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A PHP implementation of QUIC protocol congestion control algorithms, supporting NewReno and BBR algorithms for high-performance network communication.

Table of Contents

• Features
• Installation
• Quick Start
• Testing
• Performance Features
• API Documentation
• Dependencies
• Contributing
• License
• Development Status

Features

Supported Congestion Control Algorithms

1. NewReno Algorithm

   • Traditional loss-based congestion control
   • Slow start and congestion avoidance mechanisms
   • Fast retransmit and fast recovery
   • Ideal for stable network environments

2. BBR Algorithm

   • Google's model-based congestion control
   • Bandwidth estimation and RTT measurement
   • Four states: startup, drain, probe_bw, probe_rtt
   • Optimized for high-bandwidth networks

Core Components

• CongestionControlInterface: Standard interface for congestion control algorithms
• CongestionWindow: Congestion window management class
• CongestionController: Congestion control coordinator
• NewReno: NewReno algorithm implementation
• BBR: BBR algorithm implementation

Installation

Requirements

• PHP 8.1 or higher
• tourze/quic-core package
• tourze/quic-recovery package

Using Composer

composer require tourze/quic-congestion

Quick Start

Basic Usage

<?php

use Tourze\QUIC\Congestion\NewReno;
use Tourze\QUIC\Congestion\BBR;
use Tourze\QUIC\Congestion\CongestionController;

// Using NewReno algorithm
$newReno = new NewReno();
$controller = new CongestionController($newReno);

// Sending a packet
$controller->onPacketSent(1, 1200, microtime(true));

// Receiving ACK
$controller->onPacketAcked(1, 1200, $sentTime, microtime(true));

// Check if can send
if ($controller->canSend(1200)) {
    // Can send packet
}

// Switch to BBR algorithm
$bbr = new BBR();
$controller->switchAlgorithm($bbr);

Using BBR Algorithm

<?php

use Tourze\QUIC\Congestion\BBR;

$bbr = new BBR(12000); // Initial congestion window 12KB

// Handle packet acknowledgment
$bbr->onPacketAcked($packetNumber, $bytes, $sentTime, $ackTime);

// Get sending rate
$pacingRate = $bbr->getSendingRate();

// Get detailed statistics
$stats = $bbr->getStats();
echo "Current state: " . $stats['state']; // startup, drain, probe_bw, probe_rtt
echo "Bandwidth estimate: " . $stats['bandwidth_estimate'] . " bytes/s";
echo "Min RTT: " . $stats['min_rtt'] . " seconds";

Congestion Window Management

<?php

use Tourze\QUIC\Congestion\CongestionWindow;

$window = new CongestionWindow();

// Slow start growth
$window->onPacketAcked(1200, true); // In slow start phase

// Congestion avoidance growth
$window->onPacketAcked(1200, false); // In congestion avoidance phase

// Handle packet loss
$window->onPacketLost();

// Get current window size
$size = $window->getWindowSize();

Testing

The package includes comprehensive test coverage with 58 unit tests and 163 assertions covering:

BBR Algorithm Tests (17 tests)

• Initial state validation
• Packet sending and acknowledgment
• RTT measurement and bandwidth estimation
• State transition mechanisms
• Packet loss handling
• Statistics accuracy

NewReno Algorithm Tests (13 tests)

• Slow start and congestion avoidance
• Fast retransmit and fast recovery
• Packet loss detection and window adjustment
• Duplicate ACK handling
• Timeout retransmission

Congestion Window Tests (11 tests)

• Window initialization and growth
• Minimum/maximum window limits
• Window reduction after packet loss
• Statistics collection

Congestion Controller Tests (14 tests)

• Algorithm switching functionality
• Batch ACK and loss handling
• RTT calculation and statistics
• Edge case handling
• Performance metrics collection

Running Tests

./vendor/bin/phpunit packages/quic-congestion/tests

Performance Features

• High-frequency packet processing support
• Memory usage optimization with automatic history cleanup
• Precise bandwidth and RTT measurement
• Configurable algorithm parameters
• Detailed performance statistics

API Documentation

CongestionControlInterface

interface CongestionControlInterface
{
    public function onPacketAcked(int $packetNumber, int $bytes, float $sentTime, float $ackTime): void;
    public function onPacketLost(int $packetNumber, int $bytes, float $sentTime, float $lossTime): void;
    public function onPacketSent(int $packetNumber, int $bytes, float $sentTime): void;
    public function getCongestionWindow(): int;
    public function getSlowStartThreshold(): int;
    public function canSend(int $bytes, int $bytesInFlight): bool;
    public function getSendingRate(): ?float;
    public function isInSlowStart(): bool;
    public function reset(): void;
    public function getStats(): array;
    public function getAlgorithmName(): string;
}

Dependencies

• tourze/quic-core: QUIC protocol core components
• tourze/quic-recovery: Packet loss detection and RTT estimation

Contributing

Please see CONTRIBUTING.md for details on how to contribute to this project.

License

The MIT License (MIT). Please see License File for more information.

Development Status

✅ Complete - All core features implemented and tested

• NewReno congestion control algorithm
• BBR congestion control algorithm
• Congestion window management
• Congestion controller coordination
• Complete unit test coverage