SyntheticREDQueue (Javadocs [I2P+ 2.13.0+]

java.lang.Object
- net.i2p.util.SyntheticREDQueue

All Implemented Interfaces:
BandwidthEstimator
```
public class SyntheticREDQueue
extends Object
implements BandwidthEstimator
```
A "synthetic" queue that does not store data but estimates the average queue size assuming a fixed output bandwidth, and applies the Random Early Detection (RED) algorithm to decide probabilistically whether to accept or drop packets. The purpose is to model queue behavior and preemptively drop packets to prevent congestion before an actual queue is affected downstream. The average queue size is measured in bytes and is updated continuously, assuming the queue drains at a constant rate defined at construction. Packet acceptance is based on the RED algorithm, which uses the current average queue size and the offered packet size to calculate a drop probability. The drop probability is adjusted by a factor parameter and limited by configurable minimum and maximum queue size thresholds. This class also incorporates a Westwood+ bandwidth estimator that updates bandwidth estimates based on acknowledged packet sizes and timing, using an exponential weighted moving average (EWMA). Both bandwidth and queue size estimates are only updated when packets are accepted. The implementation is adapted from the Linux kernel tcp_westwood.c logic and follows established research including: - Random Early Detection Gateways for Congestion Avoidance (Floyd & Jacobson) - TCP Westwood: End-to-End Congestion Control for Wired/Wireless Networks (Casetti et al.) - End-to-End Bandwidth Estimation for Congestion Control (Grieco & Mascolo) Note: minThB (minimum threshold) must be less than maxThB (maximum threshold) for correct RED operation.

