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Intermediate Topic 23 of 50 Computer Networks

Congestion Control

Adapting send rate to avoid overloading the network.

How it works

Congestion control keeps senders from overloading the network. TCP maintains a congestion window and grows it as acknowledgements arrive: slow start doubles it each round trip until a threshold, then congestion avoidance adds one segment per round trip. On loss it reduces the window, a pattern called additive increase, multiplicative decrease. Modern algorithms include Cubic, BBR and others that use delay or bandwidth estimates.

Step-by-step walkthrough

  1. The sender starts with a small congestion window.
  2. Slow start doubles it every round trip.
  3. At a threshold growth becomes linear.
  4. A packet loss signals congestion.
  5. The window is cut, often halved, and growth begins again, a sawtooth pattern.

Where it is used

It enables the internet to share links fairly and avoid collapse. Operators tune algorithms for data centers, satellite links and wireless networks.

Common pitfall

Treating loss as the only congestion signal misbehaves on lossy wireless links. Aggressive or non-conforming senders hurt others. Bufferbloat hides congestion through huge queues. Short flows never leave slow start. Choose algorithms suited to the path, use explicit congestion notification where supported and avoid opening many parallel connections to cheat fairness.

Where it fits in the course

Congestion Control is topic 23 of 50 in Computer Networks, rated Intermediate. It follows Flow Control. The next topic is Sliding Window Protocol.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Computer Networks quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Congestion Control?
Adapting send rate to avoid overloading the network. It belongs to Computer Networks and is an intermediate-level topic.
Where do people use Congestion Control?
It enables the internet to share links fairly and avoid collapse.
What is the most common mistake with Congestion Control?
Treating loss as the only congestion signal misbehaves on lossy wireless links.
What should I learn before this topic?
Start with Flow Control, the topic just before it in Computer Networks.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Computer Networks quiz.
Is Congestion Control hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Congestion Control?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Congestion Control?
Flow Control, Sliding Window Protocol, Three-Way Handshake are closely connected. The full list is in the related topics section of this page.
What should I study after Congestion Control?
Continue with Sliding Window Protocol, the next topic in Computer Networks.

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