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Vijay_ICCN-11

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Vijay_ICCN-11

  1. 1. Improved QoS in WLAN Using IEEE 802.11e Vijay B T Ph.D. Student Department of Electronics and Communication Engineering National Institute of Technology Tiruchirappalli India Under supervision of Dr. B Malarkodi, Assoc. Professor NITT-15 August 20, 2016 Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 1 / 35
  2. 2. Overview 1 Objectives 2 Simulation Methodology 3 Reverbed Modeler 4 Motivation 5 Basic IEEE 802.11 IEEE 802.11 Logical Architecture MAC Protocol Functionality MAC for Channel Access Functions 6 IEEE 802.11e MAC Layer Modified MAC Architecture HCF - Inception Transmission Opportunity (TXOP) HCF Controlled Access 7 Simulation Results 8 Conclusion and Future Enhancement 9 References Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 2 / 35
  3. 3. Objectives Objectives Cutting edge mechanisms for QoS assistance, specifically Enhanced Distributed Coordination Function (EDCF) and Hybrid Coordination Function (HCF), defined within the 802.11e drafts are usually evaluated. Pre-eminent Objectives are as follows: Reducing the number of retransmission attempts by providing very good service differentiation. Medium Access delay improved by adding management frames. To minimizing the Data dropped due to unavailability of access to medium. Increase the Throughput of the Network by reordering relative Priorities. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 3 / 35
  4. 4. Simulation Methodology Simulation Methodology The below figure shows a system of methods used in a particular Reverbed Modeler [AE 17.5 PL6] to study of IEEE 802.11e. Figure: Flow Diagram Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 4 / 35
  5. 5. Reverbed Modeler Reverbed Modeler[AE 17.5 PL6] This scenario studies impact of deploying 802.11e QoS facilities on network performance, where stations generating application traffic for all QoS (ToS) classes are present. Figure: Study of IEEE 802.11e [4] It also highlights how a QAP (11-e capable access point) can overwrite the EDCA Parameters for each Access Category to re-order their relative priorities. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 5 / 35
  6. 6. Reverbed Modeler The Project/Scenario Workflow Create Project Create baseline Scenario Import or create topology Import or create traffic Choose results and reports to be collected Run simulation View results Duplicate Scenario Make Changes Re-run Simulation Compare results Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 6 / 35
  7. 7. Reverbed Modeler 3-Tired Reverbed Modeler Hierarchy Three domains: network, node, and process Node model specifies object in network domain Process model specifies object in node domain Figure: 3-Tired Hierarchy Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 7 / 35
  8. 8. Reverbed Modeler Object Attributes Here we can do what ever we want like changing routing parameters, MANET Properties or WLAN Configuration and ... All objects have attributes that control aspects of their behaviors and attributes may vary from one model to the next Attribute values may vary between objects of the same model type Right-click on an object and select “Edit Attributes” to view or change its attributes Figure: Edit Attributes Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 8 / 35
  9. 9. Motivation Motivation Customary The IEEE 802.11 WLAN is being deployed widely and rapidly for many different environments including enterprise, home, and public access networking. Feature The main characteristics of the 802.11 standard are simplicity and robustness against failures due to the distributed approach of its MAC protocol. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 9 / 35
  10. 10. Basic IEEE 802.11 Basic IEEE 802.11 The following features of Basic IEEE 802.11 are ... A basic standard for WLAN Comprise of several component and services and provides station mobility Supports network topologies such as BSS, EBSS and IBSS. Has three different PHY layers: DSSS in 2.4 GHz band, FHSS in 2.4 GHz band, IR light Supports CSMA/CA access method Support of Privacy and security of data being transferred. Support data rates of I Mbps to 2 Mbps. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 10 / 35
  11. 11. Basic IEEE 802.11 IEEE 802.11 Logical Architecture IEEE 802.11 Logical Architecture The logical architecture defines the network’s operation, which applies to each station consists of a single MAC and one of multiple PHYs Figure: IEEE 802.11 entities The goal of the MAC layer is to provide access control functions for shared-medium PHYs in support of the LLC layer. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 11 / 35
  12. 12. Basic IEEE 802.11 MAC Protocol Functionality MAC Protocol Functionality The main purpose of MAC layer is to 1 Provide data services to the user of MAC i.e. higher layer protocols. 2 Control fair access to the shared wireless medium To understand these functionalities, we consider Basic Service Set (BSS) composed of an Access Point (AP) and a number of stations associated with AP. Standard defines two methods 1 Frame Exchange Protocol 2 RTS/CTS Mechanism (Optional) This mechanism is defined to increase the robustness of the protocol and address problems such as hidden node. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 12 / 35
