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Fast Resilient Jumbo Frames in Wireless LANs
- 1. FFaasstt RReessiilliieenntt JJuummbboo FFrraammeess iinn WWiirreelleessss LLAANNss AAppuurrvv BBhhaarrttiiaa UUnniivveerrssiittyy ooff TTeexxaass aatt AAuussttiinn aappuurrvvbb@@ccss..uutteexxaass..eedduu JJooiinntt wwoorrkk wwiitthh AAnnaanndd PPaaddmmaannaabbhhaa IIyyeerr,, GGaauurraavv DDeesshhppaannddee,, EErriicc RRoozznneerr aanndd LLiillii QQiiuu IIWWQQooSS 22000099 JJuullyy 1155,, 22000099
- 2. Jumbo Frames Rate Adaptation Our goal: identify the synergy between these techniques and exploit it 2 MMoottiivvaattiioonn • Lossy wireless medium • Novel techniques have been proposed … Partial Recovery … but each of them alone is insufficient
- 3. 3 SSttaattee ooff tthhee AArrtt • Jumbo Frames – Proprietary solutions for frame aggregations [Atheros Super G, TI frame concatenation] – 802.11n frame aggregation standard • Require specific hardware support • Entire packet needs to be retransmitted Holistic Approach is missing ! • Partial Packet Recovery – Require specific hardware support [MRD, SOFT, PPR] – Leverage PHY layer information [SOFT, PPR] • if PHY layer information is available, FRJ can benefit to provide higher gain • Rate Adaptation – SampleRate, ONOE (madwifi), RRAA – Over-estimates the actual loss rate • Adapt rate according to frame loss rate • Over-estimates the actual loss rate
- 4. 4 OOuurr CCoonnttrriibbuuttiioonnss • Identify interactions between the three techniques – Exploit the synergy between the schemes – Works for both single and multi-hop topologies • Develop resilient jumbo frames – Achieve high throughput under both low and high loss conditions • Develop partial recovery aware rate adaptation • Develop a prototype implementation
- 5. SSyynneerrggyy BBeettwweeeenn DDeessiiggnn SSppaaccee Reduces effective data loss rate Better partial recovery PPPPPPaaaaaarrrrrrttttttiiiiiiaaaaaallllll RRRRRReeeeeeccccccoooooovvvvvveeeeeerrrrrryyyyyy AAAAAAwwwwwwaaaaaarrrrrreeeeee RRRRRRaaaaaatttttteeeeee AAAAAAddddddaaaaaappppppttttttaaaaaattttttiiiiiioooooonnnnnn 5 Increases effectiveness of jumbo frames Less collisions – effective recovery Partial Recovery Loss Increases with frame size Jumbo Frames Rate Adaptation Constant MAC overhead Reduces relative cost of RTS/CTS Higher tx rates! Increased tx rates reduces contention losses Higher tx rates – increases relative MAC overhead More data for constant overhead Benefit increases with increased tx rates
- 6. RReessiilliieenntt JJuummbboo FFrraammeess S R 6 • Use jumbo frames 2.5 ACK – High throughput in good conditions – In bad conditions … • … re-transmit only corrupted segments – Saves the overhead of retransmitting complete frames
- 7. RReessiilliieenntt JJuummbboo FFrraammee • Core Components – Resilient Jumbo Frames which applies partial recovery to jumbo frames – Partial recovery ‘aware’ rate adaptation Segment 1 CRC Segment 2 CRC Segment N CRC 7 • Data Frames Header 4 4 4 Frame ID Type Rate Bitmap SS Header Length CRC 4 1 1 4 2 2 4
- 8. Resilient JJuummbboo FFrraammee ((CCoonntt..)) Header CRC Frame 8 • Receiver Feedback – Combination of MAC-layer and 2.5-layer ACKs – MAC-layer ACKs • Adjustment of back-off window in IEEE 802.11 • Increased reliability and efficiency than 2.5 ACKs – 2.5-layer ACKs • To support partial recovery • Unicast for improved reliability and cumulative Frame Offset Segment Bitmap 1 Frame Offset N Segment Bitmap N Start Frame Seg No Type Rate Frame Bitmap
- 9. 9 AApppprrooaacchh • Retransmission – Disable MAC layer retransmissions • set MAC retry count = 0 • Retransmit the frames at the 2.5-layer – Triggered by • 2.5-layer ACKs – If 1st Retx: frames with higher seq nos or some segments in this frame are ACKed [first data transmissions is in-order] – If 2nd or higher: some new segments in this frame are ACKed • Retransmission Timeout – Standard approach as in TCP
- 10. Partial RReeccoovveerryy AAwwaarree RRaattee AAddaappttaattiioonn – Traditional schemes identify optimal rate using frame loss rate 10 • Overestimates the loss rate • Lower data transmissions rates are selected – Challenges for the ‘new’ scheme • Accurate estimation of channel condition at various data rates • Selecting rate that maximizes throughput under partial recovery Estimate throughput based on loss statistics !
