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Tail drop

Tail drop 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 Tail drop rather than just read about it. In short: Tail drop is a simple queue management algorithm used by network schedulers in network equipment to decide when to drop packets. With tail drop, when the queue is filled to its maximum capacity, the newly arriving packets are dropped until the queue has enough room to accept incoming traffic.

Key takeaways

  • Tail drop 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 Tail drop to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Tail drop from memory before moving on to harder problems.

Reference excerpt

Tail drop is a simple queue management algorithm used by network schedulers in network equipment to decide when to drop packets. With tail drop, when the queue is filled to its maximum capacity, the newly arriving packets are dropped until the queue has enough room to accept incoming traffic. The name arises from the effect of the policy on incoming packets. Once a queue has been filled, the router begins discarding all additional datagrams, thus dropping the tail of the sequence of packets. The loss of packets causes the TCP sender to enter slow start, which reduces throughput in that TCP session until the sender begins to receive acknowledgements again and increases its congestion window. A more severe problem occurs when datagrams from multiple TCP connections are dropped, causing global synchronization; i.e. all of the involved TCP senders enter slow-start. This happens because, instead of discarding many segments from one connection, the router would tend to discard one segment from each connection.

See also Random early detection Weighted random early detection

Further reading Comer, Douglas E. (2005-07-10). Internetworking with TCP/IP (5 ed.). Prentice Hall. ISBN 978-0131876712..

Worked examples

Example 1 — a first encounter with Tail drop

Start with the simplest possible case. Write down what Tail drop 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 Tail drop 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 Tail drop 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 Tail drop

In research
Tail drop 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 Tail drop 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
Tail drop is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer network stubs, Routing, so understanding it makes those chapters shorter.
In everyday life
Look for Tail drop 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 Tail drop in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Tail drop means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Tail drop out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tail drop in simple terms?

Tail drop is a simple queue management algorithm used by network schedulers in network equipment to decide when to drop packets. With tail drop, when the queue is filled to its maximum capacity, the newly arriving packets are dropped until the queue has enough room to accept incoming traffic.

Why does Tail drop 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 Tail drop?

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 Tail drop.

Tags

  • Computer network stubs
  • Routing

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