  13. 13. Basic IEEE 802.11 MAC for Channel Access Functions MAC for Channel Access Functions Standard specifies two Channel Access Functions DCF (Distributed Coordination Function) 1 Basic access method, mandatory for all STAs 2 Allows sharing of wireless medium between compatible PHY layer devices through use of CSMA/CA PCF (Point Coordination Function) 1 Its for controlled access 2 An optional channel access function is designed to support time bounded services. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 13 / 35
  14. 14. Basic IEEE 802.11 MAC for Channel Access Functions Inter Frame Spacing 802.11 MAC protocol are given while values for different IFS are given in Table SIFS = Short inter frame space = as in Table dependent on PHY PIFS = point coordination function (PCF) inter frame space = SIFS + slot time DIFS = distributed coordination function (DCF) inter frame space = PIFS + slot time the back-off timer is expressed in terms of number of time slots. PHY SIFS DIFS Slot time CWmin 802.11a 16 34 9 15 802.11b 10 50 20 31 802.11g 10 50 20 15 Table: MAC values in microseconds for different PHYs [3] Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 14 / 35
  15. 15. Basic IEEE 802.11 MAC for Channel Access Functions Coexistence of PCF and DCF In the case of DCF Carrier Sense is performed using both Physical and Virtual Mechanism Figure: Coexistence of PCF and DCF Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 15 / 35
  16. 16. Basic IEEE 802.11 MAC for Channel Access Functions PCF It is for controlled access to medium Its an optional channel access function and is designed to support time bounded services. Contention free access to the wireless medium is controlled by Point Coordinator collocated with the AP. IEEE 802.11 defines two periods between two consecutive Delivery Traffic Indication Msgs (DTIM) and beacons Contention Period (CP) Contention Free Period (CFP) Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 16 / 35
  17. 17. Basic IEEE 802.11 MAC for Channel Access Functions PCF-Polling Polling Polling starts by PC sending a CF-Poll frame to one of pollable STAs. If the PC itself has pending transmission it could use data frame piggybacking CF-Poll frame. The polled STA can respond with Data + CF-Ack frame or with CF-Ack only, if there is no pending transmission in STA. Once the frame sequence with one station is complete, PC sends CF-Poll to another STA in its list of Pollable STA. When PC has finished polling all pollable STAs, or CFP duration has expired, PC broadcasts a CF-end frame to announce the end of CFP. The NAV of all STAs are set to maximum at TBTT to protect CFP from unwanted transmission. Then the AP broadcast the actual CFP duration in the beacon, and NAV are updated accordingly. At the end of CFP, all STAs reset, their NAV to zero, when either they have received CF-End frame or CFP duration expires. From now on until the next DTIM beacon, all STAs contend for wireless medium using DCF. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 17 / 35
  18. 18. IEEE 802.11e MAC Layer IEEE 802.11e MAC Layer The major enhancement of 802.11e Traffic differentiation Concept of Transmission Opportunity (TXOP) Enhanced DCF (contention-based) HCP controlled channel access (contention free) Burst ACK (optional)⇒ Not Explore Here Direct link protocol (DLP)⇒ Not Explore Here Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 18 / 35
  19. 19. IEEE 802.11e MAC Layer Modified MAC Architecture Modified MAC Architecture Hybrid Coordination Function (HCF)⇒ IEEE 802.11 Task Group E (TGe) proposes HCF to provide QoS for real-time applications. DCF ⇒ A contention-base access for 802.11. PCF ⇒ An option to support contention-free access in 802.11. [1] Figure: Upgrade MAC Architecture Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 19 / 35
  20. 20. IEEE 802.11e MAC Layer HCF - Inception HCF - Inception HCF combines functions from the DCF and PCF with enhanced QoS-specific mechanisms. HCF consists of Enhance DCF (EDCF) for contention-based access Controlled Access (HCCA) for contention-free access Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 20 / 35
  21. 21. IEEE 802.11e MAC Layer HCF - Inception HCF - Interpretation (1/2) Interpretation with respect to Modified MAC Architecture Hybrid coordinator (HC) The point coordinator for HCF. QoS access point (QAP) An access point (AP) that implements the access point functions specified in the IEEE 802.11e standard. QoS facility The set of enhanced functions, frame exchange sequences, and management objects. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 21 / 35
  22. 22. IEEE 802.11e MAC Layer HCF - Inception HCF - Interpretation (2/2) Interpretation with respect to Modified MAC Architecture QoS station (QSTA) An IEEE 802.11 station which implements QoS facility and HCF. QoS basic service set (QBSS) A basic service set that supports QoS facility specified in the IEEE 802.11e. QoS independent basic service set (QIBSS) An independent basic service set in which one or more of its stations support the QoS facility. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 22 / 35
  23. 23. IEEE 802.11e MAC Layer HCF - Inception EDCF – Traffic Category The EDCF provides differentiated access to the WM for 8 priorities, identical to IEEE 802.1D priority tag, for non-AP STAs. Priorities are numbered from 0 (the lowest priority) to 7 (the highest priority). The set of MSDUs with the same priority is refer to a Traffic Category (TC). Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 23 / 35
