computer science

Out-of-order delivery

Out-of-order delivery 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 Out-of-order delivery rather than just read about it. In short: In computer networking, out-of-order delivery is the delivery of data packets in a different order from which they were sent. Out-of-order delivery can be caused by packets following multiple paths through a network, by lower-layer retransmission procedures (such as automatic repeat request), or via parallel processing paths within network equipment that are not designed to ensure that packet ordering is preserved.

Key takeaways

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

Reference excerpt

In computer networking, out-of-order delivery is the delivery of data packets in a different order from which they were sent. Out-of-order delivery can be caused by packets following multiple paths through a network, by lower-layer retransmission procedures (such as automatic repeat request), or via parallel processing paths within network equipment that are not designed to ensure that packet ordering is preserved. One of the functions of TCP is to prevent the out-of-order delivery of data, either by reassembling packets in order or requesting retransmission of out-of-order packets.

See also Packet loss Selective ACK IP fragmentation Head-of-line blocking

External links RFC 4737, Packet Reordering Metrics, A. Morton, L. Ciavattone, G. Ramachandran, S. Shalunov, J. Perser, November 2006 RFC 5236, Improved Packet Reordering Metrics, A. Jayasumana, N. Piratla, T. Banka, A. Bare, R. Whitner, June 2008 https://web.archive.org/web/20171022053352/http://kb.pert.geant.net/PERTKB/PacketReordering https://www-iepm.slac.stanford.edu/monitoring/reorder/ https://www.usenix.org/conference/nsdi12/minion-unordered-delivery-wire-compatible-tcp-and-tls

Worked examples

Example 1 — a first encounter with Out-of-order delivery

Start with the simplest possible case. Write down what Out-of-order delivery 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 Out-of-order delivery 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 Out-of-order delivery 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 Out-of-order delivery

In research: Out-of-order delivery 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 Out-of-order delivery 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: Out-of-order delivery is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer network stubs, Packets (information technology), so understanding it makes those chapters shorter.
In everyday life: Look for Out-of-order delivery 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 Out-of-order delivery in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Out-of-order delivery 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 Out-of-order delivery out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Out-of-order delivery in simple terms?

Why does Out-of-order delivery 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 Out-of-order delivery?

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 Out-of-order delivery.