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Université de Nice Sophia-Antipolis Ecole Doctorale STIC DEA Réseaux et Systèmes Distribués. Adaptive Channel allocation for QoS Enhancement in IEEE 802.11 Wireless LANs. Presented by: Mohammad Malli. Advisors: Qiang Ni, Thierry Turletti, and Chadi Barakat.

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slide1

Université de Nice Sophia-Antipolis

Ecole Doctorale STIC

DEA Réseaux et Systèmes Distribués

Adaptive Channel allocation for QoS

Enhancement in IEEE 802.11 Wireless LANs

Presented by:Mohammad Malli

Advisors:Qiang Ni, Thierry Turletti, and Chadi Barakat

PLANETE group, INRIA Sophia-AntipolisJuly 1, 2003

outline
Outline
  • IEEE 802.11 and 802.11e
  • Problems and Solutions
  • Simulation Topologies and Parameters
  • Our scheme: Adaptive EDCF
  • Our scheme: Adaptive DCF
  • Conclusions and Future Work

July 1, 2003

ieee 802 11
IEEE 802.11

New technology

  • Provide end-users the benefits of increased mobility & productivity
  • Enable network connectivity at locations where cabling is either difficult or costly to install

IEEE 802.2

Logical Link Control (LLC)

IEEE 802.11

Media Access Control (MAC)

IEEE 802.11 Physical Layer

(FHSS, DSSS, IR)

July 1, 2003

ieee 802 11 mac
IEEE 802.11 MAC

MAC layer uses twokinds of protocols to access to the medium

  • DCF : Distributed Coordination Function is used to

support asynchronous data transmissions

  • PCF: Point Coordination Function is designed for

time-bounded multimedia applications

July 1, 2003

slide5

CSMA/CA

Data

Data

Time

Source

SIFS

Ack

Destination

DIFS

Backoff Time

Others

Defer Access

Backoff_Time = Rand(0, CW) * aSlotTime

Backoff Counter must be decreased each slot time by one slot time whenever the channel is idle

  • CW is initially set to CWmin
  • CW is doubled after a failed transmission
  • CW is set to Cwmin, when the packet is successfully transmitted

July 1, 2003

dcf limitations
DCF Limitations

DCF is unsuitable for real time applications because it doesn’t support service differentiation

DCF suffers from significant throughput degradation and high delay at high load due to high collision rate and wasted number of idle slots in each backoff contention cycle

Collisions

DIFS

DIFS

SIFS

ACK

DIFS

SIFS

ACK

DIFS

Virtual transmission time

Idle backoff slots (at each contention period)

July 1, 2003

slide7

FCR (Fast Collision Resolution)

  • Proposed by Florida U. (Infocom ’03)
  • Extends the basic DCF (no service differentiation), to improve the

throughput

  • Main features:

- Static Backoff Threshold value = 2 * (CWmin + 1) - 1

- Increasing CW when the channel is busy during deferring periods

  • Weakness:
  • Backoff Threshold must be adapted to the medium state because during high load, the period of exponential state must be shorter to reduce aggressivity
  • When the channel is busy, it is better that the node waits with its remaining backoff time because doubling the CW during deferring periods increases the number of idle slots in low and medium load cases

July 1, 2003

ieee 802 11e
IEEE 802.11e

Extends the basic DCF to support service differentiation

  • Upcoming IEEE 802.11e MAC:
    • HCF: Hybrid Coordination Function has Controlled Channel Access Mechanism, it is used in infrastructure network
    • EDCF: Enhanced Distributed Coordination Function doesn’t need a central coordinator point, it is used in Ad-hoc network

July 1, 2003

edcf enhanced dcf
EDCF - Enhanced DCF

Class1

Class0

Class2

Class7

TC0

TC1

TC2

TC7

CW[TCi]

CW

DIFS

AIFS[TCi]

Internal Scheduler (Resolve Virtual Collisions)

Transmission attempt

EDCF

Transmission attempt

DCF

Many classes provide per flow differentiation

July 1, 2003

edcf limitations
EDCF Limitations

EDCF fails to provide QoS at high load

Bad Video Quality

Low Total Throughput

Audio

Video

Background

Throughput (in B/s)

Time (in sec)

July 1, 2003

our approach adaptive edcf 1
Our approach: Adaptive EDCF (1)

Goals :

  • improve the QoS for multimedia applications in all medium states
  • increase the total throughput in all medium states

Idea :

  • To protect Audio and Video transmissions, best effort queue increases its CW larger and reset a new backoff time, when it senses the channel is busy, during deferring periods
  • To decrease the wasted number of idle slots due to backoff in each contention cycle, a queue must decrease faster its backoff time after it senses the channel idle during a certain time
  • Each extension will help to realize the above goals

July 1, 2003

aedcf 2 1st extension
AEDCF(2): 1st extension

Our Solution :

  • First,extend the Fast Backoff mechanism, proposed for DCF in Florida U., to an adapted approach that differentiates between the different priority levels
  • 2 Backoff states :
  • Linear decrease (old)
  • Exponential decrease (new)

- Adapted to medium state

- Differentiate between traffic classes

Linear state

exponential state

Slot T.

