The document discusses quality of service (QoS) in wireless local area networks (WLANs). It describes the 802.11 medium access control schemes, including distributed coordination function (DCF) and point coordination function (PCF), and their limitations in providing QoS. It then introduces the 802.11e standard, which includes enhanced distributed channel access (EDCA) and HCF controlled channel access (HCCA) to improve QoS support for real-time applications like voice and video.

1. QoS In WLAN
BY
WAQAS SHEHZAD
FAST NU PAKISTAN

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.(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.

5. QoS in TP link wireless router
upload stream
Download

6. IEEE 802.11e
HCF Controlled Channel
Access
Enhanced DCF Channel
Access

7. 802.11 medium access control schemes (MAC).
There are two basic medium
access control (MAC) modes:
 Distributed Coordination
Function (DCF).
 Point Coordination Function
(PCF).

8. 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.

9. 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.

10. Point Coordination Function (PCF)
 Contention free-based.
 Uses a centralized polling scheme.
 Differentiation Considered based on priority.
 Supports synchronous transmission.
.

11. 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.

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

13. 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.

14. EDCA
Priority Access Designation
Category (AC) (Informative)
0 0 Best Effort
1 0 Best Effort
2 0 Best Effort
3 1 Video Probe
4 2 Video
5 2 Video
6 3 Voice
7 3 Voice

15. 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).

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.