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What Quality of Service is About

Hanoch Levy

Feb 2003

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Outline

• What is Quality of Service on the Internet about

• What the aims of this workshop

• Structure of the course

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The Users and the service: What Communications Network serve

• User A and User B

• Placed in different locations

• Want to pass data of some type, from one to another.

• Want this to be done good/best/ASAP.

• Want to do it with certain minimal quality requirements.

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The Users and the service: The user point of view

• The single User is at the center of focus

• User is interested in getting the quality / performance it wants

• User does not care a bout other users

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The Scare Resource problem

• Resources are (are’nt?) limited

• Giving the user as much as it needs/ wants may be difficult due to limited resource problem.

• Subjects where there is not resource limitation – do not face Quality of service problem.

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The Scare Resource problem: Does it exist

• Are car-road resources limited? – Definitely, At least at large fractions of the

day.

• Are Network resources limited: – Open question– A debated question– A subjective question: (cost-wise? Indirect-

cost? Damage?)

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Communications Network and QoS :The network angle

• The network serves MANY users

• The network aims at providing good/Best quality to all of its users.

• The network must account for the needs of all users and achieve a mechanism that can meet them.

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Communications Network and QoS :The network angle

• Communications Network is like a set of car roads

• Communication applications are like streams of cars.

• QoS deals with how to operate these roads in order to provide the cars with good quality of service.

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How does it look like: the network from 10K feet

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The User perspective / The application perspective

1. Given the set of traffic rules used by the network user/ application want to:

1. Get the quality it wants (as good as possible, good above certain quality).

2. Pay as little as possible to get that quality.

2. User probably does not care about: 1. Other users (their quality) 2. Fairness to other users.

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The User perspective / The application perspective

1. The application: 1. May care or may not care about other users /

their “fairness”, etc.

2. This depends with what perspective the application was built.

1. Social objective / or :

2. Selfishness

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The eternal race between the network and the users

1. There is an eternal race/game between the network and the users.

1. Network set up rules of operations2. Users try to exploit them 3. Go back to 1.

2. The tighter the rules of operation the less freedom the user has.

3. The tighter the rules of operation the better quality is granted to the users.

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Tightness of operational rules: example1 : Car traffic

1. The Transport (car) system1. Semi loose system

1. One CAN drive 200 KM/Hour2. One Can cross red lights 33 getting better performance one’s car 33 on the account of others.

2. Still rules are strict enough 1. One cannot really do it for long time 2. Where is the looseness:

1. Rules are strict2. Enforcement less strict.

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Tightness of operational rules: example1 : Car traffic

1. Most abuse is on speed / priority at junctions

2. No abuse at volume (bandwidth):1. No limitation on the number of cars one can

buy and send into the street. 2. Reason:

1. Not really necessary2. Car is so expensive – one cannot really send many

cars in.

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Tightness of operational rules: Example2: Telephony

1. The Telephone system 1. Very strict system:

2. User has almost NO CONTROL of how application behaves

3. User has almost no control of the resources she gets from the network

4. User gets VERY GOOD QUALITY

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Tightness of operational rules: Example3: Internet

1. The Internet system1. Quite loose system:

2. Application has some freedom in the traffic it introduces to the network

1. The way it sends the data (later)

3. The user has freedom in how / how much it uses the application:

1. One can send as much email as one wants.

2. One can hit the browser button as hard as one wants.

3. One can down load songs 24 hours a day.

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Objective of this workshop

1. To study and understand the quality of service issues of the Internet.

2. Understand the QoS problems

3. Understand the mechanisms that are used / can be used to provide QOS.

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Methodology and contents of the course

1. Theoretical background – will be provided at class.

2. Practical experience – at the lab.

3. Take the user (“thief”?) perspective: 1. Given the network and the network rules,

client aims at maximizing its performance.

2. What can client do / how should client operate.

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Methodology : Project description

1. You have a client and your objective is to transfer (receive) X files from the network.

2. The files are distributed over N locations. 1. Some may appear in multiple locations.

2. The rate of downloading the files may depend on several parameters, some under your control.

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Methodology : Project description 2

1. Your aim is to download the files to your best satisfaction:

1. As fast as possible

2. At lowest Bandwidth consumption(?)

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Methodology : Project description Part I

1. You are given both the client and the server

2. You aim at building a mechanism (protocol) that will transfer from server to client at maximum “efficiency”

1. Only minimize time 2. Also minimize lost resources (lost packets)

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Methodology : Project description Part II

1. You are given the client only2. K Servers are given and they operate

according to their protocol (FTP)3. Want to download the files efficiently

from the servers1. Only minimize time 2. Also minimize lost resources (lost packets)

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QOS Problems of Interest For network designer

1. Traffic classification and characterization– Properties of traffic – Requirements of the application / traffic– Requirements of the system– Impact on the system

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QOS Problems of Interest (Importance)

1. Traffic classification and characterization– Properties of traffic – Requirements of the application / traffic– Requirements of the system– Impact on the system

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QOS Problems of interest (cont):

2. Policing and shaping– Monitor traffic for obeying the rules – Location: typically at network entrance

3. Node (“Intersection”) design: – Create fast intersections– Introduce mechanisms of prioritization into the

intersections – Guarantee QoS to a traffic stream despite interference

of other streams (fair queuing) – Location: In the nodes

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QOS Problem of interest (cont)

• 4. Do not overflow your nodes (intersections) – estimate node capacity (Call Admission Control)

• 5. Efficient navigation of traffic (Routing) while obeying QoS

• 6. Managing your traffic: Virtual paths (transform your cars into trains…)

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QOS Problem of interest (cont)

• 7. Coordinate through network nodes (reservations): Traffic engineering.

• 8. Traffic characterization.