# Shared Bottleneck Detecction Based on Trend Line Regression for Multipath Transmission

## TL;DR

This paper introduces a delay trend line regression method to detect shared bottlenecks in multipath transmission, enabling adaptive congestion control and significantly improving throughput in non-sharing scenarios while maintaining fairness.

## Contribution

It proposes a novel delay trend line regression technique for shared bottleneck detection in multipath protocols, enhancing throughput and fairness in congestion control.

## Key findings

- Achieves 74% throughput gain in non-sharing bottleneck scenarios.
- Effectively detects shared bottlenecks using delay trend line slopes.
- Maintains fairness in common bottleneck situations.

## Abstract

The current deployed multipath congestion control algorithms couple all the subflows together to avoid bandwidth occupation aggressiveness if the subflows of multipath transmission protocol share common bottleneck with single path TCP. The coupled congestion control algorithms can guarantee well fairness property in common bottleneck but result in rate increase conservativeness in none-sharing bottleneck situation. Thus, the throughput of multipath session can be further improved when combing with effective shared bottleneck detection mechanism. This paper proposes a delay trend line regression method to detect if flows share common bottleneck. Deduced from TCP fluid model, the packet round trip delay signal shows linear increase property during the queue building up process of the narrowest link and the delay trend line slopes of two flows are in close proximity if they traverse the same bottleneck link. The proposed method is implemented on multipath QUIC golang codebase and extensive simulations are performed to validate its effectiveness in detecting out flows traversing common bottleneck. If the subflows are detected out via a common bottleneck, the sender would perform coupled congestion control algorithm and perform congestion control seperately on flow level in none sharing bottleneck case. Results show a multipath session with two subflows can obtain 74\% gain on average in throughput compared with single path connection when Linked Increases Algorithm (LIA) is in combination with trend line regession shared bottlenck detection algorithm in none shared bottleneck, and show well fairness property in common bottleneck scenarios.