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QoS Guarantees for Real Time Applications in 802.11 WLANs

QoS Guarantees for Real Time Applications in 802.11 WLANs. Kiran P Diwakar Guide: Prof. Sridhar Iyer. Outline. 802.11e Motivation Goals Proposed Scheme : DTMA Functional Description of DTMA Entities Handling Issues Results. IEEE 802.11 e. Proposed Variant to provide QoS in 802.11.

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QoS Guarantees for Real Time Applications in 802.11 WLANs

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  1. QoS Guarantees for Real Time Applications in 802.11 WLANs Kiran P Diwakar Guide: Prof. Sridhar Iyer

  2. Outline • 802.11e • Motivation • Goals • Proposed Scheme : DTMA • Functional Description of DTMA Entities • Handling Issues • Results

  3. IEEE 802.11 e • Proposed Variant to provide QoS in 802.11. • Overcomes the ‘flat’ nature of legacy 802.11. • Introduces new differentiating parameters • AIFS, variable CW. • Two methods of Channel Access • EDCF • HCF

  4. EDCF • EDCF – Enhanced Co-ordination Function • Part of HCF • Supports upto 8 traffic classes. • Uses Backoffs and AIFS for classification.

  5. HCF • HCF – Hybrid Co-ordination Function • Hybrid Co-ordinator, collocated at AP. • Allocates TXOPs to WSTAs. • TXOP allocated during both CP and CFP • Several CAPs defined in one CP. CFP CP CAP CAP CP CP CP

  6. Motivation • Most works propose enhancements to DCF. • PCF not fully optimized. • Poll / Acks huge overhead when the number of stations is high. • Transmission Times : • Data (512 bytes) : 90 microsec • Poll / Acknowledgement : 40 microsec • Doing away with the individual polls / acks => more time for data transmission => more throughput and less delay => better QoS.

  7. Goals • Theoretically Analyze 802.11e. • Have a more intelligent Access Point. • Add more determinism. • AP has all the required info from node and hence can schedule better and QoS. • Reduce the average delay. • Optimize the overall throughput of the network. • Prove that the proposed scheme has stricter and lesser delays than existing ones.

  8. DMTA : Dynamic Time Division Multiple Access • Adorns the PCF part of IEEE 802.11 • Dynamically allots transmission slots. • Explicit control information annulled. • No Polls / Acknowledgements required. • Privileged nodes get explicit channel access in PCF. • In DCF, privileged nodes compete with lesser backoffs and AIFS. • Gives lesser delays for nodes associated as ‘high priority’.

  9. DTMA Superframe DTMA EDCF New Beacon = Beacon + Cumm. Ack + Ordered Privileged List + Time for each slot Privileged Nodes All NodesCompete Beacon Cumm. Ack

  10. Functional Description of Access Point • On reception of the Association / Dissociation request, manipulate the privileged / non-privileged list based on the bit set. • On the receipt of Data from node, add the node id to the cummulative ack-list. • At the end of slotted-CFP, send the cummulative ack-list. • Calculate the slot-size.

  11. Functional Description of Access Point • On receipt of request_to_join from an out of list node, reset the the not_to_schedule_flag, so from the next round, node will get slot. • If the AP and node both have data for each other, the AP schedules the node such that they transmit in alternate rounds. • On receipt of ‘Null frame’, pin node as mark_dont_schedule

  12. Access Point Cumm. Ack DCF ON DATA DATA DATA ACK C_Ack 1, 2, # C_Ack 1, 2, # C_Ack 1, 2, # C_Ack 1, 2, # C_Ack 1, 2, # BO=7 BO=3 BO=4 BO=2 BO=5 BO=2 BO=5 BO=4 BO=9 BO=7 BO=9 BO=2 ACK ACK DATA DATA DATA Beacon Beacon Beacon Beacon Beacon 1-2-3 1-2-3 1-2-3 1-2-3 1-2-3 P P P STA STA STA STA STA Id=4 Id=1 Id=2 Id=3 Id=5 1 ,2 ,# Beacon

  13. Access Point Cumm. Ack DATA DATA DATA ACK C_Ack 1, 2, # C_Ack 1, 2, # C_Ack 1, 2, # C_Ack 1, 2, # C_Ack 1, 2, # BO=5 BO=4 BO=5 BO=7 BO=2 BO=4 BO=3 BO=9 BO=2 BO=7 BO=9 BO=2 ACK ACK DATA DATA DATA Beacon Beacon Beacon Beacon Beacon 1-2-3 1-2-3 1-2-3 1-2-3 1-2-3 P P P STA STA STA STA STA Id=4 Id=1 Id=2 Id=3 Id=5 1 ,2 ,# Beacon

  14. Handling Issues • Beacon gets garbled. • Ack_list gets garbled. • Node with multiple real-time flows. • Node off the list wants to get back on the list. • Synchronization issue.

  15. Results • Throughput Comparison • Average Delay Comparison

  16. Optimal Beacon Interval • Average Delay Comparison • Throughput Comparison

  17. Thank You !!!!

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