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 !
– 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
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
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
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 !
– 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
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
[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