How To Understand Wireless Network Quality Of Service (Qos) In E

Transcription

1 WLAN QoS : e Merle Frédéric

2 Summary Introduction What is QoS? Why do we need QoS in wireless LAN nowadays? e MAC Protocol Enhanced Distributed Channel Access (EDCA) Presentation How does it work? Controlled Channel Access (HCCA) Presentation How does it work? Other specifications Automatic Power Save Delivery Block Acknowledgments NoAck Direct Link Setup Conclusion

3 Introduction

4 What is QoS? Quality of Service (QoS) This is the capacity of the network to provide some kind of functionality Without QoS, when you send some packet on the network, the packet can arrive in any order or take an undefined time to arrive

5 Why we need QoS in wireless LAN nowadays? Evolution of the customer s needs Video and audio streaming Wireless phone over IP Real time applications

6 802.11e This is the standard for WLAN QoS Provide essential services for delaysensitive applications Corresponds to the WMM certification of the WiFi Alliance

7 MAC Protocol Enhanced Distributed Channel Access (EDCA)

8 EDCA Introduction Evolution of Distributed Coordination Function (DCF) Introduces traffic priority Favorite VoIP applications Every hardware with WMM certification supports at least EDCA

9 Main Advancements Introduction of basic traffic priority 4 Types of Traffic Voice Video Best effort Background application Creation of a Transmit Opportunity for each type of traffic

10 How does it work? There is a FIFO stack for each traffic priority High priority traffic waits less than low priority traffic Each traffic priority has a different backoff value The higher the priority, the shorter is the Backoff value

11 How does it work? When a station wins the access, it can send a packet during its Transmit Opportunity (TXOP) The TXOP is different for each priority level The higher the priority, the longer the TXOP

12 MAC Protocol Hybrid Controlled Channel Access (HCCA)

13 HCCA Introduction Evolution of the Point Coordination Function protocol Introduces advanced traffic priority HCCA is the most advanced coordination function HCCA is not mandatory in e There are very few Access Points that implement HCCA nowadays

14 How does it work? Very close to PCF During Contention Period (CP), all stations work in EDCA The Access Point can request a Contention Free Period (CFP) at any time during CP by sending a Control Contention (CC) frame CFP is called Controlled Access Phase (CAP) in e

15 How does it work? During CAP, the Access Point, which is called Hybrid Controller (HC), takes control of the medium Every station sends a Reservation Request frame to request the medium from the HC The HC give access to the medium to a service to send packets during a time defined by the HC

16 Other specifications

17 Automatic Power Save Delivery & Block Acknowledgments Automatic Power Save Delivery (APSD) Advanced power management for VoIP phone. The phone sends and receives data from the Access Point at the same time, and enters a sleep state until more data has to be sent. Block Acknowledgments Block Acknowledgments allow an entire TXOP to be acknowledged in a single frame.

18 NoAck & Direct Link Setup NoAck Asks the receiver not to send an Acknowledgement for that frame. Useful for highly time-critical data Direct Link Setup Allow two wireless devices that are associated to the same AP to directly communicate with each other

19 Conclusion

20 EDCA vs DCF

21 WMM Certification Only EDCA and few options like NoAck are mandatory Two other certifications are needed in order to have the whole HCCA protocol WiFi Scheduled Multimedia WMM-Admission Control

22 References Power Point by Antoine MERCIER about WiFi Power Point from ICARE research laboratory about WLAN QoS Power Point from 3com about WLAN Controller Wikipedia Web site :

23 References WLANs and IP Networking Contributors:Prasad, Neeli; Prasad, Anand Publisher:Artech House, Incorporated Date:2005 ISBN: OFDM for Wireless Communications Systems Contributor:Prasad, Ramjee Publisher:Artech House, Incorporated Date:2004 ISBN: Wireless Internet Telecommunications Contributor:Wong, Daniel Publisher:Artech House, Incorporated Date:2004 ISBN: X