為了在車載網路環境下實現可靠傳輸，此篇論文提出了分段式可靠傳輸協定。分段式可靠傳輸協定的基本想法，是將一條長的連線分割為數段子連線，以減少封包傳輸對網路的額外消耗，每一段子連線的長度則取決於網路狀態。分段式可靠傳輸協定必須解決三個主要問題，(1)當連線建立時，如何決定每段子連線的長度、(2)當連線建立後，如何增進連線的穩定度，以適應車載網路環境之網路布局的快速變動，以及(3)如何解決網路壅塞。分段式可靠傳輸協定使用了一個估測方法，它使用車輛的位置和速度資訊來估測兩車之間的預期連線壽命。這個估測方法可以用來決定並且動態調整子連線的長度。本論文並提出了另一個方法，名為頻道使用率感知的壅塞避免機制。這個機制可以避免隨意網路環境的壅塞。在頻道使用率感知的壅塞避免機制中，每個節點的無線頻道使用率可以用來參考以調整傳輸速度，進而避免壅塞。模擬的結果顯示，分段式可靠傳輸協定可以在車載網路環境中順利運作。而且妥善地解決前述的三個問題。

To have reliable transmission in the VANET environment, a Split Reliable Transport Protocol (SRTP) is proposed in this thesis. The basic idea of SRTP is to separate a long connection into several sub-connections in order to reduce the overhead of packet retransmission, in which the length of each sub-connection depends on links’ states between vehicles. Three main issues that need to be resolved for SRTP are (1) how to decide the length of each sub-connection when a connection is established initially, (2) how to enhance the connection’s stability after the connection is established to deal with the fast topology change in the VANET environment, and (3) how to deal with packet congestion. An estimative scheme using location and speed information of vehicles to estimate the connectivity time of the links between vehicles are used in SRTP. The estimated values can be used to decide the lengths of sub-connections and adjust them dynamically. Another mechanism named Channel Busy Rate Aware (CBRA) congestion avoidance is proposed to avoid network congestion in the ad hoc network environment. In CBRA, busy rate and utility rate of the wireless channel for every node are used to adjust the source’s transmission rate and to avoid congestion. The simulation results show that SRTP can be operated well in the VANET environment and the aforementioned three issues can be appropriately resolved.

[1] Brodsky, M. Z., and R. T. Morris (2009), “In defense of wireless carrier sense”, in SIGCOMM.
[2] Cordeiro, C. de M., S. R. Das, and D. P. Agrawal (2002), “COPAS: Dynamic Contention-Balancing to Enhance the Performance of TCP over Multi-hop Wireless Networks”, in Proceedings of the 11th IEEE International Conference on Computer Communication and Networks, pp.382~387, Miami, FL, USA, October.
[3] Dutta, A., D. Saha, D. Grunwald, and D. Sicker (2009), “SMACK: a SMart ACKnowledgment scheme for broadcast messages in wireless networks”, in SIGCOMM.
[4] Floyd, S., and V. Jacobson (1993), “Random Early Detection Gateways for Congestion Avoidance”, IEEE/ACM Transactions on Networking, 4(1) pp.397~413.
[5] Fu, Z., P. Zerfos, H. Luo, S. Lu, L. Zhang, and M. Gerla (2003), “The Impact of Multihop Wireless Channel on TCP Throughput and Loss”, In Proceedings of the 22nd Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM), Vol. 3, pp.1744~1753, Sun Francisco, USA, March 30~April 3.
[6] Gollakota, S., S. D. Perli, and D. Katabi (2009), “Interference alignment and cancellation”, in SIGCOMM.
[7] Gupta, S., C. Hunter, P. Murphy, and A. Sabharwal (2009), “Warpnet: Clean slate research on deployed wireless networks”, in Mobihoc, 2009.
[8] Joo, C. X. Lin, and N. B. Shro (2009), “Understanding the capacity region of the greedy maximal scheduling algorithm in multihop wireless networks”, 4(17), pp.1132~1145, IEEE/ACM Transactions on Networking.
[9] Kopparty, S., S. Krishnamurthy, M. Faloutsos, and S. Tripathi (2002), “Split-TCP for Mobile Ad Hoc Networks”, In Proceedings of the IEEE Global Telecommunications Conference (GLOBECOM), pp.17~21, Taipei, Taiwan, R.O.C., November.
[10] Sen, S., R. Roy Choudhury, and S. Nelakuditi (2010), “Csma/cn: carrier sense multiple access with collision notication”, in MobiCom.
[11] Warrier, A., S. Janakiraman, S. Ha, and I. Rhee (2009), “DiQ: Dierential Backlog Congestion Control for Multi-hop Wireless Networks”, in INFOCOM.
[12] Wu, K., H. Tan, Y. Liu, J. Zhang, Q. Zhang, and L. Ni (2010), “Side channel: bits over interference”, in MobiCom.
[13] Xu, K., M. Gerla, L. Qi, and Y. Shu (2005), “TCP Unfairness in Ad Hoc Wireless Networks and a Neighborhood RED Solution”, Wireless Networks, 4(11), pp.383~399.
[14] Ye, Z., S. Krishnamurthy, and S. Tripathi (2004), “Use of Congestion-Aware Routing to Spatially Separate TCP Connections in Wireless Ad Hoc Networks”, In proceedings of the 1st International Conference on Mobile Ad Hoc and Sensor Systems (MASS), pp.389~397, Fort Lauderdale, Florida, October 25~27.
[15] L. Yang, B. Y. Zhao, and H. Zheng (2010), “The spaces between us: setting and maintaining boundaries in wireless spectrum access”, in MobiCom.
[16] Transmission Control Protocol, IETF RFC 793, 1981
[17] Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE Stsndard 802.11, 1999.
[18] IEEE Std. "IEEE Standard for Wireless Access in Vehicular Environments (WAVE)—Multi-channel Operation", February 2011
[19] “Network Simulator”, http://nsnam.isi.edu/nsnam/index.php/Main_Page
[20] “Normal Distribution”, http://mathworld.wolfram.com/NormalDistribution.html