computer science

Network tomography

Network tomography 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 Network tomography rather than just read about it. In short: Network tomography is the study of a network's internal characteristics using information derived from end point data. The word tomography is used to link the field, in concept, to other processes that infer the internal characteristics of an object from external observation, as is done in MRI or PET scanning (even though the term tomography strictly refers to imaging by slicing).

Key takeaways

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

Reference excerpt

Network tomography is the study of a network's internal characteristics using information derived from end point data. The word tomography is used to link the field, in concept, to other processes that infer the internal characteristics of an object from external observation, as is done in MRI or PET scanning (even though the term tomography strictly refers to imaging by slicing). The field is a recent development in electrical engineering and computer science, dating from 1996. Network tomography seeks to map the path data takes through the Internet by examining information from “edge nodes,” the computers in which the data are originated and from which they are requested. The field is useful for engineers attempting to develop more efficient computer networks. Data derived from network tomography studies can be used to increase quality of service by limiting link packet loss and increasing routing optimization.

Recent developments There have been many published papers and tools in the area of network tomography, which aim to monitor the health of various links in a network in real-time. These can be classified into loss and delay tomography.

Loss tomography Loss tomography aims to find “lossy” links in a network by sending active “probes” from various vantage points in the network or the Internet.

Delay tomography The area of delay tomography has also attracted attention in the recent past. It aims to find link delays using end-to-end probes sent from vantage points. This can potentially help isolate links with large queueing delays caused by congestion.

More applications Network tomography may be able to infer network topology using end-to-end probes. Topology discovery is a tradeoff between accuracy vs. overhead. With network tomography, the emphasis is to achieve as accurate a picture of the network with minimal overhead. In comparison, other network topology discovery techniques using SNMP or route analytics aim for greater accuracy with less emphasis on overhead reduction. Network tomography may find links which are shared by multiple paths (and can thus become potential bottlenecks in the future). Network Tomography may improve the control of a smart grid

See also Network science Computer network

References

Worked examples

Example 1 — a first encounter with Network tomography

Start with the simplest possible case. Write down what Network tomography 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 Network tomography 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 Network tomography 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 Network tomography

In research: Network tomography 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 Network tomography 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: Network tomography is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrical engineering, Networks, so understanding it makes those chapters shorter.
In everyday life: Look for Network tomography 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 Network tomography in 20 minutes

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

Frequently asked questions

What is Network tomography in simple terms?

Why does Network tomography 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 Network tomography?

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 Network tomography.