1 / 60

MAC Enhancements to Support Quality of Service in Wireless Networks

MAC Enhancements to Support Quality of Service in Wireless Networks. Masters Thesis Presentation S.Rajesh AU-KBC Research Centre http://www.au-kbc.org http://www.annauniv.edu Department of Electronics Engineering,

harper
Télécharger la présentation

MAC Enhancements to Support Quality of Service in Wireless Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MAC Enhancements to Support Quality of Service in Wireless Networks Masters Thesis Presentation S.Rajesh AU-KBC Research Centre http://www.au-kbc.org http://www.annauniv.edu Department of Electronics Engineering, Faculty of Information and Communication Engineering, MIT Campus, Anna University, Chromepet, Chennai, TN 600044 INDIA.

  2. Outline • Introduction • MAC for wireless networks • Ad hoc networks • Wireless LAN • Problem Definition • QoS support • Differentiated • Integrated • MAC Enhancements • In ad hoc networks with directional antennas • System model • Results • In WLAN with QoS scheduler • System model • Results • Conclusion S.Rajesh, Anna University

  3. INTRODUCTION Introduction Problem Definition & Contribution MAC Enhancements (Ad hoc / WLAN) System Model (Ad hoc / WLAN) Results (Ad hoc / WLAN) Conclusion

  4. Introduction • WLAN Standard with QoS Enhancement • Basics IEEE 802.11 • QoS enhancements in IEEE 802.11e • HCF • HCF Contention Free Channel Access Mechanism • HCF Contention Based Channel Access Mechanism (EDCF) • (or Enhanced Distributed Coordination Function) • Scheduling Techniques • Prioritized Scheduling for Differentiated and Integrated Traffic • Rate Adaptive Scheduling S.Rajesh, Anna University

  5. Access Point WLAN • Typical Scenarios • Independent BSS • IBSS (Ad hoc mode) • Distributed coordination • Infrastructure BSS • NOT called an IBSS • Central coordination S.Rajesh, Anna University

  6. Access Point Access Point ESS LAN Internet Backbone ESS WLAN BSS BSS S.Rajesh, Anna University

  7. Basic IEEE 802.11 MAC • CSMA/CA • Binary Exponential Back-off • RTS/CTS/Data/ACK handshake • Modes • DCF • Ad Hoc or infrastructureless • PCF • Infrastructure based • Access Point polls the associated stations S.Rajesh, Anna University

  8. DCF D S S S D N ST S S R DATA T S 1 NAV (RTS from 3) C A C T C T S K S 2 R DATA T S 3 NAV (RTS from 1) D S S S D BkOff S S time à 802.11a parameters m S SIFS (Short Inter Frame Space) 16 s à m D DIFS (DCF Inter Frame Space) 34 s à m ST Slot Time for each Back-off counter 9 s à S.Rajesh, Anna University

  9. DCF • Beacon • generated by any of the nodes in the IBSS • MPDU transmission • If channel is free for a DIFS transmit (RTS,…, Data,...) • else • wait till it becomes free for a DIFS • generate random backoff slot-times in (0-Cwmin) • if channel is free count down one slot time • else freeze and resume countdown • the channel becomes free for a DIFS • on reaching zero transmit • if failed retry from first step (for max retries (7) times) S.Rajesh, Anna University

  10. Contention Free Repetition Interval Contention Free Period Contention period SIFS SIFS SIFS PIFS SIFS SIFS DIFS +BK SIFS SIFS SIFS Beacon Data & CF Poll to 1 CF Poll to 2 & Ack to 1 CF Poll to 3 CF End PC NAV M1 NAV M2 Dead NAV M3 NAV M4,5 IBSS NAV Set by Beacon Cleared by CF End Data from 1 &CF Ack Set by Beacon Cleared by CF End CF Ack Set by Beacon Cleared by CF End R T S C T S Data A c k Set by RTS Time --> PCF S.Rajesh, Anna University

  11. PCF • Beacon • always generated by the AP • Transmission • AP transmits Multicast/Broadcast data first • AP transmits data to associated stations one by one and along with that it polls these stations to send data if any in contention free mode • If the station doesn’t respond within PIFS, the AP gets the channel with better chance as PIFS<DIFS • After CFPmaxduration channel is left for contention based access • Contention Free Period and Contention Period alternate S.Rajesh, Anna University

