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Reporter ：黃俊銘

Broadcasting in VANET Tonguz O., Wisitpongphan N., Bai F., Mudalige P., Sadekar V. 2007 Mobile Networking for Vehicular Environments  , vol., no., pp.7-12, 11-11 May 2007. Reporter ：黃俊銘. Outline. Introduction Different Regimes for Broadcasting in VANET

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Reporter ：黃俊銘

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  1. Broadcasting in VANETTonguz O., Wisitpongphan N., Bai F., Mudalige P., Sadekar V.2007 Mobile Networking for Vehicular Environments , vol., no., pp.7-12, 11-11 May 2007 Reporter：黃俊銘

  2. Outline • Introduction • Different Regimes for Broadcasting in VANET • Distributed Vehicular BroadcastProtocol (DV-CAST) • Discussion & Conclusion

  3. Introduction • 在VANET中廣播不同於MANET的路由 • Network topology • Mobility patterns • Demographics • Traffic patterns at different times of the day • 對於大多數車載廣播應用而言，傳統ad hoc路由協定不適用在VANET • DSR • AODV

  4. Different Regimes for Broadcasting in VANET • 三種不同車載運作的機制： • Dense Traffic Regime • 盲目的廣播封包可能會導致在鄰近節點傳輸之間頻繁的爭用和衝突 • Sparse Traffic Regime • 網路重新恢復時間內，可能導致幾秒鐘到幾分鐘分開的車輛之間訊息傳遞 • Regular Traffic Regime • 不是每台車輛看到相同的區域拓樸，例如：有些車輛可能很少鄰居，有些可能很多鄰居

  5. Dense Traffic Regime • BroadcastSuppressionTechniques

  6. Packet Loss Ratio

  7. Total Delay

  8. Normalized Packet Penetration Rate

  9. Dense Traffic Regime • 從上可以觀察到，slotted p-persistence方法能以些微增加總延遲與減少滲透率作為代價來大幅減少封包遺失率

  10. Sparse Traffic Regime

  11. store-carry-forward Average per-gap re-healing time

  12. Distributed Vehicular Broadcast Protocol (DV-CAST) • 在設計DV-CAST協定，做了以下假設： • 基礎架設是不可用 • 每輛車有全球定位系統(GPS)和無線通訊設備 • 使用基本的逐跳( per-hop )路由方法，其中只使用區域連結性資訊( 1-hop neighbor topology )來做出路由判斷 • 每輛車不斷檢測他的區域連結性，在封包到達到時間時以確定車輛運作在哪一個狀態下

  13. DV-CAST Protocol • 路由參數： • Message Direction Connectivity (MDC) • 確定他在群組/群集中是否是最後的車輛 • Opposite Direction Connectivity (ODC) • 確定他在相反的方向中是否至少有一輛車被連結到 • Destination Flag (DFlg) • 作為來源移動在相同的方向中，確定他是否是預期的訊息接收者

  14. Decision Tree for DV-CAST Protocol

  15. Case Ⅰ：Well-Connected Neighborhood • 如果車輛至少有一個鄰居在訊息轉發方向(MDC=1)，車輛被認為在連結良好的鄰居區域中 • 使用Dense Traffic Regime的方法

  16. Case Ⅰ：Well-Connected Neighborhood • 在群組1中每輛車除了A是在這群組中最後一台車輛外(MDC=0)，廣播來自S的訊息時，將會標記為<MDC =1, ODC = 1/0, DFlg = 1> • 除了B外，群組3的車輛也會有類似的標記 <MDC = 1, ODC = 1/0, DFlg = 0> • 除了A和B外兩個群組的每台車輛將適用broadcast suppression algorithm

  17. Decision Tree for DV-CAST Protocol

  18. CaseⅡ：Sparsely-Connected Neighborhood • 如果在群集中車輛是最後一台，車輛是運作在sparse traffic regime中，如下圖車輛A和B

  19. CaseⅡ：Sparsely-Connected Neighborhood • 如果在相反的方向中至少有一個鄰居，在這機制中車輛被認為是在連結稀疏的鄰居區域，如下圖車輛A和B • 這些車輛的參數將被設置為<MDC =0, ODC = 1, DFlg = 0/1>

  20. Decision Tree for DV-CAST Protocol

  21. Case Ⅲ：Totally Disconnected Neighborhood • 車輛運作在sparse traffic regime中，如果在訊息轉發的方向中沒有鄰居且在相反向中沒有連結任何車輛，車輛被認為是在完全斷開的鄰居地區

  22. Case Ⅲ：Totally Disconnected Neighborhood • 群組3和群組2被車輛A斷開，標記將設置為<MDC = 0, ODC = 0, DFlg = 1>

  23. Decision Tree for DV-CAST Protocol

  24. Discussion & Conclusion • 在不規則的拓樸結構中(高速公路出口或市區)可能需要附加的資訊(如GPS路線) • 區域拓樸結構的資訊準確性可能導致協定失敗 • 提出DV-CAST協定在VANET中可以有效應用在傳輸及安全上

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