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.(how long it takes for a bit of data to travel across the network from one node or endpoint to another.) Packet loss rate. Jitter.
QoS in TP link wireless routerupload stream Download
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. Designed for a best-effort service. Supports Asynchronous transmission.
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..
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(many users to use the same radio channel without pre-coordination). Provides service differentiation. Classifies the traffic into 8 different classes. Each station has 4 access categories to provide service differentiation.
EDCA Priority Access Designation Category (AC) (Informative)0 0 Best Effort1 0 Best Effort2 0 Best Effort3 1 Video Probe4 2 Video5 2 Video6 3 Voice7 3 Voice
HCF Controlled Channel Access ( HCCA) 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.
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