Research On The Performance Of TCP Over Wireless Mobile Ad Hoc Networks

Transmission Control Protocol - TCP is one of the most important network protocols, however, the performance of TCP over wireless mobile Ad Hoc networks (MANET) is damaged, such as goodput, stability, fairness and security. The reasons of performance decline come from some problems in MANET, such as the bit error rate and loss rate of the channel, the contention and collision of the media access layer, the mobility of nodes, the congestion and security etc. The state of art protocol improvement schemes for TCP over MANET always focus on one problem, so the general scheme is still on research. For the application in heterogeneous networks, the end-to-end TCP enhancement scheme is more significant to research.For the improvement of the TCP goodput performance over multihops wireless networks, an end-to-end combination scheme - TCP-CD, including the limit of sending window and delayed ACK mechanism is adoptable. The sending window size is recommended to set to 2 MSS (Maximized Size Segment). The simulation results show it outperforms single scheme. Considering the impact of routing protocol and mobility model to the TCP performance, for the improvement of TCP performance over mobile ad hoc networks, TCP-CDR scheme is proposed, which includes TCP-CD and the maximized retransmission timeout limit. After the comparisons with the state of art end-to-end TCP improvement scheme, such as FeW and TCP-AP, TCP-CDR has better performance than other schemes both in the Random Waypoint mobile scenarios and Social Network mobile scenarios.For the TCP stability over MANET, the analysis find that when TCP over multihops wireless network, the hidden terminal will lead to a large amount of MAC packet dropping owing to the collision. It results in the exceeding of retransmission retry times in MAC layer and packet dropping, so that the TCP DATA or ACK packet will be loss. TCP sender always goes into Slow Start phase and the stability is declined. To deal with this problem, it is not effective only to limit sending window size. Delayed Ack scheme is also required. The general discussions including formal description of TCP stability problem and quantitive analysis of hidden terminal points out the reason of TCP stability.For the TCP fairness over wireless cum wired networks, the scheme of setting limit of TCP sending window size is proposed and evaluated to improve the TCP fairness between upload and download flows in wired cum wireless networks. For the TCP fairness over MAENT, the analysis of the reason of TCP unfairness and the classification of possible scenarios that have impacts to the fairness are also given. Fairness is better between overlapped TCP flows. For none-overlapped TCP flows, only all nodes in TCP flows are in the interference range can maintain TCP fairness. If one TCP sending node is the hidden terminal of the sending node in another TCP flow, the unfairness will be greatest. To resolve this problem, 802.11e is recommended to improve the TCP fairness for that the priority of the one hop TCP flow can be set to a low value. The accumulative fairness index and instant fairness index are the metrics of TCP fairness in MANET.Performance is always with the consideration of security, congestion targeted TCP RoQ (Reduction of Quality) DDoS attacking schemes are classified into four categories: Pulsing attacking, Round Robin attacking, Self-whisper attacking and Flooding attacking. The defense scheme includes detection and response. Detection signals include RTS/CTS packets receiving frequency, channel sensing busy (signal interference) frequency and RTS/DATA retransmission times. The response scheme includes ECN (Explicit Congestion Notification) marking mechanism.