Diapositiva 1

1
Performance Comparison of Scheduling Algorithms
for Multimedia Traffic over High-Rate WPANs
A note on the use of these ppt slidesWere
making these slides freely available to all,
hoping they might be of use for researchers
and/or students. Theyre 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
followingIf 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 Thank
s and enjoy!
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_at_dei.unipd.it

presented by Nicola Laurenti
3
Outline

• Introduction
• Traffic types and models
• Polling procedure
• Scheduling algorithms
• Simulation results
• Conclusions

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
5
Objectives and Approach

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

• Paper approach
• focus on classical and well known algorithms
• well established, tested in a great range of
  scenarios, robust and readily portable in the
  novel platform
• knowledge of data requirements, not of data
  types
• we wont focus on narrowed and specialized
  solutions, considering as much heterogeneous
  traffic environments as possible
• fully standard-compliant implementations
• not any improvement/change over the IEEE 802.15.3
  protocol will be proposed, entirely relying on
  standards

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
MAC Management in IEEE 802.15.3
Beacon signaling and information (PNC ?
ALL)? CAP contention period (ALL ? ALL)? CTAP
channel reservation (DEVx ? DEVy,z,)?

• 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

All exchanged data is transported using
conventional frames
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.
9
Multimedia Traffic Models

• MPEG-4
• VBR (extremely high variance)?
• Frame based

HARD DEADLINES

• VoIP
• CBR on/off (VAD)?
• Frame based

MPEG-4 Trace

• Gaming
• VBR
• Random arrivals

SOFT DEADLINES
Gaming Trace
VoIP Model
10
Proposed Polling Procedure

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

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

• Information exchanged at polling time
• Stream ID
• Channel Time Request (CTRq)?
• transmission time requested by in-queue data
• Waited Time
• time already spent in the DEV queue by data

11
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)?

• GPS
• fair scheduling proportionality between
  requests and allocations
• low complexity

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 wont 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
13
Simulation Results (1/3)?
Heterogeneous traffic scenario 5 traffic
profiles and JFRs measured per traffic class

• 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

14
Simulation Results (2/3)?
Heterogeneous traffic scenario mean delay versus
increasing MPEG-4 traffic

• 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.

15
Simulation Results (3/3)?
Heterogeneous traffic scenario JFR versus
increasing MPEG-4 traffic

• Delays are obtained only for successful packets,
  GPS results are then faulty
• Not even for average delay EDF-SH sets results
  apart from -DS

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.