- 11. Partial RReeccoovveerryy AAwwaarree RRaattee AAddaappttaattiioonn • Estimating Channel Condition – Sender periodically broadcasts probe packets – Sent at different data rates 11 • CurrRater [current data rate] • CurrRate-r [one rate below the current data rate] • CurrRate+ r [one rate above the current data rate] – Sent at a frequency of 5 probes/second • Limit the overhead Probe ID Type Rate Header Payload CRC Per rate
- 12. Partial RReeccoovveerryy AAwwaarree RRaattee AAddaappttaattiioonn • Probe Response – Sent by the receiver – Estimates the channel condition using 12 • Header Loss Rate (HL) – header corruption • Segment Loss Rate (SL) – segment corruption • Communicates this info using probe response – Transmitted via MAC-layer unicast • High reliability – Default Probe response [HL = 1, SL = 1] • To account for lost probes Probe Response ID Type Rate1 Frame BER1 HL1 Rate1 BER1 HL1 CRC
- 13. Partial RReeccoovveerryy AAwwaarree RRaattee AAddaappttaattiioonn • Sender selects the rate that gives the best throughput estimation RTS + SIFS + CTS + SIFS T = Σ P× (Backoff + DIFS + i NSi No of segments in ith tx 30 i = 1 NSi-1 × (HL + (1 – HL) × SL ) otherwise 13 i=1..MaxRetries + 1 DATA+ SIFS + ACK + useRTS + RTSOverhead ) (HS + + segmentSize) preambleTime + rate Time for ith data tx Probability of sending the ith tx Pi = NSi = 1 i = 1 P× (HL + (1 – HL) × (1- (1 – SL) NSi-1 )) i-1 otherwise Throughput = (NS1 – NSMaxRetries + 2) × SegmentSize/T
- 14. 14 TTeessttbbeedd TTooppoollooggyy • 24 machines • Madwifi driver and CLICK toolkit • Initial rate = 24Mbps • Tx Power = 18 dBm Total throughput Per flow throughput Jain’s Fairness Index
- 15. 15 SScchheemmeess CCoommppaarreedd • Sample Rate using 1500 byte frames [SR/1500-bytes] • Sample Rate using 3000 byte frames [SR/3000-bytes] – Same as SR/1500, but uses jumbo frames – Similar to Atheros Super G Fast Frame feature • FRJ using 3000 byte frames, 30 segments With and without RTS/CTS
- 16. Experimental RReessuullttss:: SSiinnggllee FFllooww 16 Throughput (Mbps) Cumulative Fraction SR/1500: 0.68 Mbps SR/3000: 0.68 Mbps FRJ: 1.1 Mbps SR/1500: 14.17 Mbps SR/3000: 16.93 Mbps FRJ: 23.81 Mbps Moderate Link Conditions: Partial Recovery is more effective FRJ benefit is 40.6% - 68.0% under single flow
- 17. Experimental Results: MMuullttiippllee FFlloowwss More collisions => increase in header losses 17 25 Randomly chosen flows! 20 15 10 5 0 -5 1 2 4 6 8 # Flows Average Total Throughput (Mbps) FRJ SR/1500 bytes SR/3000 bytes FRJ w/ RTS SR/1500 bytes w/ RTS SR/3000 bytes w/ RTS Schemes w/o RTS/CTS perform well FRJ constantly outperforms FRJ benefit ranges from 10% (1 flow) to 64% (6 flows)
- 18. Experimental RReessuullttss :: MMuullttiippllee FFlloowwss 18 Throughput (Mbps) Cumulative Fraction Average Throughput SR/1500: 0.84 Mbps FRJ: 1.68Mbps SR/3000: 1.05 Mbps SR/1500: 0.30 Mbps SR/3000: 0.38 Mbps FRJ: 0.57 Mbps
- 19. Experimental Results: MMuullttiippllee FFlloowwss 19 • Fairness – Difference is within 10% – Most cases it is close to 0 # Flows Fairness Index FRJ’s performance gain does not come at the cost of compromising fairness!
- 20. 20 CCoonncclluussiioonn • Main contributions – Identify interplay between jumbo frames, PPR and rate adaptation • Jumbo frames with partial recovery • Partial recovery aware rate adaptation – Demonstrate the effectiveness of this solution through testbed experiments • Future work – More effective partial recovery schemes and coding techniques – Dynamically configurable RTS/CTS – FRJ-aware route selection
- 22. 22 25 20 15 10 5 0 -5 1 2 4 6 8 # Flows Average Total Throughput (Mbps) FRJ SR/1500 bytes SR/3000 bytes FRJ w/ RTS SR/1500 bytes w/ RTS SR/3000 bytes w/ RTS
Editor's Notes
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