1. November 4, 2003APOC 2003 Wuhan, China 1/14 Demand Based Bandwidth Assignment MAC Protocol for Wireless LANs Presented by Ruibiao Qiu Department 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

2. November 4, 2003APOC 2003 Wuhan, China 2/14 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.

3. November 4, 2003APOC 2003 Wuhan, China 3/14 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.

4. November 4, 2003APOC 2003 Wuhan, China 4/14 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

5. November 4, 2003APOC 2003 Wuhan, China 5/14 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.

6. November 4, 2003APOC 2003 Wuhan, China 6/14 MAC LAYER

7. November 4, 2003APOC 2003 Wuhan, China 7/14 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.

8. November 4, 2003APOC 2003 Wuhan, China 8/14 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

9. November 4, 2003APOC 2003 Wuhan, China 9/14 DBBA NETWORK SIMULATION MODEL

10. November 4, 2003APOC 2003 Wuhan, China 10/14 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.

11. November 4, 2003APOC 2003 Wuhan, China 11/14 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.

12. November 4, 2003APOC 2003 Wuhan, China 12/14 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.

13. November 4, 2003APOC 2003 Wuhan, China 13/14 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.

14. November 4, 2003APOC 2003 Wuhan, China 14/14 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.