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TCP Performance Optimizations forWireless Sensor Networks
 

TCP Performance Optimizations for Wireless Sensor Networks

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EWSN 2012, Trento

EWSN 2012, Trento

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    TCP Performance Optimizations forWireless Sensor Networks TCP Performance Optimizations for Wireless Sensor Networks Presentation Transcript

    • EWSN 2012TCP Performance Optimizations forWireless Sensor NetworksPhilipp Hurni, Ulrich Bürgi, Markus Anwander,Torsten BraunResearch Group ―Communication and Distributed Systems‖Institute of Computer Science and Applied MathematicsUniversity of Bern, Switzerlandbraun@iam.unibe.ch, cds.unibe.ch
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Overview > Motivation and Related Work — Reasons for Poor TCP Performance in Wireless Multi-Hop Networks — Optimization of TCP in WSNs > Proposed Optimization Concepts — Caching and Congestion Control (cctrl) Module including Channel Activity Monitoring — Spatial Reuse by Multiple TCP Connections > Results by Testbed Experiments — Throughput — Radio On-Time as Energy Consumption Measure > Conclusions Trento, February 15, 2012 2
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Reasons for Poor TCP Performance in Wireless Multi-Hop Networks > Higher bit error rates and packet loss > Underlying MAC protocols (exponential back-off, hidden / exposed nodes) > TCP end-to-end error and congestion control mechanisms TCP data segment loss TCP acknowledgement loss Trento, February 15, 2012 3
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Optimization of TCP in WSNs > Distributed TCP Caching (Dunkels et al., 2004) > TCP Support for Sensor Networks (Braun et al., 2007) Trento, February 15, 2012 4
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Caching and Congestion Control (cctrl) Module > is aware of all TCP packets forwarded by a node by interception of outbound packets. > allocates buffer for 2 packets per TCP connection (1 for each direction, µIP has max. 1 unacknowledged TCP data segment per connection) Trento, February 15, 2012 5
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks cctrl Functions > Caching of — complete TCP data segments and scheduling of retransmission timer (RTO = 3 ∙ RTTestimated, RTTestimated = estimated RTT between intermediate node and destination) — TCP/IP header for TCP acknowledgements > Local retransmission of TCP data segment (max. 3 attempts), when RTO expires prior to TCP acknowledgement reception (a) > Removal of TCP data segments, if acknowledgement number of TCP acknowledgement > sequence number of cached TCP data segment > For retransmitted TCP data segments, for which a TCP acknowledgement has been received: discard TCP data segment; regenerate TCP acknowledgement (b) Trento, February 15, 2012 6
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Channel Activity Monitoring > MAC proxy notifies cctrl upon reception of any packet and stores a timestamp in activity history. > cctrl continuously calculates channel activity level (= # overheard packets by MAC proxy during the last time period RTTestimated) > Observation: — Channel activity level of most nodes = 0 during long idle periods — Long idle periods by – TCP data segment loss at one of the first hops – TCP acknowledgement loss close to its destination (i.e. TCP data segment’s source). > Approach: — Split RTO into: – RTO1 = 3 ∙ RTTestimated ∙ 2/3 – RTO2 = 3 ∙ RTTestimated ∙ 1/3 — When RTO1 expires: early retransmission, if channel activity level = 0; otherwise: retransmission when RTO2 expires. — Triggers early local retransmissions close to destination Trento, February 15, 2012 7
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks MAC Proxy Trento, February 15, 2012 8
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Channel Activity Levels with X-MAC Trento, February 15, 2012 9
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Long Idle Periods Trento, February 15, 2012 10
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Spatial Reuse by Multiple TCP Connections Trento, February 15, 2012 11
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Testbed Experiments > 7 TelosB nodes in different rooms of a 3 floor building using U Bern’s Wisebed testbed > Receiver node 1 > Sender nodes 2-7 > Experiments with different MAC protocols for 10 minutes, 15 repetitions > 16 bytes payload > 79 bytes per TCP data segment > 63 bytes per TCP acknowledgement > Total: approx. 2500 experiments during > 400 hours Trento, February 15, 2012 12
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Throughput Trento, February 15, 2012 13
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Radio On-Time as Energy Consumption Measure Trento, February 15, 2012 14
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Throughput with Multiple Connections Trento, February 15, 2012 15
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Overall Comparison of Throughput Trento, February 15, 2012 16
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Overall Comparison of Energy Consumption Trento, February 15, 2012 17
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Cross-Traffic Measurements Trento, February 15, 2012 18
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Cross-Traffic Throughput Trento, February 15, 2012 19
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Cross-Traffic Comparison Trento, February 15, 2012 20
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Conclusions > Implementation of caching, local TCP data segment retransmission, and TCP acknowledgement regeneration in intermediate nodes on top of several WSN MAC protocols > NullMAC and LPP provide good response to local retransmission. Results with ContikiMAC are worse. > cctrl can improve performance and energy efficiency. > Spatial reuse by multiple TCP connections can further improve performance. > Best performance and energy efficiency with cctrl and NullMAC ! → adaptive MAC protocols (Hurni et al., 2010) Trento, February 15, 2012 21
    • Torsten Braun:TCP Performance Optimizations for Wireless Sensor Networks Thanks for your attention ! > braun@iam.unibe.ch > http://cds.unibe.ch Trento, February 15, 2012 22