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Quality of Service Issues

Network design and security Lecture 12

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Background

Interactive Multimedia (IMM) applications stretch resources What is Quality of service?What does a QoS-aware architecture look like? What building blocks does a QoS-aware architecture consist of?

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ApplicationsFour important properties of multimedia internet broadcasting applications Continuity,

IMM applications generally deliver streams of data Capacity,

Large amounts of data are transported Timeliness

real-time constraints Integrity

presentation constraints

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Architectural consideration

A critical design issue is to provide mechanisms to observe and to control stream continuity, buffer capacities, transmission delays and integrity of data.

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Definition (1)QoS is a system or object property, and consists of a set of quality requirements on the collective behaviour of one or more objects (ISO/IEC IS 10746)for example:

rate of information transfer, the latency, the probability of a communication being

disrupted, the probability of system failure, the probability of storage failure, etc

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Definition(2)

to evaluate the characteristics of a system or service as to its task performance...qualitatively and quantitatively(ETSI)this is an end-user view

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Frameworks(1)

OSI-RM Quality of Service framework ISO 13236 (1997)Covers speed and reliability of transmission - e.g.

throughput, delay, delay variation (jitter), bit error rate (BER), cell loss rate, and connection establishment failure probability etc.

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Frameworks(2)

ODP QoS Framework (1999) More complete than ISO 13236

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ODP framework

QoS management of a system is driven by the QoS characteristics

user requirements or system policies.

A QoS characteristic represents QoS aspects of the system, service or the

resources, the actual behaviour of the application.

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QoS Parameters

Application - mainly presentation characteristics, e.g.

image size resolution, frame rate, start-up delay etc

Transportation - mainly network characteristics e.g

bandwidth, delay, jitter and transmission error rate

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Management Functions(ODP)

Application and Transportation allowing control of QoS

control at transportation level uses congestion detection (i.e after the event)

Control at application level allows for congestion avoidance (before the event)

this split gives a two-level control architecture application and network level

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OthersOther frameworks exist and different groupings used

e.g Nahrstedt uses performance-oriented parameters

e.g. end-to-end delay and bit rate; format-oriented parameters

e.g video resolution, frame rate, storage format and compression scheme

a synchronisation-oriented QoS parameter e.g. the skew between the beginning of audio and

video sequences; cost-oriented parameters

e.g. connection and data transmission charges and copyright fees;

user-oriented parameters these describe the subjective image and sound quality.

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Management functions(ISO)

Stages of evolution of quality-controlled services Prediction resource reservation negotiation monitoring tuning termination

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User’s view

How does this fit with the user’s perception? User’s understand

resolution, image size, colour depth, etc.

Mapped onto communication parameters

cell-loss rate, jitter etc

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QoS Management architecture (de Meer)

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Principles

Basic concepts Feedback (tuning and flow control) Feed-forward (admission control)

Architectures need both to be QoS aware

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CORBA

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TINA

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QoSA - Lancaster

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Heidelberg Architecture

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TENET Architecture

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Omega Architecture

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General featuresResource-oriented mechanisms e.g. point-to-point flow control or

admission control

Openness providing visibility to enable QoS

control e.g filtering shaping, monitoring

Decision procedures to interpret signals for the adaptation

of resources

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Design constraints

To identify openness constraints for a known QoS policy in terms of observability and controllability.

To identify continuous variables that are stringent to the QoS policy to be achieved. Define their relationships to input and output of the system.

To separate, architecturally, control functions from service functions. Define a clear interface between the control plane and the service or network plane.

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Conclusions

Many models existThose outlined are mainly QoS-awareIMM applications will suffer without QoS-awareness