Constructor Summary

Constructors
Constructor and Description
`SyntheticREDQueue(I2PAppContext ctx, int bwBps)` Construct with default queue size thresholds based on bandwidth.
`SyntheticREDQueue(I2PAppContext ctx, int bwBps, int minThB, int maxThB)` Construct specifying bandwidth and queue size thresholds.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`addSample(int size)` Unconditionally accepts the given packet size.
`void`	`dispose()` Remove this instance from the tuning list.
`static void`	`expungeStaleInstances()` Remove cleared (GC'd) weak references from the list.
`float`	`getBandwidthEstimate()` Returns the current bandwidth estimate in bytes/ms.
`static float`	`getCurrentMaxDropProbability()` Returns current max drop probability across all instances.
`static int`	`getCurrentMaxThreshold()` Returns the maximum threshold from the first active instance, or -1 if none.
`static int`	`getCurrentMinThreshold()` Returns the minimum threshold from the first active instance, or -1 if none.
`static List<SyntheticREDQueue>`	`getInstances()` Returns a snapshot of all active SyntheticREDQueue instances.
`int`	`getMaxBandwidth()`
`float`	`getMaxDropProbability()` Returns the current max drop probability.
`int`	`getMaxThreshold()` Returns the current maximum threshold in bytes.
`int`	`getMinThreshold()` Returns the current minimum threshold in bytes.
`float`	`getQueueSizeEstimate()` Returns the current estimated average queue size in bytes.
`boolean`	`offer(int size, float factor)` Offer a packet to the queue.
`String`	`toString()` Returns a human-readable string displaying the current bandwidth and queue size estimates, formatted for debugging or informational output.
`static void`	`updateAllMaxDropProbability(float probability)` Update max drop probability on all active instances.
`static void`	`updateAllMaxThresholds(int threshold)` Update max threshold on all active instances.
`static void`	`updateAllMinThresholds(int threshold)` Update min threshold on all active instances.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - SyntheticREDQueue
```
public SyntheticREDQueue(I2PAppContext ctx,
                         int bwBps)
```
    Construct with default queue size thresholds based on bandwidth.
    Parameters:
    ctx - the I2P application context
    bwBps - nominal output bandwidth in bytes per second
  - SyntheticREDQueue
```
public SyntheticREDQueue(I2PAppContext ctx,
                         int bwBps,
                         int minThB,
                         int maxThB)
```
    Construct specifying bandwidth and queue size thresholds. Queue size thresholds: - minThB: queue size in bytes to start probabilistically dropping packets - maxThB: queue size in bytes at which all packets are dropped (100% drop probability) NOTE: minThB must be less than maxThB for proper operation.
    Parameters:
    ctx - the I2P application context
    bwBps - nominal output bandwidth in bytes per second
    minThB - minimum threshold queue size to start dropping (Bytes)
    maxThB - maximum threshold queue size to drop all packets (Bytes)
- Method Detail
  - addSample
```
public void addSample(int size)
```
    Unconditionally accepts the given packet size. Updates queue size and bandwidth estimates accordingly.
    Specified by:
    addSample in interface BandwidthEstimator
    Parameters:
    size - size of packet in bytes
  - dispose
```
public void dispose()
```
    Remove this instance from the tuning list. Called when the owning tunnel/queue is no longer active.
  - expungeStaleInstances
```
public static void expungeStaleInstances()
```
    Remove cleared (GC'd) weak references from the list.
  - getBandwidthEstimate
```
public float getBandwidthEstimate()
```
    Returns the current bandwidth estimate in bytes/ms. Updates estimate if enough time elapsed since last update.
    Specified by:
    getBandwidthEstimate in interface BandwidthEstimator
    Returns:
    bandwidth estimate in bytes/ms
  - getCurrentMaxDropProbability
```
public static float getCurrentMaxDropProbability()
```
    Returns current max drop probability across all instances.
    Returns:
    the current max drop probability
  - getCurrentMaxThreshold
```
public static int getCurrentMaxThreshold()
```
    Returns the maximum threshold from the first active instance, or -1 if none.
    Returns:
    the current max threshold
  - getCurrentMinThreshold
```
public static int getCurrentMinThreshold()
```
    Returns the minimum threshold from the first active instance, or -1 if none.
    Returns:
    the current min threshold
  - getInstances
```
public static List<SyntheticREDQueue> getInstances()
```
    Returns a snapshot of all active SyntheticREDQueue instances.
    Returns:
    the instances
  - getMaxBandwidth
```
public int getMaxBandwidth()
```
    Returns:
    the configured maximum bandwidth in bytes per second.
  - getMaxDropProbability
```
public float getMaxDropProbability()
```
    Returns the current max drop probability.
    Returns:
    the max drop probability
  - getMaxThreshold
```
public int getMaxThreshold()
```
    Returns the current maximum threshold in bytes.
    Returns:
    the max threshold
  - getMinThreshold
```
public int getMinThreshold()
```
    Returns the current minimum threshold in bytes.
    Returns:
    the min threshold
  - getQueueSizeEstimate
```
public float getQueueSizeEstimate()
```
    Returns the current estimated average queue size in bytes. Updates estimate if enough time elapsed since last update.
    Returns:
    queue size estimate in bytes
  - offer
```
public boolean offer(int size,
                     float factor)
```
    Offer a packet to the queue. The decision to accept or drop the packet is made based on RED algorithm using the current average queue size and the offered packet size with a drop probability. If packet is accepted, the queue size and bandwidth estimators are updated.
    Parameters:
    size - size in bytes of the packet
    factor - drop probability adjustment factor (1.0 for standard, 0 disables dropping)
    Returns:
    true if accepted, false if dropped
  - toString
```
public String toString()
```
    Returns a human-readable string displaying the current bandwidth and queue size estimates, formatted for debugging or informational output.
    Overrides:
    toString in class Object
    Returns:
    formatted status string including bandwidth and average queue size
  - updateAllMaxDropProbability
```
public static void updateAllMaxDropProbability(float probability)
```
    Update max drop probability on all active instances.
    Parameters:
    probability - new max drop probability (0.0 - 1.0)
  - updateAllMaxThresholds
```
public static void updateAllMaxThresholds(int threshold)
```
    Update max threshold on all active instances.
    Parameters:
    threshold - new maximum threshold in bytes (must be greater than min)
  - updateAllMinThresholds
```
public static void updateAllMinThresholds(int threshold)
```
    Update min threshold on all active instances.
    Parameters:
    threshold - new minimum threshold in bytes (must be less than max)

Class SyntheticREDQueue

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

SyntheticREDQueue

SyntheticREDQueue

Method Detail

addSample

dispose

expungeStaleInstances

getBandwidthEstimate

getCurrentMaxDropProbability

getCurrentMaxThreshold

getCurrentMinThreshold

getInstances

getMaxBandwidth

getMaxDropProbability

getMaxThreshold

getMinThreshold

getQueueSizeEstimate

offer

toString

updateAllMaxDropProbability

updateAllMaxThresholds

updateAllMinThresholds