RedDropper

simple 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 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 is 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 is 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.

Inheritance diagram

The following diagram shows inheritance relationships for this type. Unresolved types are missing from the diagram.

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).
DSQueue2	compound module	Diffserv Queue used in Experiment 2.1 - 2.4.
EthernetQosRedQueue	compound module	Queue module that gives the PAUSE frames a higher priority, and using Random Early Detection algorithm on data frames, and can be parametrized with an ~IPacketQueue for serving the data frames.
RedDropperQueue	compound module	Combines a packet queue with random early detection (RED) dropper.
REDQueue	compound module	(no description)

Used in

Name	Type	Description
RedDropperTutorialStep	network	(no description)

Extends

Name	Type	Description
PacketFilterBase	simple module	Base module for various packet filter modules. Derived modules must implement a single packet matcher function which determines if a packet is to be passed through or filtered out.

Parameters

Name	Type	Default value	Description
displayStringTextFormat	string	"dropped %d/%p pk (%k/%l)"	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
backpressure	bool	false
collectionModule	string	""
wq	double	0.002	Weight of the current queue length in the averaged queue length, in range [0.0, 1.0]
minth	double	5	Minimum threshold for average queue length
maxth	double	50	Maximum threshold for average queue length (=buffer capacity), in range (minth,packetCapacity]
maxp	double	0.02	Maximum value for pbs, in range [0.0, 1.0]
pkrate	double	150	Average packet rate for calculations when queue is empty
useEcn	bool	false	If enabled, packets are marked with ECN if applicable
packetCapacity	int	int(maxth)	Packets are dropped if queue length is greater

Properties

Name	Value	Description
class	RedDropper
display	i=block/downarrow

Gates

Name	Direction	Size	Description
in	input
out	output

Signals

Name	Type	Unit	Description
packetDropped	inet::Packet

Statistics

Name	Title	Source	Record	Unit	Interpolation Mode	Description
packetDropCongestion	packet drop: congestion	packetDropReasonIsCongestion(packetDropped)	count, sum(packetBytes), vector(packetBytes)		none

Source code

//
// 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 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 is 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
// is 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 extends PacketFilterBase
{
    parameters:
        string collectionModule = default("");
        double wq = default(0.002);  // Weight of the current queue length in the averaged queue length, in range [0.0, 1.0]
        double minth = default(5);  // Minimum threshold for average queue length
        double maxth = default(50);  // Maximum threshold for average queue length (=buffer capacity), in range (minth,packetCapacity]
        double maxp = default(0.02);  // Maximum value for pbs, in range [0.0, 1.0]
        double pkrate = default(150);  // Average packet rate for calculations when queue is empty
        bool useEcn = default(false); // If enabled, packets are marked with ECN if applicable
        int packetCapacity = default(int(maxth)); // Packets are dropped if queue length is greater
        @class(RedDropper);
        @display("i=block/downarrow");
        @signal[packetDropped](type=inet::Packet);
        @statistic[packetDropCongestion](title="packet drop: congestion"; source=packetDropReasonIsCongestion(packetDropped); record=count,sum(packetBytes),vector(packetBytes); interpolationmode=none);
}

File: src/inet/queueing/filter/RedDropper.ned