REDDropper

simple module

This module implements Random Early Detection (RED).

It has n input and n output gates (specified by the 'numGates' parameter). Packets arrived at the ith input gate are forwarded to the ith output gate, or dropped. The output gates must be connected to simple modules implementing the IQueueAccess C++ interface (e.g. FIFOQueue).

The module sums the used buffer space of the queues attached to the output gates. If it is below a minimum threshold, the packet won't be dropped, if above a maximum threshold, it will be dropped, if it is between the minimum and maximum threshold, it will be dropped by a given probability. This probability determined by a linear function which is 0 at the minth and maxp at maxth.

The queue length can be smoothed by specifying the 'wq' parameter. The average queue length used in the tests are computed by the formula:

avg = (1-wq)*avg + wq*qlen

The minth, maxth, and maxp parameters can be specified separately for each input gate, so this module can be used to implement different packet drop priorities.

Used in compound modules

Name	Type	Description
AFxyQueue	compound module	This is an example queue, that implements one class of the Assured Forwarding PHB group (RFC 2597).

Parameters

Name	Type	Default value	Description
numGates	int	1
wq	double	0.002	weight of the current queue length in the averaged queue length
minths	string	"5"	minimum thresholds for avg queue length (one number for each gate, last one repeated if needed)
maxths	string	"50"	maximum thresholds for avg queue length (=buffer capacity) (one number for each gate, last one repeated if needed)
maxps	string	"0.02"	maximum value for pbs (one number for each gate, last one repeated if needed)
pkrates	string	"150"	average packet rate for calculations when queue is empty

Properties

Name	Value	Description
display	i=block/downarrow

Gates

Name	Direction	Size	Description
in [ ]	input	numGates
out [ ]	output	numGates

Source code

//
// This module implements Random Early Detection (RED).
//
// It has n input and n output gates (specified by the 'numGates'
// parameter). Packets arrived at the ith input gate are
// forwarded to the ith output gate, or dropped. The output
// gates must be connected to simple modules implementing
// the IQueueAccess C++ interface (e.g. FIFOQueue).
//
// The module sums the used buffer space of the queues attached
// to the output gates. If it is below a minimum threshold,
// the packet won't be dropped, if above a maximum threshold,
// it will be dropped, if it is between the minimum and
// maximum threshold, it will be dropped by a given probability.
// This probability determined by a linear function which is
// 0 at the minth and maxp at maxth.
//
// The queue length can be smoothed by specifying the 'wq'
// parameter. The average queue length used in the tests
// are computed by the formula:
//
//  avg = (1-wq)*avg + wq*qlen
//
// The minth, maxth, and maxp parameters can be specified
// separately for each input gate, so this module can be
// used to implement different packet drop priorities.
//
simple REDDropper
{
    parameters:
        int numGates = default(1);

        double wq = default(0.002);  // weight of the current queue length in the averaged queue length
        string minths = default("5");  // minimum thresholds for avg queue length (one number for each gate, last one repeated if needed)
        string maxths = default("50");  // maximum thresholds for avg queue length (=buffer capacity) (one number for each gate, last one repeated if needed)
        string maxps = default("0.02");  // maximum value for pbs (one number for each gate, last one repeated if needed)
        string pkrates = default("150");  // average packet rate for calculations when queue is empty
        @display("i=block/downarrow");

    gates:
        input in[numGates];
        output out[numGates];
}

File: src/inet/common/queue/REDDropper.ned