LYU9903
QoS Schemes in Wireless Networks
Ho Pun Mo & Ng Maggie
Supervised by Prof. Lyu R.T. Michael
21 March, 2000
Outline
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Introduction
Review –
What we have done in the last
semester
Preview –
What we will have achieved at the end
of this semester
Current Status
Introduction
Our Targets
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Applying QoS in wireless environment
Video application
Integrating our QoS scheme (wireless)
and LYU9802’s QoS scheme (wired)
Our Difficulties
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QoS in WLAN is a fresh topic
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Must tackle with hardware to achieve good
result
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Few papers/references are available
We have used a few weeks to ponder what we can do
Need to deal with MAC layer
Concern on quality control rather than
producing a product/applying an algorithm!
Must work on a “clean” environment
REVIEW
What we have done in the last semester
Measurement
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Compare the bandwidth usage with and
without QoS
With QoS enabled
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Real-time audio application used more
bandwidths
The mp3 player could play smoothly
Without QoS enabled
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Mp3 player and FTP competed for bandwidths
The mp3 player had “click” sounds
Ported the System to Wireless
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Using LYU9802’s QoS scheme in the
wireless environment and it works! 
Measurement just like the wired one,
except that more time was needed to
play the mp3 and FTP applications
PREVIEW
What we will have achieved at the end
of this semester
Overview of LYU9802’s Scheme
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Component of their QoS Scheme
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Bandwidth Reservation – RSVP
Packet Scheduling – CBQ
Application
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Mp3 player played through wired network
Bandwidth Reservation
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RSVP
Packet Scheduling
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CBQ
QoS Scheme = RSVP + CBQ
Server
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Client
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QoS Scheme for WLAN
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We ain’t focusing on general methods
(It is too harsh! )
Ad-hoc method is used and therefore
assumptions have been taken
Many areas can be improved for the
wireless environment – we will focus on
a specific aspect
For video/audio applications over
WLAN
Schemes We Have Thought Of
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Decrease error rate
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Improve the hand-off mechanism
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Not enough reference! 
Access points must be involved! 
Use a workstation to simulate access
point
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Hardware-oriented! 
Overhead introduced! 
etc.
Scheme We Are Implementing
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What to do?
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In one sentence
Reserving bandwidth before sending
How to do?
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Scenario
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At least two notebooks (with wireless equipment)
An access point connecting to a wired network
A server connecting to the wired network above
Algorithm
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Fact
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Objective
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Packets are burst for real-time applications
Reducing collision probability when real-time
packets are traveling through the air
Method
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Broadcasting a “signal” packet between two
consecutive real-time packets
While receiving the “signal” packet, one would
stop sending packets for a fixed time
Assumptions
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The environment is “clean”
No node will remove from or enter into
the coverage of the access point
Only one real-time client is running
Implementation
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Frame structure
Implementation
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hcf_put_data()
hcf_send()
hcf_get_data()
Video Application
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Purpose
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Demonstration
QoS is embedded!
Design
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Client/server model
Decoder is present on the client side
Video Application
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Implementation Detail
Video Server
MPEG
file
Client
Wired network
Buffer
pipe
mtv
Integration
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Integrating our QoS scheme and
LYU9802’s QoS scheme
LYU9802’s QoS scheme is applied
within the wired network
Our QoS scheme is applied in the
wireless connection
Of course, client is a wireless node
while server is resided in the wired
network
Current Status
Current Status
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Signal packets can be sent
A client/server video application has
implemented (only in wired network,
and QoS is not ready!)
Q&A
Thank You!