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Internet transit

Internet transit is a 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 Internet transit rather than just read about it. In short: Internet transit is the service of allowing network traffic to cross or "transit" a computer network, usually used to connect a smaller Internet service provider (ISP) to the larger Internet. Technically, it consists of two bundled services: The advertisement of customer routes to other ISPs, thereby soliciting inbound traffic toward the customer from them The advertisement of other ISPs' routes (usually but not nec…

Internet transit — main illustration
Internet transit — illustration

Key takeaways

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

Reference excerpt

Internet transit is the service of allowing network traffic to cross or "transit" a computer network, usually used to connect a smaller Internet service provider (ISP) to the larger Internet. Technically, it consists of two bundled services:

The advertisement of customer routes to other ISPs, thereby soliciting inbound traffic toward the customer from them The advertisement of other ISPs' routes (usually but not necessarily in the form of a default route or a full set of routes to all of the destinations on the Internet) to the ISP's customer, thereby soliciting outbound traffic from the customer towards these networks.

In the 1970s and early 1980s-era Internet, the assumption was made that all networks would provide full transit for one another. In the modern private-sector Internet, two forms of interconnect agreements exist between Internet networks: transit, and peering. Transit is distinct from peering, in which only traffic between the two ISPs and their downstream customers is exchanged and neither ISP can see upstream routes over the peering connection. A transit free network uses only peering; a network that uses only unpaid peering and connects to the whole Internet is considered a Tier 1 network. In the 1990s, the network access point concept provided one form of transit. Pricing for the internet transit varies at different times and geographical locations. The transit service is typically priced per megabit per second per month, and customers are often required to commit to a minimum volume of bandwidth, and usually to a minimum term of service as well, usually using a 95th percentile burstable billing scheme. Some transit agreements provide "service-level agreements" which purport to offer money-back guarantees of performance between the customer's Internet connection and specific points on the Internet, typically major Internet exchange points within a continental geography such as North America. These service level agreements still provide only best-effort delivery since they do not guarantee service the other half of the way, from the Internet exchange point to the final destination.

See also Commercial Internet eXchange (CIX) Federal Internet Exchange (FIX) Internet exchange point (IXP)

References

Illustrations

Internet transit: Diagram of transit (red lines; arrows indicate direction of payment) and peering (green lines) interrelationships between the four types of Autonomous Systems (ASes) of which the Internet is composed. Type 1 networks have "single homed" transit, while type 2 networks have "multi-homed" transit.
Diagram of transit (red lines; arrows indicate direction of payment) and peering (green lines) interrelationships between the four types of Autonomous Systems (ASes) of which the Internet is composed. Type 1 networks have "single homed" transit, while type 2 networks have "multi-homed" transit.

Worked examples

Example 1 — a first encounter with Internet transit

Start with the simplest possible case. Write down what Internet transit claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Internet transit 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 Internet transit 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 Internet transit

In research
Internet transit appears in 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 Internet transit 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
Internet transit is common in secondary-school and first-year university syllabi. It links to neighbouring topics Internet architecture, so understanding it makes those chapters shorter.
In everyday life
Look for Internet transit 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 Internet transit in 20 minutes

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

Frequently asked questions

What is Internet transit in simple terms?

Internet transit is the service of allowing network traffic to cross or "transit" a computer network, usually used to connect a smaller Internet service provider (ISP) to the larger Internet. Technically, it consists of two bundled services: The advertisement of customer routes to other ISPs, there…

Why does Internet transit matter?

Because it connects several 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 Internet transit?

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 Internet transit.

Tags

  • Internet architecture

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