop profile is a feature of the random early detection (RED) process that allows packets to be dropped before queues are full. Drop profiles are composed of two main values—the queue fullness and the drop probability. The queue fullness represents percentage of memory used to store packets in relation to the total amount that has been allocated for that queue. The drop probability is a percentage value that correlates to the likelihood that an individual packet is dropped from the network. These two variables are combined in a graph-like format.

When a packet reaches the head of the queue, a random number between 0 and 100 is calculated by the device. This random number is plotted against the drop profile having the current queue fullness of that particular queue. When the random number falls above the graph line, the packet is transmitted onto the physical media. When the number falls below the graph line, the packet is dropped from the network.

When you configure the RED drop profile on an interface, the queue no longer drops packets from the tail of the queue (the default). Rather, packets are dropped after they reach the head of the queue.

You specify drop probabilities in the drop profile section of the class-of-service (CoS) configuration hierarchy and reference them in each scheduler configuration. For each scheduler, you can configure multiple separate drop profiles, one for each combination of loss priority (low, medium-low, medium-high, or high) and IP transport protocol (TCP or non-TCP).

You can configure a maximum of 32 different drop profiles.

To configure RED drop profiles, include the following statements at the [edit class-of-service] hierarchy level of the configuration:



[edit class-of-service]
drop-profiles {



profile-name {
fill-level percentage drop-probability percentage;


interpolate {
drop-probability [ values ];
fill-level [ values ];
}


}


}

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