Sven Bittner, 13 April 2004 Institute of Computer Science Freie Universität Berlin - PowerPoint PPT Presentation

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Sven Bittner, 13 April 2004 Institute of Computer Science Freie Universität Berlin

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  1. Talk at the Workshop on Wireless Information Systemsat the Conference ICEIS Ordering in Mobile NetworksUsing Integrated Sequencers Sven Bittner, 13 April 2004 Institute of Computer Science Freie Universität Berlin bittner@inf.fu-berlin.de

  2. Motivation • Distributed applications (ISs, replication, CSCW) use group communications (e.g. multicast) • Systems expanded to mobile environments • Wired networks: • Delivery trees only for delivery • Sequencers for ordering • Wireless networks: vector clocks and matrices • Bad scalability • Enhance and extend wired algorithms to suit mobile environments Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  3. Roadmap • System Model • Algorithms • Ordering • Dynamics • Mobility • Performance Evaluation • Conclusions & Outlook Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  4. Roadmap • System Model • Algorithms • Ordering • Dynamics • Mobility • Performance Evaluation • Conclusions & Outlook Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  5. System Model (1) • Mobile Support Stations (MSS, S = {S1,S2,…,Sn}) • Fixed wired network (reliable and FIFO) • Acyclic graph in application layer (no restriction in case of link errors) • Mobile Hosts (MH, H = {h1,h2,…,hx}) • Connected to 1 MSS (local MSS S (hx)) • All communications via local MSS • Connections reliable and FIFO System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers


  6. MHs reg. for gx gx gx gx gx gx Sequencer of gx gx gx gx gx gx gx gx System Model (2) • Multicast Groups (MG, G = {g1,g2,…,gx}) • Closed groups: only send to registered groups G (hx) • Sequencers (located on MSSs) • One per MG • integrated components  no extra cost • Direction sufficient to know for MSSs • Delivery • MSSs know MGs from local MHs • MSSs exchange information about MH’s MGs  Direction of MHs of MGs sufficient System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  7. Roadmap • System Model • Algorithms • Ordering • Dynamics • Mobility • Performance Evaluation • Conclusions & Outlook Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  8. mx my my mx Algorithm – Causal Order • Between multiple groups • Side-effect from tree-based overlay and FIFO mx arrived (and is delivered) before my in all nodes mx my System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  9. MHs reg. for gx mx mx√ mx mx√ mx√ mx√ mx√ mx√ mx√ Algorithm – Total Order • Within each group • Send unmarked message to sequencer Sx via MSSs • Sequencer sends marked message to all neighbors • Deliver marked message to MHs Sequencer of gx System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  10. Algorithm – Causal & Total Order • Problem • Destruction of multiple group causal order by different sequencers • Delivery of causally related messages depends on the path from the sequencer • Solution • Local MSSs delay messages until last (causally preceding) arrived at sender  Causal order between multiple groups and total order within each group System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  11. Algorithm – Dynamics & Mobility • Sequencer movement (from Sx to Sy) • Claim: located in central network position • Count messages from neighbors • Moving is transparent to other nodes • Dynamic groups (offline/online) • Register/deregister at local MSS • Update forwarding information • Handoff (hx moves from Sx to Sy) System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  12. Roadmap • System Model • Algorithms • Ordering • Dynamics • Mobility • Performance Evaluation • Conclusions & Outlook Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  13. Performance Evaluation • Evaluate performance of network of MSS • Represented by time to deliver a multicast • Symmetric network, density parameter ρ - no. of subordinate MSSs (ρ=3, 4 levels) • Simulation using OMNeT++ • Uniform distribution of MHs • 1 multicast group System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  14. Performance Evaluation – MSSs/MHs • Sequencer in central network position, ρ=3 • Significant decrease • More MSSs  less delivery time • 67 to 136 times faster • Linear increase (constant extra-work per MH) • 12 to 19 times slower System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  15. Performance Evaluation – Sequencer • 10 level of MSSs, ρ=2 (all) – MHs at all MSSs (outer) – MHs on outer level (inner) - MHs on 7 inner levels • Central position  best results • Up to 21% performance increase • Best: (outer) • 4 times as much MHs as in (inner), but faster delivery • Reason: inner MSSs not involved in delivery • Worst: (inner) • 8 times less MHs as in (all), but same delivery time • Reason: inner MSSs always same load System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  16. Roadmap • System Model • Algorithms • Ordering • Dynamics • Mobility • Performance Evaluation • Conclusions & Outlook Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  17. Conclusions & Outlook • System model • Integrated sequencers, acyclic overlay network • Algorithms for ordering, sequencer movement, changing groups and disconnections, handoffs • Claim: sequencer in central position • Evaluation • Best results in central position • Future work • Evaluate handoffs and movement itself System Model Algorithms Performance Evaluation Conclusions Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers

  18. Thank you for your attention! Contact: Sven Bittner, bittner@inf.fu-berlin.de Sven Bittner - Ordering in Mobile Networks Using Integrated Sequencers