science

Integrated services

Integrated services 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 Integrated services rather than just read about it. In short: In computer networking, integrated services or IntServ is an architecture that specifies the elements to guarantee quality of service (QoS) on networks. IntServ can for example be used to allow video and sound to reach the receiver without interruption.

Key takeaways

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

Reference excerpt

In computer networking, integrated services or IntServ is an architecture that specifies the elements to guarantee quality of service (QoS) on networks. IntServ can for example be used to allow video and sound to reach the receiver without interruption. IntServ specifies a fine-grained QoS system, which is often contrasted with DiffServ's coarse-grained control system. Under IntServ, every router in the system implements IntServ, and every application that requires some kind of QoS guarantee has to make an individual reservation. Flow specs describe what the reservation is for, while RSVP is the underlying mechanism to signal it across the network.

Flow specs There are two parts to a flow spec:

What does the traffic look like? Done in the Traffic SPECification part, also known as TSPEC. What guarantees does it need? Done in the service Request Specification part, also known as RSpec. TSPECs include token bucket algorithm parameters. The idea is that there is a token bucket which slowly fills up with tokens, arriving at a constant rate. Every packet which is sent requires a token, and if there are no tokens, then it cannot be sent. Thus, the rate at which tokens arrive dictates the average rate of traffic flow, while the depth of the bucket dictates how 'bursty' the traffic is allowed to be. TSPECs typically just specify the token rate and the bucket depth. For example, a video with a refresh rate of 75 frames per second, with each frame taking 10 packets, might specify a token rate of 750 Hz, and a bucket depth of only 10. The bucket depth would be sufficient to accommodate the 'burst' associated with sending an entire frame all at once. On the other hand, a conversation would need a lower token rate, but a much higher bucket depth. This is because there are often pauses in conversations, so they can make do with less tokens by not sending the gaps between words and sentences. However, this means the bucket depth needs to be increased to compensate for the traffic being burstier. RSpecs specify what requirements there are for the flow: it can be normal internet 'best effort', in which case no reservation is needed. This setting is likely to be used for webpages, FTP, and similar applications. The 'Controlled Load' setting mirrors the performance of a lightly loaded network: there may be occasional glitches when two people access the same resource by chance, but generally both delay and drop rate are fairly constant at the desired rate. This setting is likely to be used by soft QoS applications. The 'Guaranteed' setting gives an absolutely bounded service, where the delay is promised to never go above a desired amount, and packets never dropped, provided the traffic stays within spec.

RSVP The Resource Reservation Protocol (RSVP) is described in RFC 2205. All machines on the network capable of sending QoS data send a PATH message every 30 seconds, which spreads out through the networks. Those who want to listen to them send a corresponding RESV (short for "Reserve") message which then traces the path backwards to the sender. The RESV message contains the flow specs. The routers between the sender and listener have to decide if they can support the reservation being requested, and, if they cannot, they send a reject message to let the listener know about it. Otherwise, once they accept the reservation they have to carry the traffic. The routers then store the nature of the flow, and also police it. This is all done in soft state, so if nothing is heard for a certain length of time, then the reader will time out and the reservation will be cancelled. This solves the problem if either the sender or the receiver crash or are shut down incorrectly without first cancelling the reservation. The individual routers may, at their option, police the traffic to check that it conforms to the flow specs.

Problems In order for IntServ to work, all routers along the traffic path must support it. Furthermore, many states must be stored in each router. As a result, IntServ works on a small-scale, but as the system scales up to larger networks or the Internet, it becomes resource intensive to track of all of the reservations. One way to solve the scalability problem is by using a multi-level approach, where per-microflow resource reservation (such as resource reservation for individual users) is done in the edge network, while in the core network resources are reserved for aggregate flows only. The routers that lie between these different levels must adjust the amount of aggregate bandwidth reserved from the core network so that the reservation requests for individual flows from the edge network can be better satisfied.

References

External links RFC 1633 - Integrated Services in the Internet Architecture: an Overview RFC 2211 - Specification of the Controlled-Load Network Element Service RFC 2212 - Specification of Guaranteed Quality of Service RFC 2215 - General Characterization Parameters for Integrated Service Network Elements RFC 2205 - Resource ReSerVation Protocol (RSVP) Cisco.com, Cisco Whitepaper about IntServ and DiffServ

Worked examples

Example 1 — a first encounter with Integrated services

Start with the simplest possible case. Write down what Integrated services 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 Integrated services 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 Integrated services 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 Integrated services

In research: Integrated services 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 Integrated services 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: Integrated services is common in secondary-school and first-year university syllabi. It links to neighbouring topics Internet Standards, Internet architecture, Quality of service, so understanding it makes those chapters shorter.
In everyday life: Look for Integrated services 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 Integrated services in 20 minutes

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

Frequently asked questions

What is Integrated services in simple terms?

Why does Integrated services 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 Integrated services?

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 Integrated services.