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Multi-Path Multimedia Transmission in Ad-hoc Networks Related Work

Multi-Path Multimedia Transmission in Ad-hoc Networks Related Work

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Multi-Path Multimedia Transmission in Ad-hoc Networks Related Work

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  1. Multi-Path Multimedia Transmission in Ad-hoc NetworksRelated Work Marcin Michalak michalak@iam.unibe.ch

  2. Agenda • ad-hoc networks • multi-path • routing • content • experimental results • references • summary

  3. Environment • ad-hoc networks – no infrastructure, multihop, multi-path, mobile, wireless • users want good quality • real need for QoS – network may get congested • not much to rely on…

  4. Important parameters • delay (~ no. hops) • jitter • available bandwidth • stability of path • packet error rate • congestion ad-hoc: all variable

  5. Multi-Path • independent paths - independent loss probability “it has been observed that for multi-path transmission the end-to-end application sees a virtual average path which exhibits a smaller variability in quality than any of the individual paths”  more is better • how to do it?: • routing issue – getting multiple paths • content issue – dividing content

  6. Multipath Routing • Current algorithms already provide information about multiple routes, but only use one at a time • Transmission: • redundant: data + error correction • non-redundant: all paths transmit data • some promising work on Internet, using relays • load balancing (but interference) • still a very open issue

  7. Path Selection • correlation factor: no. of links connecting 2 paths • paths should be unrelated, to avoid interference (sharing same link): a) two node-disjoint, unrelated paths b) node-disjoint, 7-related c) link-disjoint node-

  8. shared-channel model the larger c.f., the larger delay – interference Path Selection (2) • Path should be: • node-disjoint • short • have small correlation factor

  9. Experimental Results • 50 nodes • 1500m x 500m field • 900s simulation time • TX range 250m • speed 5-10 m/s • CBR: 512B / 250ms • pause time 0-900 s • delay including queue • and propagation improvement limited under pause time 300s

  10. SMR – Split Multipath Routing • Sung-Ju Lee (HP) and Mario Gerla (UCLA) • on-demand discovery • using request/reply cycles • goal: build maximally disjoint paths • 2 routes: shortest delay + max disjoint (shortest hop) • source routing • per-packet allocation

  11. SMR - Simulation • SMR-1: route recovery when any of the routes is invalidated • SMR-2: only when both are invalidated • comparison to DSR – single path

  12. GloMoSim 50 mobile hosts (1000 m)2 area prop. range 250m channel 2Mbps run 300 sec speed 0-10 m/s SMR – Packet Delivery Rate SMR-2 SMR-1 DSR simulation ends on 300 s....

  13. SMR – End-to-End Delay • 300 s seems to be a limit? • DSR uses longer paths DSR SMR-1 SMR-2

  14. Coding possibilities • Single Description • Reference Picture Selection (RPS) – from H263+ • Multiple Description (MD) • layered coding (+ARQ) – good for mcast • Video Redundancy Coding

  15. Multiple Description Coding (MDC) • Code video into a number of descriptions, each of roughly equal importance • Properties: • receiving either bitstream gives good quality • receiving both bitstreams gives highest quality Good Quality Video Decoder 1 Stream 1 Original Video MD Coder Highest Quality Video Decoder 2 Stream 2 Good Quality Video Decoder 3 (from HP slides – John Apostolopoulos)

  16. Results (Panwar ...) • MD coding works well for low-error links • Layered Coding + ARQ is better for high-error links, but increases delay Average PSNR of Decoded Images (dB)

  17. References • “Split Multipath Routing with Maximally Disjoint Paths in Ad hoc Networks”, Sung-Ju Lee & Mario Gerla • “Real-Time Voice Communication over the Internet Using Packet Path Diversity”, Liang, Steinbach, Bernd Girod, Stanford University • “On-Demand Multipath Routing for Mobile Ad Hoc Networks”, Kui Wu and Janelle Harms, University of Alberta • “Video Transport over Ad-hoc Networks Using Multiple Paths”, S.Lin, Y.Wang, S.Mao and S.Panwar

  18. Summary • multi-path transmission seems to be a good solution – better quality, lower average delay • not only for multimedia • several video coding techniques • many issues still open

  19. Questions? • is this all as good as presented? ?