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QoS In WLAN

QoS In WLAN. By Abdulbaset Hassan Muneer Bazama. Outline. Introduction QoS Parameters. 802.11 medium access control schemes (MAC). 802.11e medium access control schemes (MAC). Conclusion . Reference. Introduction. What is 802.11?

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QoS In WLAN

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  1. QoS In WLAN By Abdulbaset Hassan Muneer Bazama

  2. Outline • Introduction • QoS Parameters. • 802.11 medium access control schemes (MAC). • 802.11e medium access control schemes (MAC). • Conclusion. • Reference.

  3. Introduction • What is 802.11? • 802.11 refers to a family of specifications developed by the IEEE for wireless LAN technology. • 802.11 Standards. • 1997 - 802.11 up to 2Mbps (900MHZ). • 1999 - 802.11b 2.4GHZ and up to 11Mbps. • 1999 – 802.11a 5GHZ and up to 54Mbps. • 200x – 802.11g 2.4GHZ and up to 54Mbps. • 200x – 802.11e for QoS.

  4. Quality of Service (QoS) • QoS is the capability to provide resource assurance in a network. • QoS Parameters: Bandwidth. Delay. Packet loss rate. Jitter.

  5. 802.11 medium access control schemes (MAC). There are two basic medium access control (MAC) modes: • Distributed Coordination Function (DCF). • Point Coordination Function (PCF).

  6. Distributed Coordination Function (DCF) • Contention-Based. • Based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) algorithm. • Uses a Contention (Backoff) algorithm. • Designed for a best-effort service. • Supports Asynchronous transmission.

  7. B1 = 25 B1 = 5 wait data data wait B2 = 10 B2 = 20 B2 = 15 Example of DCF B1 and B2 are backoff intervals at nodes 1 and 2

  8. Limitation of Distributed Coordination Function (DCF) • Does not provide any QoS guarantees. • Does not support real-time application. • Designed for equal priorities. • Does not support the concept of differentiating frames with different user priorities.

  9. Point Coordination Function (PCF) • Contention free-based. • Uses a centralized polling scheme. • Differentiation Considered based on priority. • Supports synchronous transmission. • Supports time-bounded multimedia applications.

  10. Limitation of Point Coordination Function (PCF) • poor QoS performance. • Uses a simple round-robin algorithm, which can not handle the various QoS requirements. • Transmission time of the polled stations is unknown.

  11. Hybrid Coordination Function (HCF) There are two methods of channel access: • Enhanced DCF channel access (EDCA). • HCF controlled channel access (HCCA).

  12. Enhanced DCF Channel Access (EDCA) • Contention-Based channel access. • Provides service differentiation. • Classifies the traffic into 8 different classes. • Each station has 4 access categories to provide service differentiation.

  13. Pri 0 Backoff (AIFSN0) AC0 Pri 1 Backoff (AIFSN1) AC1 Transmission Attempt Scheduler (resolves virtual collisions by granting TXOP to highest priority 8 User priorities per QSTA 8 User priorities mapping to 4 Access Categories Backoff (AIFSN2) AC2 Backoff (AIFSN3) AC3 Pri 8 EDCA (Cont.) Transmission Opportunity (TXOP): is the time interval permitted for a particular STA to transmit packets.

  14. EDCA (Cont.)

  15. HCF Controlled Channel Access ( HCCA) • Operates in CFP and CP. • Provides Guaranteed Services with a much higher probability than EDCA. • Combines the advantages of PCF and DCF. • Coordinates the traffic in any fashion (not just round- robin).

  16. Conclusion • The IEEE 802.11 wireless LAN (WLAN) has become one of the most widely used wireless technologies in these days. • The 802.11 standards can not provide any QoS guarantees due to poor performance. • The 802.11e offers QoS support to time-sensitive applications, such as, audio and video communications.

  17. References • Paal E. Engelstad and Olav N osterbo, Analysis of QoS in WLAN, Telektronikk 1.2005. (http://folk.uio.no/paalee) • Priyank Garg, Rushabh Doshi, Russell Greene, Mary Baker, Majid Malek, Xiaoyan Cheng, Using IEEE 802.11e MAC for QoS over Wireless, 2003 IEEE. • Jie MaYuan'an Liu,Bihua Tang, QoS Research and Design for WLAN, Proceedings of ISCIT2005. • J.K.Choi, J.S.Park, J.H. Lee, K.S. Ryu, Review on QoS issues in IEEE 802.11 W-LAN, Feb. 20-22, 2006 ICACT2006. • Jose Villalon, Pedro Cuenca and Luis Orozco-Barbosa, Limitations and capabilities of QoSSupport in IEEE 802.11 WLANS, 2005 IEEE. • http://en.wikipedia.org/wiki/IEEE_802.11e.

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