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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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