Presentation on theme: "QoS In WLAN By Abdulbaset Hassan Muneer Bazama. Outline Introduction QoS Parameters. 802.11 medium access control schemes (MAC). 802.11e medium access."— Presentation transcript:
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? 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.
Quality of Service (QoS) QoS is the capability to provide resource assurance in a network. QoS Parameters: Bandwidth. Delay. Packet loss rate. Jitter.
802.11 medium access control schemes (MAC). There are two basic medium access control (MAC) modes: Distributed Coordination Function (DCF). Point Coordination Function (PCF).
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.
Example of DCF B1 and B2 are backoff intervals at nodes 1 and 2 data wait B1 = 5 B2 = 15 B1 = 25 B2 = 20 data wait B2 = 10
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.
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.
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.
Hybrid Coordination Function (HCF) There are two methods of channel access: Enhanced DCF channel access (EDCA). HCF controlled channel access (HCCA).
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.
EDCA (Cont.) 8 User priorities mapping to 4 Access Categories Scheduler (resolves virtual collisions by granting TXOP to highest priority 8 User priorities per QSTA Pri 0 Pri 1 Pri 8 Backoff (AIFSN3) Backoff (AIFSN2) Backoff (AIFSN1) Backoff (AIFSN0) AC0 AC1 AC2 AC3 Transmission Attempt Transmission Opportunity (TXOP): is the time interval permitted for a particular STA to transmit packets.
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).
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.
References 1.Paal E. Engelstad and Olav N osterbo, Analysis of QoS in WLAN, Telektronikk 1.2005. (http://folk.uio.no/paalee)http://folk.uio.no/paalee 2.Priyank Garg, Rushabh Doshi, Russell Greene, Mary Baker, Majid Malek, Xiaoyan Cheng, Using IEEE 802.11e MAC for QoS over Wireless, 2003 IEEE. 3.Jie MaYuan'an Liu,Bihua Tang, QoS Research and Design for WLAN, Proceedings of ISCIT2005. 4.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. 5.Jose Villalon, Pedro Cuenca and Luis Orozco-Barbosa, Limitations and capabilities of QoSSupport in IEEE 802.11 WLANS, 2005 IEEE. 6.http://en.wikipedia.org/wiki/IEEE_802.11e.