RFC 5681 - TCP Congestion Control

Document Information

• RFC Number: 5681
• Title: TCP Congestion Control
• Authors: M. Allman, V. Paxson, E. Blanton
• Date: September 2009
• Status: Standards Track
• Obsoletes: RFC 2581
• Updates: RFC 793

Abstract

This document defines TCP's four intertwined congestion control algorithms: slow start, congestion avoidance, fast retransmit, and fast recovery. In addition, the document specifies how TCP should begin transmission after a relatively long idle period, as well as discussing various acknowledgment generation methods. This document obsoletes RFC 2581.

Table of Contents

• 1. Introduction
• 2. Definitions
• 3. Congestion Control Algorithms
  • 3.1. Slow Start and Congestion Avoidance
  • 3.2. Fast Retransmit/Fast Recovery
• 4. Additional Considerations
  • 4.1. Restarting Idle Connections
  • 4.2. Generating Acknowledgments
  • 4.3. Loss Recovery Mechanisms
• 5. Security Considerations
• 6. Changes between RFC 2001 and RFC 2581
• 7. Changes Relative to RFC 2581
• 8. Acknowledgments
• 9. References

Key Algorithms

This RFC standardizes four critical TCP congestion control mechanisms:

1. Slow Start: Gradually increases the congestion window to probe network capacity
2. Congestion Avoidance: Linear increase of window after reaching threshold
3. Fast Retransmit: Quick loss detection using duplicate ACKs
4. Fast Recovery: Maintains throughput during loss recovery

Copyright Notice

Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved.

Status of This Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements.