computer science

Network access server

Network access server 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 access server rather than just read about it. In short: A network access server (NAS) is a group of components that provides remote users with a point of access to a network. Overview A NAS concentrates dial-in and dial-out user communications.

Key takeaways

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

Reference excerpt

A network access server (NAS) is a group of components that provides remote users with a point of access to a network.

Overview A NAS concentrates dial-in and dial-out user communications. An access server may have a mixture of analog and digital interfaces and support hundreds of simultaneous users. A NAS consists of a communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. It performs both synchronous and asynchronous routing of supported protocols. The NAS is meant to act as a gateway to guard access to a protected resource. This can be anything from a telephone network, to printers, to the Internet. A client connects to the NAS. The NAS then connects to another resource asking whether the client's supplied credentials are valid. Based on that answer the NAS then allows or disallows access to the protected resource.

Examples The above translates into different implementations for different uses. Here are some examples.

An Internet service provider which provides network access via common modem or modem-like devices (be it PSTN, DSL, cable or GPRS/UMTS) can have one or more NAS (network access server) devices which accept PPP, PPPoE or PPTP connections, checking credentials and recording accounting data via back-end RADIUS servers, and allowing users access through that connection. The captive portal mechanism used by many WiFi providers: a user wants to access the Internet and opens a browser. The NAS detects that the user is not currently authorized to have access to the Internet, so the NAS prompts the user for their username and password. The user supplies them and sends them back to the NAS. The NAS then uses the RADIUS protocol to connect to an AAA server and passes off the username and password. The RADIUS server searches through its resources and finds that the credentials are valid and notifies the NAS that it should grant the access. The NAS then grants the user access to the Internet. Another use of a NAS would be in voice over IP (VoIP). However, instead of using a username and password, many times a phone number or IP Address are used. If the phone number is a valid customer then the call can be completed. Other uses might be to verify whether a phone number has long distance access or a telephone card has minutes left.

Associated protocols Although not required, NASs are almost exclusively used with authentication, authorization, and accounting (AAA) servers. Of the AAA protocols available, RADIUS tends to be the most widely used. The Diameter base protocol extends RADIUS services by providing error handling and inter-domain communications. This protocol is used in networks like the IP Multimedia Subsystem (IMS).

Worked examples

Example 1 — a first encounter with Network access server

Start with the simplest possible case. Write down what Network access server 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 access server 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 access server 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 access server

In research: Network access server 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 access server 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 access server is common in secondary-school and first-year university syllabi. It links to neighbouring topics Network access, Telecommunications infrastructure, Telephony, so understanding it makes those chapters shorter.
In everyday life: Look for Network access server 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 access server in 20 minutes

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

Frequently asked questions

What is Network access server in simple terms?

A network access server (NAS) is a group of components that provides remote users with a point of access to a network. Overview A NAS concentrates dial-in and dial-out user communications.

Why does Network access server 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 access server?

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 access server.