  24. 24. IEEE 802.11e MAC Layer HCF - Inception EDCF - Access Category (1/4) EDCF defines access category (AC) mechanism to support the priority mechanism at the non-AP QSTAs. An AC is an enhanced variant of the DCF which contends for transmission opportunity (TXOP) using the set of parameters such as CWmin[AC], CWmax[AC], AIFS[AC], etc. The parameter set is specified in the “EDCA parameter set element” of beacon frames.[2] AC CWmin CWmax AIFS 0 CWmin CWmax 2 1 CWmin CWmax 1 2 (CWmin + 1)/2 - 1 CWmin 1 3 (CWmin + 1)/4 - 1 (CWmin + 1)/2 - 1 1 Table: Default QoS Parameter set Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 24 / 35
  25. 25. IEEE 802.11e MAC Layer HCF - Inception EDCF - Access Category Timing Diagram (2/4) The timing relationship for an EDCF is shown in Figure Figure: Timing Diagram Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 25 / 35
  26. 26. IEEE 802.11e MAC Layer HCF - Inception EDCF - Access Category (3/4) Virtual Contention with in a station is shown below figure An QSTA has four ACs. Collision between ACs within a QSTA is called internal collision. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 26 / 35
  27. 27. IEEE 802.11e MAC Layer HCF - Inception EDCF - Access Category (4/4) Internal collision resolution: High priority AC wins the right of transmission, but low priority AC back off as if it experiences a collision. The mapping from 8 priories to 4 ACs are : User Priority AC Traffic Type 1 0 (BK) Background (BK) 2 0 (BK) Spare or Standard 0 1 (BE) Best Effort (BE) 3 1 (BE) Excellent Effort (EE) 4 2 (VI/AVI) Controlled Load (CL) 5 2 (VI) Video < 100ms latency (VI) 6 3 (VO) Voice < 10ms latency (VO) 7 3 (VO/AVO) Network Control (NC) Table: Mapping Virtual Contention Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 27 / 35
  28. 28. IEEE 802.11e MAC Layer Transmission Opportunity (TXOP) Transmission Opportunity (TXOP) Definition : which enables a station to transmit multiple frames consecutively within a burst after it gains the channel. A TXOP is defined by a starting time and a maximum duration. Two types of TXOP: EDCF TXOP and Polled TXOP. An EDCF TXOP begins when the wireless medium is determined to be available under the EDCF rules, and the length of TXOP is specified in beacon frames. An Polled TXOP begins when a QSTA receives a QoS(+)CF-Poll from HC, and the length of TXOP is specified in the QoS(+)CF-Poll. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 28 / 35
  29. 29. IEEE 802.11e MAC Layer HCF Controlled Access HCF Controlled Access Differences between hybrid coordinator (HC) and point coordinator (PC): HC can poll QSTAs in both CP and CFP HC grants a polled TXOP to one QSTA, which restricts the duration of the QSTA’s access to the medium. Figure: Timing Diagram Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 29 / 35
  30. 30. Simulation Results Simulation Results WLAN Delay (1/3) The WLAN end-to-end delay values measured by STAs Voice-1, Video-1 Best Effort-1 and Background-1 are compared. When all STAs belong to BSS-1, each reports similar end-to-end delays. Figure: WLAN Delay Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 30 / 35
  31. 31. Simulation Results Simulation Results WLAN AP Connectivity (2/3) When the mobile STAs roam with BSS-1 to BSS-2, they can be now make use of EDCA to contend for the medium since their current AP is often a QAP. Prioritized solution for the higher-layer traffic straight away impacts on the measured delay values. Figure: WLAN AP Connectivity Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 31 / 35
  32. 32. Simulation Results Simulation Results WLAN Throughput (3/3) VI AC reports throughput only starting around 250 seconds in the simulation QSTAs handle all higher layer traffic along with all traffic received from the medium as BE traffic. Figure: WLAN Throughput Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 32 / 35
  33. 33. Conclusion and Future Enhancement Conclusion and Future Enhancement Choosing the concept of varying levels of services for different traffic types, i.e. voice, video and data. Which often supports a unique priority to access the radio channel. Fidelity and Flexibility of IEEE 802.11e QoS mechanisms. Future Enhancement A couple changes to IEEE 802.11 have recently been published 802.11aa and 802.11ae.By providing support for multicast transmission, improved audio video streaming, coping with inter-network interference, and better prioritization of management frames. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 33 / 35
  34. 34. References References Katarzyna Kosek-Szott, Marek Natkaniec, and Szymon Szott What’s New for QoS in IEEE 802.11? Journal of IEEE Network, 2(1):95–104, 2013. Mangold, Stefan and Choi et al., Analysis of IEEE 802.11 e for QoS support in wireless LANs IEEE Wireless Communications, 10(6):40–50, 2003. Daqing Gu and JinyunZhana, QoS Enhancement in IEEE 802.11 Wireless Local Area Networks IEEE Communication Magazine,41(6): 120–124, 2003 Adarshpal S. sethi , Vasil Y. Hnatyshin. The Practical OPNET User Guide for Computer Network Simulation. CRC press Taylor and Franscis Group, 2011. Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 34 / 35
  35. 35. References The End Any Questions! Thank You Vijay B T (NITT) ICCN - 11 (MAC Layer Protocol) August 20, 2016 35 / 35

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