  12. HCF Contention Free Repetition Interval Contention Free Period Contention period SIFS SIFS SIFS PIFS SIFS SIFS AIFS+BK SIFS SIFS SIFS Beacon Data & CF Poll to 1 CF Poll to 2 & Ack to 1 CF Poll to 3 CF End PC NAV M1 NAV M2 Dead NAV M3 NAV M4,5 IBSS NAV Set by Beacon Reserved by TXOP Reserved by TXOP Cleared by CF End Reserved by TXOP Data from 1 &CF Ack Set by Beacon Reserved by TXOP Reserved by TXOP Cleared by CF End CF Ack Set by Beacon Reserved by TXOP Reserved by TXOP Cleared by CF End R T S C T S Data A c k Set by RTS Time --> S.Rajesh, Anna University

  13. EDCF Queuing S.Rajesh, Anna University

  14. AIFS S.Rajesh, Anna University

  15. Problem Definition and Contribution Introduction Problem Definition & Contribution MAC Enhancements (Ad hoc / WLAN) System Model (Ad hoc / WLAN) Results (Ad hoc / WLAN) Conclusion

  16. Problem Definition • Link level QoS support in • Ad hoc networks • WLANs • Differentiated • Access Category based • Integrated • Guaranteed QoS S.Rajesh, Anna University

  17. Contribution • MAC enhancements to support QoS • In ad hoc networks • Using directionality of the directional antenna • Using intermittent immobile nodes • Using direction aware scheduler • In WLAN • Using estimation based • Scheduler linked with • Traffic shaping and policing • Admission Control S.Rajesh, Anna University

  18. MAC Enhancements in Ad hoc Networks Introduction Problem Definition and Contribution MAC Enhancements (Ad hoc Networks) System Model (Ad hoc / WLAN) Results (Ad hoc / WLAN) Conclusion

  19. Solution - Structuring • Ad hoc networks • Structural aspects: • topology free, infrastructure independent • Functional aspects: • multi-hop, common frequency band for all nodes, no central coordination • More overhead / expense on: • routing, MAC, power consumption • due to • highly dynamic state and random state transitions, distributed coordination S.Rajesh, Anna University

  20. Disconnected Clusters Stray Nodes Bottle Necks Ad hoc Network - Challenges S.Rajesh, Anna University

  21. Enhancements • Use • interspersed stationary nodes • to reduce probability of any region getting void of even a single node to connect with • directional antenna in these nodes • to improve range (without power-back-off) • to improve frequency reuse (with power-back-off) • smart directionality scheduler • to help high priority node(s) or traffic to gain access • to prevent starvation of lower priority node(s) or traffic S.Rajesh, Anna University

  22. Disconnected Clusters: Various beam shapes of Directional nodes can form an underlying infrastructure Stray Nodes: High priority far off nodes can be reached with long beam Bottle Necks: Providing more buffers at the strategically placed directional nodes … contd … S.Rajesh, Anna University

  23. System Model Ad hoc Networks Introduction Problem Definition and Contribution MAC Enhancements (Ad hoc / WLAN) System Model (Ad hoc Networks) Results (Ad hoc / WLAN) Conclusion

  24. Antenna Patterns • Omni-directional • Directional Antenna • Beam • single • multi • Power • same as omni-directional • backed-off / increased S.Rajesh, Anna University

  25. Omni-directional (e.g.: RTS/CTS/Data/Ack, CSMA/CA as in DCF of IEEE 802.11) Directional Static directionality based on node distribution where node density is more need for bridging or relaying Dynamic directionality based on (source, destination) pairs Traffic Traffic intensity for uniform traffic Traffic category MAC Based on Antenna S.Rajesh, Anna University

  26. State diagram of enhanced MAC S.Rajesh, Anna University

  27. Results in • Improved connectivity • Improved QoS S.Rajesh, Anna University

  28. Connectivity Improvement with Stationary Nodes • Probability • that two mobile nodes contact at single hop • that a mobile and a immobile node contact at single hop • Improvement factor in contact probability S.Rajesh, Anna University

  29. Connectivity Improvement with Directional Nodes • Coverage radius • Romni = 100m • Rdirectional = 500m • Rnetwork = 1000m • Single hop probability with • Omni-directional nodes • 1002/10002 = 1/100 • Directional nodes • 5002/10002 = 1/4 • Improvement factor52 or (Romni/Rdirectional)2 S.Rajesh, Anna University

  30. Traffic Intensity Calculation S.Rajesh, Anna University

  31. Traffic Based Direction Scheduling for Better QoS pis the priority weight of the corresponding traffic class S.Rajesh, Anna University

