Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Fast Resilient Jumbo Frames in Wireless LANs

Fast Resilient Jumbo Frames in Wireless LANs

Anand Iyer

July 15, 2009
Tweet

More Decks by Anand Iyer

Other Decks in Research

Transcript

  1. Fast Resilient Jumbo
    Frames in Wireless LANs
    Apurv Bhartia
    University of Texas at Austin
    [email protected]
    Joint work with
    Anand Padmanabha Iyer, Gaurav Deshpande, Eric
    Rozner and Lili Qiu
    IWQoS 2009
    July 15, 2009

    View Slide

  2. 2
    Motivation
    •  Lossy wireless medium
    •  Novel techniques have been proposed …
    … but each of them alone is insufficient
    Partial Recovery
    Jumbo Frames Rate Adaptation
    Our goal: identify the synergy between these
    techniques and exploit it

    View Slide

  3. 3
    State of the Art
    •  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
    •  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
    Holistic Approach is missing !

    View Slide

  4. 4
    Our Contributions
    •  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

    View Slide

  5. 5
    Synergy Between Design Space
    Partial Recovery
    Jumbo Frames Rate Adaptation
    Constant MAC overhead
    Reduces relative cost of
    RTS/CTS
    Loss Increases with
    frame size
    Increases effectiveness of jumbo
    frames
    Less collisions – effective recovery
    Higher tx rates!
    Increased tx rates
    reduces contention losses
    Reduces effective data loss
    rate
    Better partial recovery
    Higher tx rates – increases
    relative MAC overhead
    More data for constant
    overhead
    Benefit increases with
    increased tx rates
    Partial Recovery Aware Rate Adaptation
    Partial Recovery Aware Rate Adaptation
    Partial Recovery Aware Rate Adaptation

    View Slide

  6. 6
    Resilient Jumbo Frames
    S R
    •  Use jumbo frames
    –  High throughput in good conditions
    –  In bad conditions …
    •  … re-transmit only corrupted segments
    –  Saves the overhead of retransmitting complete frames
    2.5 ACK

    View Slide

  7. 7
    Resilient Jumbo Frame
    •  Data Frames
    •  Core Components
    –  Resilient Jumbo Frames which applies partial
    recovery to jumbo frames
    –  Partial recovery ‘aware’ rate adaptation
    Header
    4 4 4
    4 4
    4
    1 1 2 2
    Segment 1 CRC Segment 2 CRC Segment N CRC
    Frame ID Type Rate Bitmap SS
    Header
    CRC
    Length

    View Slide

  8. 8
    Resilient Jumbo Frame (Cont.)
    •  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
    CRC
    Header
    Frame
    Offset N
    Segment
    Bitmap N
    Start Frame
    Seg No
    Type Rate
    Frame
    Bitmap

    View Slide

  9. 9
    Approach
    •  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

    View Slide

  10. 10
    Partial Recovery Aware Rate Adaptation
    –  Traditional schemes identify optimal rate using
    frame loss rate
    •  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 !

    View Slide

  11. 11
    Partial Recovery Aware Rate Adaptation
    •  Estimating Channel Condition
    –  Sender periodically broadcasts probe packets
    –  Sent at different data rates
    •  CurrRate
    r
    [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
    Type Payload
    Probe ID Rate
    Header
    CRC
    Per rate

    View Slide

  12. 12
    Partial Recovery Aware Rate Adaptation
    •  Probe Response
    –  Sent by the receiver
    –  Estimates the channel condition using
    •  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
    Type
    Probe Response ID Rate1
    Frame
    CRC
    BER1 HL1 Rate1 BER1 HL1

    View Slide

  13. 13
    Partial Recovery Aware Rate Adaptation
    •  Sender selects the rate that gives the best
    throughput estimation
    T = ∑ Pi
    × (Backoff + DIFS +
    i=1..MaxRetries + 1
    DATA + SIFS + ACK + useRTS + RTSOverhead )
    preambleTime +
    (HS + NSi
    + segmentSize)
    rate
    Pi
    =
    1 i = 1
    Pi-1
    × (HL + (1 – HL) × (1- (1 – SL) )) otherwise
    NSi-1
    Throughput = (NS1
    – NSMaxRetries + 2
    ) × SegmentSize/T
    NSi
    =
    30 i = 1
    NSi-1
    × (HL + (1 – HL) × SL ) otherwise
    RTS + SIFS + CTS + SIFS
    NSi
    Probability of sending the ith tx
    Time for ith data tx
    No of segments in ith tx

    View Slide

  14. 14
    Testbed Topology
    •  24 machines
    •  Madwifi driver and
    CLICK toolkit
    •  Initial rate =
    24Mbps
    •  Tx Power = 18 dBm
    Total throughput
    Per flow throughput
    Jain’s Fairness Index

    View Slide

  15. 15
    Schemes Compared
    •  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

    View Slide

  16. 16
    Experimental Results: Single Flow
    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

    View Slide

  17. 17
    Experimental Results: Multiple Flows
    0
    5
    10
    15
    20
    25
    -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
    Randomly chosen flows!
    FRJ constantly outperforms
    More collisions => increase
    in header losses
    FRJ benefit ranges from 10% (1 flow) to
    64% (6 flows)

    View Slide

  18. 18
    Experimental Results : Multiple Flows
    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

    View Slide

  19. 19
    Experimental Results: Multiple Flows
    •  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!

    View Slide

  20. 20
    Conclusion
    •  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

    View Slide

  21. Thank you!
    [email protected]

    View Slide

  22. 22
    0
    5
    10
    15
    20
    25
    -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

    View Slide