Backoff_Time

Backoff_Threshold

0

Backoff_Counter decrease

July 1, 2003

aedcf 3 2nd extension
AEDCF (3): 2nd extension
  • Second, increase the contention window size and reset a new backoff time, when the channel is sensed busy, during deferring periods :

CW[pri] = min(CWmax[pri], 2 * CW[pri])

Priority

0 1 2 3

CWmax

1023 1023 31 15

  • Low priority flows will be punished
  • High priority flows will be protected

July 1, 2003

simulations topology and parameters 1
Simulations Topology and parameters (1)

Medium Bandwidth = 4.5 Mbytes/s

Audio

Audio

Video

Video

Node0

Node n

Node 1

Background

Background

Audio

Background

Video

Low load : n = 5, 1 Mbytes/s

Medium load : n = 11, 2.5 Mbytes/s

High load : n = 15, 3.5 Mbytes/s

Node2

July 1, 2003

slide15

Simulation Topologies and parameters (2)

MAC parameters for the three flows

July 1, 2003

aedcf flows throughput
AEDCF: Flows Throughput

Good multimedia flow performance in medium and high load cases

Also, Background flows have better throughput than in EDCF case

Throughput (in B/s)

Throughput (in B/s)

Time (in sec)

Time (in sec)

Throughput with AEDCF in 11 nodes topology

Throughput with AEDCF in 15 nodes topology

July 1, 2003

aedcf total throughput
AEDCF: Total Throughput

Our scheme also provides highest Total Throughput in high load case

Total Throughput (in B/s)

3.5 Mbytes/s Total sending rate

Total Throughput in 15 nodes topology

Time (in sec)

With our AEDCF scheme, the T.T is higher about 55 % more than with EDCF and 10 % more than DCF in this high load topology

July 1, 2003

slide18

Our approach: Adaptive DCF (1)

Extends DCF by our adapted fast backoff approach

Throughput with DCF

Throughput with FCR

Throughput (in B/s)

Throughput (in B/s)

Time (in sec)

Time (in sec)

ADCF provides best medium utilisation in this medium load case

Throughput (in B/s)

Throughput with ADCF

July 1, 2003

Time (in sec)

adcf 2 high load
ADCF (2): High load

Throughput with DCF

Throughput with FCR

Throughput (in B/s)

Throughput (in B/s)

Time (in sec)

Time (in sec)

Throughput with ADCF

We still need service differentiation to maintain a stable multimedia flows quality in high load

Throughput (in B/s)

Time (in sec)

July 1, 2003

adcf 3 total throughput
ADCF (3): Total Throughput

In medium and high load cases, ADCF provides the highest Total Throughput

2.75 Mbytes/s Total sending rate

Total Throughput (in B/s)

Total Throughput (in B/s)

3.5 Mbytes/s Total sending rate

Total Throughput in 11 nodes topology

Total Throughput in 15 nodes topology

Time (in sec)

Time (in sec)

In this medium load case, DCF is better than FCR

FCR is better than DCF only in high load case

July 1, 2003

conclusions and future work
Conclusions and Future Work
  • QoS support in IEEE 802.11 and 802.11e WLANs is not good enough
  • We propose an extension to the proposed 802.11e EDCF: Adaptive EDCF
    • Uses adaptive fast backoff mechanism
    • Provides more transmission opportunity to multimedia applications and higher total throughput during high load situations
  • we propose an extension to the standard 802.11 DCF: Adaptive DCF
    • Uses adaptive fast backoff mechanism
    • Provides better medium utilisation and higher total throughput in medium and high load cases
    • It is not good enough for multimedia applications in high load state
    • In this case, it is better to use AEDCF
  • Future work: Analytic modeling & Real Experimentation

July 1, 2003

slide22

Q & A

Thank you

Mohammad.Malli@sophia.inria.fr

July 1, 2003