1 / 17

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.

zocha
Télécharger la présentation

QoS Guarantees for Real Time Applications in 802.11 WLANs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 !!!!

More Related