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QoS In WLAN

Outline

IntroductionQoS 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 router

upload stream

Download

IEEE 802.11e

HCF Controlled Channel Access

Enhanced DCF Channel Access

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 Category (AC)

Designation (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

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.