  32. Scenario • All mobile case • With intermittent mobile nodes • without directional antennas • with directional antennas • with smart traffic-intensity based scheduling • with smart traffic-category based scheduling S.Rajesh, Anna University

  33. Network Diameter Antenna Pattern Omni-directional: radius Directional beam width (lower limit) range (upper limit) Access Method Routing Technique 2000m 100m 2/6.25 for reaching 250m with same power 802.11 MAC CSMA/CA RTS/CTS/Data/ACK Shortest Path Simulation Parameters S.Rajesh, Anna University

  34. …Contd...Simulation Parameters Less Delay sensitive More Delay sensitive Non Preemptive scheduling Preemptive scheduling FCFS Scheduler S.Rajesh, Anna University

  35. Results Introduction Problem Definition and Contribution MAC Enhancements (Ad hoc / WLAN) System Model (Ad hoc / WLAN) Results (Ad hoc Networks) Conclusion

  36. Throughput Performance S.Rajesh, Anna University

  37. Delay Performance S.Rajesh, Anna University

  38. MAC Enhancements in WLANs Introduction Problem Definition and Contribution MAC Enhancements (WLANS) System Model (Ad hoc / WLAN) Results (Ad hoc / WLAN) Conclusion

  39. Solution Structuring • To design a common scheduler • that can handle both • (a) Contention free traffic and • (b) Contention based traffic • or • (1) Traffic with resource reservation and • (2) Traffic without resource reservation • Though not necessary, (1) is handled using (a) and (2) using (b). • Exceptionally some bursts are allowed for (1) in (b) also called CFB or Contention Free Bursts S.Rajesh, Anna University

  40. System - Block Diagram S.Rajesh, Anna University

  41. Traffic Flow • Traffic Classification • Traffic corresponding to declared Traffic Streams (TSs) • Shaped and Policed using Twin Token Bucket • Sent as per TS scheduler in HCF • Traffic not associated with Traffic Streams (TSs) • RED queue mechanism used • Sent as per EDCF budget declared by HC in HCF S.Rajesh, Anna University

  42. Twin Token Bucket • Traffic • Shaping • Policing Bucket 1 Bucket 2 Token filling rate (Constant) r1 = Peak Data Rate r2 = Mean Data Rate Bucket Size s1 = 1 token (mimic leaky bucket) s2 = Maximum Burst Size tokens Token extraction rate - At most Peak Data Rate Major purpose Rate limiting Burst size limiting S.Rajesh, Anna University

  43. Scheduling Based on Packet Error Information • Scheduler schedules and admits Traffic Streams based on effective bandwidth • Effective Mean Data Rate (EMDR) • control factor n is varied based on observed packet errors S.Rajesh, Anna University

  44. EMDR estimate = 54/(1+e-n) • n = n-1 + x • where, • x= 1 if successful, -1 if unsuccessful • In implementation • n ranging to infinity can not be realized, • n should itself adapt based on channel condition • So, n is • upper limited to +/- 127 • replaced by ’ which is a function of deviation in n S.Rajesh, Anna University

  45. Aggregate the mean and peak data rate requirements mentioned through TSPEC for each admitted TS • Set rate of token filling in second bucket in Twin Token bucket , r2 to max(Estimated EMDR, algebraic sum of mean data rates of admitted TSs) S.Rajesh, Anna University

  46. Admission Policy • Admit Traffic Streams until aggregate mean data rate of existing traffic streams does not exceed EMDR, • (reject otherwise). • Bandwidth not used for TS is allocated through EDCF budget for Contention based access S.Rajesh, Anna University

  47. Scheduling Based on Rate Adaptation Information • Typically multiple rates are allowed • 54, 48, 36, 24, 18,12, 9, 6 Mbps • Rate adaptation is done based RSSI or other techniques • n = n-1 + x’ • where, x’ = x*(54*106)/r • where, • x= 1 if successful, -1 if unsuccessful • and • r is the rate of transmission of previous packet S.Rajesh, Anna University

  48. …Contd...Simulation Parameters Less Delay sensitive More Delay sensitive Non Preemptive scheduling Preemptive scheduling FCFS Scheduler S.Rajesh, Anna University

  49. Results Introduction Problem Definition and Contribution MAC Enhancements (Ad hoc / WLAN) System Model (Ad hoc / WLAN) Results (WLAN) Conclusion

  50. Goodput of EDCF S.Rajesh, Anna University

More Related