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Demand Based Bandwidth Assignment MAC Protocol for

Wireless LANs

Presented by Ruibiao QiuDepartment of Computer Science and Engineering,

Washington University

St. Louis, MO 63130, USA

K. Murugan, B. Dushyanth, E. Gunasekaran, S. Arivuthokai, R. S. Bhuvaneswaran, S. Shanmugavel

Department of Computer Science, CEG, College of Engineering

Anna University, Chennai, India

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INTRODUCTION• IEEE 802.11

– Up to 54Mbps of raw physical data. – Uses Aloha protocol to share the wireless medium. – Drawback:

• cannot work under high traffic load.

• Wireless medium is highly bandwidth and power limited– A TDMA solution may increase channel bandwidth

utilization– TDMA major disadvantage

• Fixed time slots could limit the number of nodes.

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INTRODUCTION

• DAMA-TDMA – Used by many satellite networks where the

time slots are allocated dynamically.

• We propose a variation of DAMA-TDMA– Demand Based Bandwidth Assignment

(DBBA) – Challenge

• Avoid collision during the demand request contention period.

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IEEE 802.11 MAC PROTOCOL

• CSMA/CA scheme.

• MAC layer depends on acknowledgement packet to determine collision. – Receiver

• Sends an acknowledge before stipulated time interval after completion of the transmission.

– Transmitter• If no acknowledgement within the timeout period,

assumes that the packet loss and retransmits

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IEEE 802.11 MAC PROTOCOL

• Low bandwidth utilization due to MAC layer constraints.

• Number of nodes increases– Collision probability increases– Overall network bandwidth lower

• The latency depends on traffic conditions with no bandwidth guarantee.

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MAC LAYER

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DBBA-MAC PROTOCOL

• Two components in a network– A primary controller node – Multiple station nodes

• DBBA frame has n+3 time slots– Beacon time slot – Demand request time slot– Demand Assignment time slot– Data Time slots.

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DBBA-MAC PROTOCOL• Controller

– Broadcasts a beacon packet during the Beacon time slot at the beginning of each frame.

– The beacon frame contains• network SSID, frame information, timeslot information.

• Station node– Sends a demand request packet to the controller during the Demand

Request time slot– Contains

• Source node ID, destination node ID, date size, and QoS requirement.• Controller

– Processes all the requests– Generates the bandwidth assignment table.– Broadcasts acknowledgement to all accepted requests in the Demand

Assignment time slot

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DBBA NETWORK SIMULATION MODEL

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SIMULATION• Simulation Model:

– Three classes: scheduler, modem, packet generator• Scheduler

– Collects the desired transmission time from all stations– Determines the modem with the lowest desired transmission time stamp– Detects and notifies collision

• Modem– Depicts the behavior of stations with information from the packet

generator.– Returns the packet details to scheduler.– Waits for acknowledge of the transmitted packet from the scheduler

• Packet Generator– Depicts a user generating traffic data. – One instance per Modem. – The uniformly random distributed packet length with three packets types.

• Small, medium, large.

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No of Nodes vs Throughput (Traffic Load = 0.8)

0102030405060708090

100

3 6 9 12 15 18 21 24 27 30No of Nodes

Thro

ughp

ut (%

)

DDBA

IEEE802_11

No of Nodes vs Collisions (Traffic Load = 0.8)

0102030405060708090

100

3 6 9 12 15 18 21 24 27 30No of Nodes

Collis

ions

DBBA

IEEE802_11

SIMULATION RESULT

• As the number of nodes increases, the throughput of DBBA slightly increases due to higher traffic loads.

• The number of collisions is 5 % to 8% lesser than 802.11 as the number of nodes increases.

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Traffic Load vs Throughput (No of Nodes = 100)

0102030405060708090

100

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Traffic Load

Thro

ughp

ut (%

)

DBBA

IEEE802_11

Traffic Load vs Collisions (No of Nodes = 20)

0102030405060708090

100

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Traff ic Load

Collis

ions

(%)

DBBA

IEEE802_11

SIMULATION RESULT

• Throughput and collisions of both 802.11 and DBBA are compared with different traffic loads.

• Throughput of DBBA increases as traffic load increases

• Amount of collisions is 5% to 8% lesse than 802.11 as the traffic load increases.

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No of Nodes vs Average Latency (Traffic Load = 0.8)

0800

160024003200400048005600640072008000

3 6 9 12 15 18 21 24 27 30

No of Nodes

Avg

. Lat

ency

(US)

DBBA

IEEE802_11

Traffic Load vs Average Latency (No of Nodes = 20)

0500

100015002000250030003500400045005000

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Traffic Load

Avg

. Lat

ency

(US)

DBBA

IEEE802_11

SIMULATION RESULT

• Average latency of DBBA and 802.11 is compared with increasing number of nodes and different traffic loads.

• Delay is little more than the 802.11 as the number of nodes increases with traffic load 0.8

• Under different traffic load conditions, the average latency of DBBA protocols is higher.

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CONCLUSION

• Demand Based Bandwidth Assignment (DBBA) protocol is proposed.– Higher bandwidth utilization– Larger number of stations in one cell– Less propagation delay– More power efficiency– Provide better quality of service.

• Efficiency increased without affecting the overall throughput

• Future work– Allocation of dedicated slots for a complete session to

reduce the delay for the constant bit rate services.