Passive TCP Congestion Window Estimation via ACK Analysis

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Solution Overview

Problem

Current technologies lack the capability to passively estimate a sender's congestion window throughout the life of a TCP flow, which is crucial for network traffic observation and troubleshooting.

Innovation Solution

A network monitoring system and method that observes network traffic to estimate the congestion window of a sender by analyzing the advertised window and outstanding data in flight, allowing for the determination of minimum and maximum congestion window values during a TCP flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If passive observation methodology is used to infer TCP connection characteristics, then network traffic analysis capability is improved, but measurement precision of congestion window is insufficient

Engineering Contradiction:

Improvenetwork traffic analysis capabilityVSAvoidcongestion window estimation accuracy

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

The patent uses ACK packets as intermediary carriers to extract congestion window information. By observing the ACK sequence numbers in packets passing through the network, the system can infer the sender's congestion window without directly accessing or interfering with the TCP stack, thus maintaining passive observation while improving measurement precision

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct mechanical access to TCP internal state with mathematical analysis of packet sequences. By analyzing the relationship between ACK sequence numbers and packet transmission patterns, the system substitutes physical access to congestion window data with computational inference, achieving precise measurement through passive observation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If active measurement methods are used to obtain congestion window data, then measurement precision is improved, but network traffic and system complexity increase

Engineering Contradiction:

Improvecongestion window data accuracyVSAvoidmonitoring system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent enables the monitoring system to extract all necessary information from existing network traffic packets that are already present in the network. The ACK packets themselves carry the congestion window information, eliminating the need for additional probe packets or complex active measurement sequences, thus reducing system complexity while maintaining precision

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent extracts congestion window information directly from the ACK packet sequence numbers without requiring additional measurement overhead. By taking out the relevant information from existing traffic packets, the system avoids the complexity of active measurement protocols while achieving accurate congestion window estimation

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentEP2523393B1Method and apparatus to estimate the sender's congestion window throughout the life of a TCP flow (socket connection)

Publication Date: 2014.11.26 FLUKE CORP

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AI summary

Network monitoring method and apparatus estimates the congestion window throughout the life of a TCP flow (socket connection), providing information useful for network performance analysis and troubleshooting.