---
title: "Congestion Control and Sharing a Link"
description: "In a loss-based congestion-control model, a sender probes for available capacity by raising its rate while packets arrive, then backs off when congestion signals appear. The rule helps senders share a"
canonical: https://lightmysky.com/learn/computing/congestion-control-and-sharing-a-link-mt_y5hPUrdKyq
source: https://lightmysky.com/learn/computing/congestion-control-and-sharing-a-link-mt_y5hPUrdKyq.md
retrieved: 2026-11-12
---

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# Congestion Control and Sharing a Link

In a loss-based congestion-control model, a sender probes for available capacity by raising its rate while packets arrive, then backs off when congestion signals appear. The rule helps senders share a link, while loss remains a signal rather than proof of one cause.

Subject: Computing · Area: Networks & Security · Ages 18 to 20
Page: https://lightmysky.com/learn/computing/congestion-control-and-sharing-a-link-mt_y5hPUrdKyq

## Ready when they can

- Explain why a sender treats a loss as a congestion signal in this model
- Describe how the sending rate rises and falls when the rule repeats
- Say what happens if one sender ignores backoff while others share the link

## Lesson: Sharing one link without overload

In a loss-based congestion-control model, a sender cannot see unused capacity directly. It probes by raising its sending rate while acknowledgements arrive. A loss is treated as a sign that the path may be congested, so the sender backs off. Loss can have other causes, but this model uses it as a congestion signal.

*(drawing: The sender cuts its rate after a loss, then probes again.)*

The classic additive-increase, multiplicative-decrease pattern makes a sawtooth. The rate grows by small steps while traffic gets through. On a congestion signal, it drops by a larger fraction, then grows again.

A shared queue has limited space. If one sender never backs off, it can occupy more of the queue. Other senders lose room, delays rise, and losses can spread. The link has not gained capacity.

**Recap.** The sender probes with small increases, cuts back after a congestion signal, and shares queue space with other senders.

*Original instructional content authored for os-taxonomy.*

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Reliable Delivery over an Unreliable Network](https://lightmysky.com/learn/computing/reliable-delivery-over-an-unreliable-network-mt_kCM411CSac)

## Opens up

- [Naming: DNS and the Resolution Path](https://lightmysky.com/learn/computing/naming-dns-and-the-resolution-path-mt_omttmGkEgW)