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TCP over Bluetooth: Simulation and Performance

TCP over Bluetooth: Simulation and Performance. Members: Raymond Liu raymondl@ucla.edu Tutor: Yeng-Zhong Lee yenglee@cs.ucla.edu. Outline. Introduction Motivation Goal Simulation Design. Introduction. Bluetooth vs 802.11 Similarities Radio frequency at ≈ 2.4 - 2.5 GHz Differences

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TCP over Bluetooth: Simulation and Performance

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  1. TCP over Bluetooth: Simulation and Performance Members: Raymond Liu raymondl@ucla.edu Tutor: Yeng-Zhong Lee yenglee@cs.ucla.edu

  2. Outline • Introduction • Motivation • Goal • Simulation Design

  3. Introduction • Bluetooth vs 802.11 • Similarities • Radio frequency at ≈ 2.4 - 2.5 GHz • Differences • Power consumption, communication range, price • Frequency hopping spread spectrum = FH-CDMA  DSSS (Direct sequence spread spectrum) = DS-CDMA • Nodes must be organized in Piconets

  4. Bluetooth vs 802.11

  5. Introduction (Cont.) • Bluetooth • No hidden terminal • Piconet • One master, up to 7 slaves, uses frequency hopping code to reduce interference • Master controls access by polling slaves • No slave-slave or master-master communication • Scatternet • Group of piconets connected by gateways • Gateways connect piconets in a scatternet • Gateways use TDD to switch between piconets • TDD (Time Division Duplexing) of gateways left open

  6. Bluetooth Scatternet

  7. Introduction (Cont.) • 802.11, TCP has sometimes been shown to degrade fairness • For 802.11, it has been shown that TCP with window size > 1 only increases collisions, thus degrading throughput • Bluetooth alleviates those problems of collision with separate domains/piconets

  8. Polling Schemes and Gateways • Static-cyclic polling scheme • Slaves are polled in a fixed order in all polling cycles • Flows may consistently capture the bandwidth of others’ due to limited queue for each slave • Flows across the scatternet will contend for the queues of gateways • Fairness issues? • Pseudo-cyclic polling scheme • Slaves are polled in a dynamically decided random order • Piconets coordinate and share gateways according to an agreed superframe cycle; does not allow for pseudo-cyclic polling; must use gateway at allocated time

  9. Our Study • How does TCP behave over Bluetooth? • Focus on Fairness/Capture behavior • Effect of large delays • connections across scatternet through multiple gateways; how good can throughput and fairness be? • large delay vs. short delay; does short delay capture? • Is there a maximum number of gateway hops that a flow can go through while still maintaining a “good” performance of TCP?

  10. Simulation • Glomosim • Bluetooth implementation given to us by tutor • Frequency hopping pattern mechanism allows the overlapping of different piconets in the same space without a significant increase of interference • Structure and TDD are predetermined in configuration files • Use FTP model of connections in Glomosim

  11. Simulation • Assumptions • Masters are full time in piconet and do not become slaves in other piconets • Up to 2 gateways between piconets • Stick to simple topologies of scatternets: linear/chain, ring, and possibly grid • Gateways become bottleneck, routing predictable • Node placement random, in unpartitioned space, with no mobility of nodes

  12. Simulation Throughput between adjacent piconets i and j with one gateway b(i,j) = min( b * fi, b * fi) si + overhead(si) sj + overhead(sj) b = Bluetooth throughput sx = # nodes active when gateway present fx = proportion of time gateway in piconet We prevent FTP connections from having the same sources or destinations, so si = sj, and we set TDM of gateways to ½ & ½ to maximize throughput

  13. Simulation • Different scenarios • Connections with same number of gateway hops vs. longer and shorter connections • Flows going in same direction vs. bidirectional traffic across scatternet • Effect of master vs. slave as source or destination • Lines/chains, rings, grids

  14. Status of Experiment • Analyzing current results • Investigating variations in results caused by simulation environment • Considering more data sets to simulate, variations to try

  15. Future/Ongoing Work: • Smaller packet size • Decrease effects caused by delay? • Buffer size • Smaller buffers’ effect on capture • TCP Congestion window size • How bandwidth is affected by # of gateways • Effectiveness of RED polling schemes • Compare different TCP implementations (Tahoe, Reno, Westwood, …)

  16. Thanks!

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