7 May 2008 1

Performance Comparison of Scheduling Algorithms for Multimedia Traffic

over High-Rate WPANsA note on the use of these ppt slides:

We’re making these slides freely available to all, hoping they might be of use for researchers and/or students. They’re in PowerPoint form so you can add, modify, and

delete slides (including this one) and slide content to suit your needs. In return for use, we only ask the following:

If you use these slides (e.g., in a class, presentations, talks and so on) in substantially unaltered form, that you mention their source.

If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors

webpage:

www.dei.unipd.it/~zanella

Thanks and enjoy!

A note on the use of these ppt slides:We’re making these slides freely available to all, hoping they might be of use for

researchers and/or students. They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. In return for use,

we only ask the following:If you use these slides (e.g., in a class, presentations, talks and so on) in substantially

unaltered form, that you mention their source.If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors

webpage:

www.dei.unipd.it/~zanella

Thanks and enjoy!

7 May 2008 2

Performance Comparison of Scheduling Algorithms for Multimedia Traffic

over High-Rate WPANs

Fabio Lorquando, Andrea Zanella

Department of Information Engineering, University of Padova

zanella@dei.unipd.it

presented by Nicola Laurenti

7 May 2008 3

Outline

• Introduction

• Traffic types and models

• Polling procedure

• Scheduling algorithms

• Simulation results

• Conclusions

7 May 2008 4

Introduction

WPAN technologies:

• mobile connectivity among different devices• constant diffusion and adoption increase

The 802.15.3 advance:

• high data rates• strong QoS (Quality of Service) awareness• flexible medium access

Providing intensive multimedia services:

• capable network framework• consciousness of delay bounds• efficient resource management

Careful scheduling policies and design

7 May 2008 5

Objectives and Approach

Paper approach:

• focus on classical and well known algorithmswell established, tested in a great range of scenarios, robust and readily portable in the novel platform

• knowledge of data requirements, not of data typeswe won’t focus on narrowed and specialized solutions, considering as much heterogeneous traffic environments as possible

• fully standard-compliant implementationsnot any improvement/change over the IEEE 802.15.3 protocol will be proposed, entirely relying on standards

Paper objectives:

• investigate IEEE 802.15.3 potentialities in multimedia services• pursue high QoS values in multipurpose WPANs

7 May 2008 6

WPAN IEEE 802.15.3 Basics

Overview:

• ad-hoc network (piconet)

• high bit rate (11 – 55 Mbps)

• centralized by means of a PicoNet Coordinator, PNC

• completely organized in superframe units

• advanced power management

Superframe role:

• piconet management• medium access coordination• medium access differentiation (CSMA/CA, TDMA, ALOHA)

7 May 2008 7

All exchanged data is transported using conventional frames

Through a specific CTRq (Channel Time Request) command frame, any DEV can negotiate a CTAP connection with the PNC. Relevant request parameters are, for example:

• minimal and desired resources per superframe

• traffic type (synchronous or not) and priority

• destination DEVs

MAC Management in IEEE 802.15.3

Beacon – signaling and information(PNC → ALL)

CAP – contention period(ALL ↔ ALL)

CTAP – channel reservation(DEVx → DEVy,z,…)

7 May 2008 8

Soft and Hard Real-Time Processes

Hard real-time processes must obey to hard deadlines. Packets delivered:

• before: represent a success, without discrimination

• after: are unusable and the stream experiences errors

Soft real-time processes set 2 two deadlines: soft and hard. Between them a region extends in which user experience degrades progressively, but data is still meaningful.

