computer science

Hierarchical fair-service curve

Hierarchical fair-service curve is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hierarchical fair-service curve rather than just read about it. In short: The hierarchical fair-service curve (HFSC) is a network scheduling algorithm for a network scheduler proposed by Ion Stoica, Hui Zhang, and T. S.

Key takeaways

Hierarchical fair-service curve belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hierarchical fair-service curve to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hierarchical fair-service curve from memory before moving on to harder problems.

Reference excerpt

The hierarchical fair-service curve (HFSC) is a network scheduling algorithm for a network scheduler proposed by Ion Stoica, Hui Zhang, and T. S. Eugene from Carnegie Mellon University at SIGCOMM 1997

In this paper, we propose a scheduling algorithm that to the best of our knowledge is the first that can support simultaneously (a) hierarchical link-sharing service, (b) guaranteed real-time service with provable tight delay bounds, and (c) decoupled delay and bandwidth allocation (which subsumes priority scheduling). This is achieved by defining and incorporating fairness property, which is essential for link-sharing, into Service-Curve based schedulers, which can decouple the allocation of bandwidth and delay. We call the hierarchical version of the resulted algorithm a Hierarchical Fair Service Curve (H-FSC) Algorithm. We analyze the performance of H-FSC and present simulation results to demonstrate the advantages of H-FSC over previously proposed algorithms such as H-PFQ and CBQ. Preliminary experimental results based on a prototype implementation in NetBSD are also presented. It is based on a QoS and CBQ. An implementation of HFSC is available in all operating systems based on the Linux kernel, such as e.g. OpenWrt, and also in DD-WRT, NetBSD 5.0, FreeBSD 8.0 and OpenBSD 4.6.

References

External links Hierarchical Packet Schedulers HFSC Scheduling with Linux HFSC Tutorial HFSC and VoIP « Maciej Bliziński

Worked examples

Example 1 — a first encounter with Hierarchical fair-service curve

Start with the simplest possible case. Write down what Hierarchical fair-service curve claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hierarchical fair-service curve before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hierarchical fair-service curve ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hierarchical fair-service curve

In research: Hierarchical fair-service curve appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hierarchical fair-service curve in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hierarchical fair-service curve is common in secondary-school and first-year university syllabi. It links to neighbouring topics Network performance, Network scheduling algorithms, Network software stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Hierarchical fair-service curve outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hierarchical fair-service curve in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hierarchical fair-service curve means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hierarchical fair-service curve out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hierarchical fair-service curve in simple terms?

The hierarchical fair-service curve (HFSC) is a network scheduling algorithm for a network scheduler proposed by Ion Stoica, Hui Zhang, and T. S.

Why does Hierarchical fair-service curve matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hierarchical fair-service curve?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hierarchical fair-service curve.