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Determining Intra-Flow Contention along Multihop Paths in Wireless Networks

This paper explores the challenges and solutions for estimating bandwidth consumption in wireless networks where intra-flow contention occurs along multihop paths. Effective admission control is crucial for enabling Quality of Service (QoS) in these networks. We introduce two new methods for determining contention count without relying on high-power transmissions, allowing for more efficient bandwidth estimation. The proposed Pre-Reply Probe (PRP) and Route Request Tail (RRT) approaches leverage carrier-sensing information to enhance accuracy, reduce overhead, and improve network resources management.

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Determining Intra-Flow Contention along Multihop Paths in Wireless Networks

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  1. Determining Intra-Flow Contention along Multihop Paths in Wireless Networks K. Sanzgiri, I. Chakeres, E. Belding-Royer Department of Computer Science University of California, Santa Barbara Kimaya Sanzgiri

  2. Introduction • Admission control is essential for enabling QoS • To make admission control decision, network must • Determine available resources • Estimate resource consumption of new flow • We focus on estimation of bandwidth consumption of a flow Kimaya Sanzgiri

  3. Challenges in Estimating Bandwidth Consumption • Wireless transmissions consume bandwidth at all nodes within carrier-sensing range (assuming CSMA-based medium access) Carrier-sensing range of node Y Z Nodes W, X and Z cannot transmit when node Y is transmitting Y W X Kimaya Sanzgiri

  4. Challenges in Estimating Bandwidth Consumption • Nodes along a multihop path may lie within each other’s carrier-sensing range • This leads to intra-flow contention Carrier-sensing range of node Y Z Packets of flow F contend for medium access at nodes W, X and Y Y W X Flow F Kimaya Sanzgiri

  5. Intra-Flow Contention • Due to intra-flow contention, bandwidth consumption of a flow at a node becomes a multiple of that requested by the application Carrier-sensing range of node Y Z Bandwidth consumed by flow F at nodes W, X, Y each is 3 times the single-hop bandwidth Y W X Flow F Kimaya Sanzgiri

  6. Contention Count • Contention Count (CC) at a node = Intersection of (set of carrier-sensing neighbors) with (set of nodes on multihop path) + 1 • Bandwidth consumption of flow = CC x (single-hop bandwidth consumption) • To estimate bandwidth consumption, CC must be calculated Kimaya Sanzgiri

  7. Examples of Contention Count Contention Count at X = 5 Contention Count at Y = 7 V A U B P T C Q X Y R D S E F Carrier-sensing range of node X Carrier-sensing range of node Y Kimaya Sanzgiri

  8. Challenges in Determining Contention Count • Node cannot directly communicate with all carrier-sensing neighbors (CSN) • Previously used approaches: • High power transmissions • Reduced spatial reuse, higher energy consumption • Multihop transmissions • Inaccurate, higher overhead Kimaya Sanzgiri

  9. Related Work • Intra-flow contention ignored by most • CACP [Yang et al. 2003] • First to correctly consider intra-flow contention • High-power broadcast to communicate with CSN at each hop during reply phase of route discovery Kimaya Sanzgiri

  10. Our Contribution • Two new approaches to determine contention count • No high-powered transmissions • Key Idea: Use carrier-sensing information from regular-powered transmissions to derive information about CSN Kimaya Sanzgiri

  11. Carrier-Sensing Information • Graph of received signal strength vs. time • Duration of transmissions from CSN can be sensed RSS X RxThresh Y CSThresh time tx ty Kimaya Sanzgiri

  12. Effect of Collisions Colliding packets X and Y are sensed as a single packet of duration tz • Collisions affect packet duration measurements if neither signal is sufficiently stronger than the other RSS RxThresh X Y CSThresh time tz Kimaya Sanzgiri

  13. Proposed Approaches • Two approaches proposed: • Pre-Reply Probe (PRP) • Route Request Tail (RRT) • Integrated with route discovery of reactive routing protocol (AODV) • Nodes record duration of all sensed transmissions • Duration used to infer packet length (assuming common data rate) Kimaya Sanzgiri

  14. Pre-Reply Probe (PRP) • Prior to RREP, destination sends Pre-Reply Probe Message (PRPM) • Size of PRPM randomly selected by destination • Identifies unique transmission duration • PRPM forwarded to source along route • Transmission duration at each hop recorded by CSN of that hop • Source locally broadcasts PRPM Kimaya Sanzgiri

  15. PRP Example PRPM of length L PRPM of length L PRPM of length L PRPM of length L P Q R S Recorded pkt lengths: L L L L L L L L L L Kimaya Sanzgiri

  16. PRP Example (cont.) P Q R S Recorded pkt lengths: L L L L L L L L L L Kimaya Sanzgiri

  17. PRP (cont.) • Next, destination sends RREP • RREP contains size of corresponding PRPM (L) • Intermediate nodes calculate CC when processing RREP • CC = (Number of transmissions sensed of duration L) + 1 Kimaya Sanzgiri

  18. PRP Example (cont.) RREP P Q R S L L Recorded pkt lengths: L L L L L L L L Contention count: 3 4 4 3 Kimaya Sanzgiri

  19. PRP Analysis • Alleviates many of the drawbacks of CACP • Main advantage is no high power transmissions • Drawbacks: • Additional control message • Delay before RREP • Possible errors in case of collisions or retransmissions Kimaya Sanzgiri

  20. Route Request Tail (RRT) • Removes some drawbacks of PRP • Random-sized tail attached to RREQ • At each hop • Unique tail size generated • Results in unique RREQ size • Tail of previous hop replaced • RREQ sizes accumulated in RREQ packet Kimaya Sanzgiri

  21. RREQ packet in RRT Regular RREQ contents RREQ size at hop 0 RREQ size at hop 1 ….. RREQ size at last hop Tail attached by last hop Kimaya Sanzgiri

  22. RRT (cont.) • Nodes record sensed packet durations as in PRP • Destination includes list of RREQ sizes in RREP • Intermediate nodes check which packet sizes listed in the RREP were sensed • CC = (Number of sizes sensed) + 1 Kimaya Sanzgiri

  23. RRT Analysis • Retains benefits of PRP • Removes extra control message and delay • Increases RREQ size • Greater byte overhead • Higher probability of collisions and errors in duration measurement Kimaya Sanzgiri

  24. Performance Analysis • Comparison with CACP • Analytical comparison • Simulation-based (NS-2) evaluation • 50 nodes in a 1500m x 650m area • CBR traffic • Number of sessions varied to evaluate performance under different load conditions • No mobility Kimaya Sanzgiri

  25. CC Error Kimaya Sanzgiri

  26. CC Latency Kimaya Sanzgiri

  27. Control Packets Sent Kimaya Sanzgiri

  28. Control Packets Received Kimaya Sanzgiri

  29. Conclusion • Carrier-sensing information, such as duration of sensed transmissions, can be used to infer information about CSN • PRP and RRT determine intra-flow contention with low error • Error outweighed by benefits • Lower energy consumption • Reduced network load • Faster response time Kimaya Sanzgiri

  30. Thank You Questions/Comments? Kimaya Sanzgiri

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