---
title: "Congestion Avoidance and Control"
description: "This paper asks how TCP can keep a busy network useful when delay, packet loss, and retransmission tempt every sender to add even more traffic. Read it to see how acknowledgements become a clock, how slow start fills an empty path without a full-window burst, and why a congestion signal should make the sender retreat quickly before probing capacity again."
canonical_url: "https://fanout.sh/daily/2026-08-13-congestion-avoidance-control"
md_url: "https://fanout.sh/daily/2026-08-13-congestion-avoidance-control.md"
last_updated: "2026-08-13"
access: "public"
---

# Congestion Avoidance and Control

This paper asks how TCP can keep a busy network useful when delay, packet loss, and retransmission tempt every sender to add even more traffic. Read it to see how acknowledgements become a clock, how slow start fills an empty path without a full-window burst, and why a congestion signal should make the sender retreat quickly before probing capacity again.

## Paper details

- Authors: Van Jacobson

- Venue: SIGCOMM 1988

- Track: Systems

- Difficulty: Easy

- Reading time: 35 min

- Original paper: https://doi.org/10.1145/52324.52356

## What you will learn

- How ACK spacing carries the bottleneck's packet rhythm back to the sender, so one departing packet can clock one replacement into the network.

- Why slow start begins with one packet and grows from returned evidence instead of dumping a complete receiver window into an empty path.

- How additive increase, multiplicative decrease, RTT-variation estimation, and exponential timeout backoff interrupt the positive feedback behind congestion collapse.

## Continue exploring

[Explore TCP and UDP](https://fanout.sh/system/archive/tcp-vs-udp): Continue into Fanout's transport guide and connect congestion control to reliable byte streams, retransmission, flow control, head-of-line blocking, UDP, and QUIC.

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