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Claudio Cicconetti, Luciano Lenzini, Enzo Mingozzi, Giovanni Stea

A Software Architecture for Simulating IEEE 802.11e HCCA. Claudio Cicconetti, Luciano Lenzini, Enzo Mingozzi, Giovanni Stea Dipartimento di Ingegneria dell'Informazione University of Pisa, Italy IPS-MoMe 2005 Warsaw, Poland, 14-15 th March 2005. Summary. Introduction

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Claudio Cicconetti, Luciano Lenzini, Enzo Mingozzi, Giovanni Stea

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  1. A Software Architecture for Simulating IEEE 802.11e HCCA Claudio Cicconetti, Luciano Lenzini, Enzo Mingozzi, Giovanni Stea Dipartimento di Ingegneria dell'Informazione University of Pisa, Italy IPS-MoMe 2005 Warsaw, Poland, 14-15th March 2005

  2. Summary • Introduction • Software Architecture • Implementation and preliminary results • Conclusions Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  3. Introduction • New (EuQoS) applications require QoS • videoconference • VoIP • online gaming • ... • The legacy IEEE 802.11 lacks QoS support • Distributed Coordination Function • Point Coordinated Function • Solution: 802.11e • Enhanced Distributed Channel Access (prioritized access) • HCF Controlled Channel Access (parametrized access) Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  4. Legacy 802.11 - DCF • Distributed protocol, based on CSMA/CA: • listen before transmit • collisions detected with positive acknowledgment • binary exponential backoff procedure if collision • All the stations access the medium with the same procedure • Only suitable for best-effort traffic Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  5. Legacy 802.11 - PCF • Contention-Free Periods (CFPs) alternates to Contention-Periods (CPs) at fixed intervals • During CFPs the AP cyclically polls the STAs • Still unsuitable for providing QoS Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  6. 802.11e Enhancements • QoS Access Point (QAP), with • enhanced scheduling capabilities • Admission control • QoS Stations (QSTAs), capable of • Contention-based access • DCF, EDCA • Responding to polls • PCF, HCCA Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  7. 802.11e - EDCA • Distributed protocol • Up to four Access Categories • Based on the differentiation of the CSMA/CA parameters • Achieves relative differentiation of traffic from different ACs • If in infrastructure mode, admission control at the QAP Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  8. 802.11e – HCCA (i) • Centralized • Up to 8 Traffic Streams (TSs) for each QSTA • Traffic specs and requirements (TSPEC) negotiation • Mean data rate, delay bound, etc. • Admission control of TSs at the QAP • Absolute QoS guarantees enforced by scheduling Controlled Access Phases (CAPs) Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  9. HCCA Scheduling • The 802.11e does not define a standard scheduling algorithm at the QAP • A reference scheduler is provided • TDM-like scheduling: TXOP of fixed duration at fixed time intervals for all admitted TSs • Different schedulers are currently being proposed in the literature • We need a common framework for evaluation and testing Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  10. Software Architecture • Modular architecture • MAC fully compliant to the standard HCCA function • MAC functions separated from HCCA scheduling • Allows for flexible integration of various schedulers Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  11. CAP_Hand Has_Control/Lost_Control Transmit Receive/Data_Receive Success MAC (i) • MAC is implemented as a FSM driven by a set of events Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  12. MAC (ii) Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  13. HCCA Scheduler (i) • Listens to a subset of the MAC events • Has_Control/Lost_Control • Possibly others, depending on its actual needs • General interface: • enque(): adds a new packet coming from the LL • deque(): pops the HOL packet • QAP-specific functions • get_next_cap(): returns the expiration time of the next CAP • addTSPEC(): requests the admission of a new TS Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  14. HCCA Scheduler (ii) Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  15. Implementation • The software architecture was implemented in the Network Simulator 2 simulation environment • QAP scheduler: reference 802.11e • QSTA scheduler:FIFO with only one TS Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  16. Preliminary Results (i) • 1 QAP • 3 QSTAs (bidirectional video streaming session) • 3 legacy STAs (asymptotic condition) • 802.11b @ 11 Mbps • Error-free channel • No RTS/CTS, no MAC fragmentation Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  17. Preliminary Results (ii) Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  18. Preliminary Results (iii) Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  19. Conclusions and future work • A software architecture for simulating the IEEE 802.11e HCCA was defined • The scheduling and MAC functions were decoupled by a generic communication interface • The contributed framework has been implemented using ns2 • Future (ongoing) work • Defining, implementing and comparing different HCCA scheduling algorithms for 802.11e Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

  20. End of presentation • Thanks for your attention • ?? || // Dipartimento di Ingegneria dell'Informazione – University of Pisa, ITALY

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