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

Outline  e  Motivation  Goals  Proposed Scheme : DTMA  Functional Description of DTMA Entities  Handling Issues  Results

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

EDCF  EDCF – Enhanced Co-ordination Function  Part of HCF  Supports upto 8 traffic classes.  Uses Backoffs and AIFS for and AIFS forclassification.

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. CP CFP CAPCAP CAPCAP CPCP CPCP CPCP

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.

Goals  Theoretically Analyze e.  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.

DMTA : Dynamic Time Division Multiple Access  Adorns the PCF part of IEEE  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’.

DTMA Superframe Beacon New Beacon = Beacon + Cumm. Ack + Ordered Privileged List + Time for each slot Cumm. Ack DTMAEDCF All Nodes CompetePrivileged Nodes

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.

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

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

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

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.

Results  Average Delay Comparison  Throughput Comparison

Optimal Beacon Interval  Average Delay Comparison Comparison  Throughput Comparison Comparison

Thank You !!!!