opensourcejason.info
mobi share session 1

CodeTorrent

  • Multimedia-based proximity marketing
  • Movie trailers in nearby theatres
  • On VANET
  • Based on BitTorrent file swarming from same group called CarTorrent
  • Noted limitation: Missing coupon problem
    • Use network coding to solve problem
  • Basic CarTorrent Idea:
    • Single-hop puling instead of CarTorrent multihop
    • Cars exchange randomly combined packets
  • They share our belief on single-hop vs. multi-hop routing in ad-hoc (i.e., single hop is better)
  • Networking coding
    • Matigate rare pice problem
    • maximize benefits of overhearing
  • Periodic beaconing for discovering helpful nodes (who has at least one LI encoded block)
  • Simulation in QualNet using real-track mobility model
  • CodeTorrent
    • scales to mobility
    • favors cooperations
    • eliminate missing coupon problem
  • Future work
    • model impact of mobility
    • real testbed.

XScribe

  • P2P can be a booster for MANET deployment
  • Efficient P2P services are a more friendly environment (zero-conf)
  • Designed around opposite assumption
    • P2P: scale to thousands of users
      • resource-rich environemnt
      • trade consumption for scalability
    • MANET
      • hundreds of nodes are unreasonable
      • resource-scarce
      • rade everything for reduce bandwidth consumption
  • P2P over MANET
    • legacy typically fails, but it's feasible, and worth it
    • success: CrossROAD, VRR
  • Legacy P2P: Scribe
  • multicast protocol working on top of a Pastry-like DHT
  • straightforward to use structured overlays for mcast
  • build shared tree based on a standard reverse-path algorithm
  • implemented on top of overlay, subject-based routing identifies root and builds tree
  • self-organizing, self-healing, decentralized
  • scribe data delivery: get everything to the root
  • cons
    • centralized
    • several hops in the overlay
  • XScribe
    • tries to address centralization/structure issues (avoid synchronization)
    • avoid serveral-hop problem
    • pure p2p (overlapping path exploitation) not addressed
  • make all nodes in the group aware of receiver set
  • send send a distinct mesage to each receiver
  • Used core ideas of CrossRoad (pastry-based DHT) to make receiver awareness efficient
  • embed group membership into L3 routing ads
    • no extra MAC-level access
  • CrossROAD makes all nodes just one-hop away from each other
  • Experiments
    • Collaborative whiteboard application
    • packet loss halved on most nodes (xscribe vs. scribe)
    • slight increase on some nodes
    • significant delay decrease
  • Conclusion
  • solve Scribe problems of centralization and structure-induced path stretch by efficient dissemination of group membership and using CrossROAD-based ideas to avoid path stretch
  • Critique
    • Trend of performance worsening with load is not fixed
  • Lesson learned
  • pure p2p delivery is not affordable in MANET
  • p2p mcast has to meet L3 mcast
  • Audience question:
    • Xscribe seems to be a one-hop overlay based on OLSR, but there is already mcast work in OLSR, why is it not compared.
    • What about scalability?
      • Response: goal 20-30 to nodes because of flat-ad-hoc limitation
    • Followup: Is this scheme worth it with such a small network?

GUESS

  • Assumed biggest limitation: spectrum availability
  • Shows typical FCC allocation image
    • Observation: paid-for spectrum is unused in many areas
  • Opportunistic Spectrum Sharing: OSS
    • Already legislatd for a small section of 5Ghz
    • proposed for VHF/UHF
    • Requires smart sensing radios that dynamically tune
  • This paper focuses on sensing available medium
  • Observation: Primary user detection is non-trivial (shadowing)
    • Solve it via coordination approach between secondary users
  • Requirements:
    1. Large amount of sensory data
    2. Short timescale (need quick decisions)
    3. Minimal overhead
  • First-order approach:
    • exchange complete info with all devices (structure-based)
    • Communicate periodically
    • not robust to failure and change
    • may be excessive
  • Spectrum Sensing Obersation
    • summaries are sufficint for coordination
    • compute statistics for a band
      • Idea 1: In-network aggregation
  • spectrum usage changes incremenationally
    • no need for periodic recompute, energy changes slightly over time
      • Ideas 2: We need update protocl
  • Contributions
    1. Novel application of randomized gossip to spc sensing
    2. Apply probablistic F-M algorithm for aggregation
    3. Extend system to support incremental updates
  • Aggregation issues
    • duplicate messages
    • large message size
    • Solution:
      • F-M bit-vector approach (probabilistic summaries, sorta like lossy compression)
  • F-M COUNT extended to SUM by varying "coin toss" depending on signal strength (more for higher)
  • roblem: F-M aggregate can not be updated
    • Basic sol: maintain an addition F-M delete vector for descrease in value
  • Finally: Incremental Random Walk Info exchange protocol
    • Only initiate random walks from nodes with new info
  • Inc random walk converges up to almost 3 times faster in simulation
    • See 2.5x reduction in overhead
  • Future work:
    • limit impact on distant nodes
    • Avoid minor updates
    • Implentation considerations (DNE yet)
  • Audience Question:
    • Why is this important over 1000 nodes
      • answer: that's the extreme density case
    • Question: can you also use long term statistics?
      • Answer: yes, for fixed infrastructure/environment
    • Question: how do you handle biasing because you use bit aggregate
      • Answer: some things addressed in the paper (multiple