7 May 2008 9

MPEG-4MPEG-4:

• VBR (extremely high variance)

• Frame based

VoIPVoIP:

• CBR on/off (VAD)

• Frame based

GamingGaming::

• VBR

• Random arrivals

MPEG-4 Trace

Gaming Trace

HARD DEADLINES

Multimedia Traffic Models

SOFT DEADLINES

VoIP Model

7 May 2008 10

Proposed Polling Procedure

Proposed polling procedure:

• contention free (MCTAs)• managed by the PNC• flexible and efficient• built on 802.15.3 standard

Information exchanged at polling time:

• Stream ID

• Channel Time Request (CTRq)transmission time requested by in-queue data

• Waited Timetime already spent in the DEV queue by data

Stream set-up: upon connection, the DEV transmits its stream soft/hard deadline requirements

7 May 2008 11

GPS:

• fair scheduling: proportionality between requests and allocations

• low complexity

Employed Scheduling Algorithms

Different resource management policies share the same principle: the PNC gathers traffic info from its associated DEVs and executes a scheduling algorithm

We compare 2 main approaches: fair (GPS) and priority based (EDF type)

7 May 2008 12

Employed Scheduling Algorithms

EDF: data closer to theirs deadlines have precedence in channel admittance

Two valuable EDF variations are also considered:

EDF-DS: packets that even so won’t be able to meet their deadlines, are discarded (no channel resources)

EDF-SH: before discarding packets, the scheduler tries to defer access to other streams belonging to a soft real-time process

7 May 2008 13

Heterogeneous traffic scenario: 5 traffic profiles and JFRs measured per traffic class

1

2

3

4

5

0

10

20

30

40

MPEG-4VoIPGAME

Schedulers Results

Traffic Profiles

JFR

[%]

Str

ea

ms/

Pe

ers

GPS

EDF

EDF-DS

MPEG-4

VoIP

GAME

Simulation Results (1/3)

• Remarkable gains with EDF-based schedulers

• Streams with larger frames (as in MPEG-4) greatly benefit of deadline-aware algorithms

• Discard policy may prove valuable particularly in heavily loaded conditions

• VoIP traffic, due to low bit rate and packet size, is not an issue in a CTAP environment

7 May 2008 14

Heterogeneous traffic scenario: mean delay versus increasing MPEG-4 traffic

0 5 10 15 20 25 300

0.5

1

0 5 10 15 20 25 300

0.5

1

0 5 10 15 20 25 300

0.5

1

MPEG-4VoIPGame

Scheduler: GPS

Scheduler: EDF-SH

Scheduler: EDF-DS

JFR

[%]

JFR

[%]

JFR

[%]

JFR

[%]

MPEG-4 Streams

Simulation Results (2/3)

• GPS performs in a proportional fashion

• EFD solutions exhibit a threshold behavior, with excellent QoS until resources are depleted

• With EDF, QoS degradation happens per class of traffic

• EDF-SH solution does not outperform the simpler -DS one.

7 May 2008 15

Heterogeneous traffic scenario: JFR versus increasing MPEG-4 traffic

Simulation Results (3/3)

• Delays are obtained only for successful packets, GPS results are then faulty

• Not even for average delay EDF-SH sets results apart from -DS

0 5 10 15 20 25 300

0.025

0.05

0 5 10 15 20 25 300

0.025

0.05

0 5 10 15 20 25 300

0.025

0.05

MPEG-4VoIPGame

Scheduler: EDF-SH

Scheduler: EDF-DS

Scheduler: GPS

Me

an

De

lay

[s]

Me

an

De

lay

[s]

Me

an

De

lay

[s]

MPEG-4 Streams

7 May 2008 16

Conclusions

In this work we have:

• compared some well known scheduling algorithms

• proposed a standard polling procedure

• simulated piconets with heterogeneous traffic contents

The analysis has shown that:

• as expected, EDF-based schedulers show better performance than GPS-based. This difference is much larger in heterogeneous traffic scenarios than in homogeneous.

• the performance gain obtainable by discarding policies can be relevant

• EDF-SH does not seem to be decisive against the simpler EDF-DS variant

EDF schedulers need to access cross-layer information (i.e. soft/hard stream deadlines). Optimization of polling and signaling might improve results significantly.