A novel method which can detect the possible handoffs for mobile nodes is proposed in this article. The method can be deployed on mobile nodes. So when a possible handoff occurs, mobile nodes can detect and take some ...A novel method which can detect the possible handoffs for mobile nodes is proposed in this article. The method can be deployed on mobile nodes. So when a possible handoff occurs, mobile nodes can detect and take some necessary actions in time. In this study, the method is also used to optimize the transmission mechanism of Q-TCP. Moreover, the simulation results show that Q-TCP can provide better quality of service （QoS） for mobile nodes when they are moving among different agents.展开更多
Researchers have used extensive simulation and experimental studies to understand TCP performance in wireless multihop networks. In contrast, the objective of this paper is to theoretically analyze TCP performance in ...Researchers have used extensive simulation and experimental studies to understand TCP performance in wireless multihop networks. In contrast, the objective of this paper is to theoretically analyze TCP performance in this environment. By examining the case of running one TCP session over a string topology, a system model for analyzing TCP performance in multihop wireless networks is proposed, which considers packet buffering, contention of nodes for access to the wireless channel, and spatial reuse of the wireless channel. Markov chain modelling is applied to analyze this system model. Analytical results show that when the number of hops that the TCP session crosses is ?xed, the TCP throughput is independent of the TCP congestion window size. When the number of hops increases from one, the TCP throughput decreases ?rst, and then stabilizes when the number of hops becomes large. The analysis is validated by comparing the numerical and simulation results.展开更多
A scheme of setting a limit to the TCP sending window size is proposed to improve the TCP fairness between upload and/or download flows in wired-cum-wireless networks. The goodput and delay of the upload and download ...A scheme of setting a limit to the TCP sending window size is proposed to improve the TCP fairness between upload and/or download flows in wired-cum-wireless networks. The goodput and delay of the upload and download TCP flows arc compared to evaluate the TCP fairness for different schemes, which are the different combinations of setting a limit （64 or 4） to the sending window size and using the delayed acknowledgement （ACK） scheme or not. Extensive simulation results and analysis show that （ 1 ） for TCP download flows, setting the limit of sending window size to 4 can improve the fairness; （2） for TCP upload flows, limiting the sending window size and using the delayed ACK strategy are both beneficial to fairness; （3） for TCP download and upload mixture flows, limiting the sending window size to a small value （ e. g. , 4） rather than using the delayed ACK strategy, is the solution to improvement of the fairness ; （4） a large delay interval （200 ms or 300 ms） does not result in improvement in fairness and performance; （ 5 ） a larger TCP packet size （ 1400 B） can improve the TCP upload goodput and decrease the download goodput; in contrast, a smaller TCP packet size （560 B） can increase the download goodput and decrease the upload goodput.展开更多
Transmission Control Protocol (TCP) was originally designed for wired networks. Many compatibility problems exist when it is applied to wireless environments, and hence it needs to undergo modifications. Currently, th...Transmission Control Protocol (TCP) was originally designed for wired networks. Many compatibility problems exist when it is applied to wireless environments, and hence it needs to undergo modifications. Currently, there are several TCP performance enhancement techniques for application of TCP in wireless environments, but all of them conflict with IPsec. This paper not only analyzes these conflicts, but also proposes 4 solutions: replacing IPsec with Transport Layer Security/Secure Socket Layer (TLS/SSL) protocol, adopting the extended Encapsulating Security Payload (ESP) protocol, segmenting the TCP route, and modifying the end-to-end protection mode of IPsec. It also presents their strengths and weaknesses.展开更多
文摘A novel method which can detect the possible handoffs for mobile nodes is proposed in this article. The method can be deployed on mobile nodes. So when a possible handoff occurs, mobile nodes can detect and take some necessary actions in time. In this study, the method is also used to optimize the transmission mechanism of Q-TCP. Moreover, the simulation results show that Q-TCP can provide better quality of service （QoS） for mobile nodes when they are moving among different agents.
文摘Researchers have used extensive simulation and experimental studies to understand TCP performance in wireless multihop networks. In contrast, the objective of this paper is to theoretically analyze TCP performance in this environment. By examining the case of running one TCP session over a string topology, a system model for analyzing TCP performance in multihop wireless networks is proposed, which considers packet buffering, contention of nodes for access to the wireless channel, and spatial reuse of the wireless channel. Markov chain modelling is applied to analyze this system model. Analytical results show that when the number of hops that the TCP session crosses is ?xed, the TCP throughput is independent of the TCP congestion window size. When the number of hops increases from one, the TCP throughput decreases ?rst, and then stabilizes when the number of hops becomes large. The analysis is validated by comparing the numerical and simulation results.
基金The National Science Foundation of Chi-na (No.90412010)the Major State Basic Research Devel-opment Program of China(973 Proguam) (No.2003CB317003)
文摘A scheme of setting a limit to the TCP sending window size is proposed to improve the TCP fairness between upload and/or download flows in wired-cum-wireless networks. The goodput and delay of the upload and download TCP flows arc compared to evaluate the TCP fairness for different schemes, which are the different combinations of setting a limit （64 or 4） to the sending window size and using the delayed acknowledgement （ACK） scheme or not. Extensive simulation results and analysis show that （ 1 ） for TCP download flows, setting the limit of sending window size to 4 can improve the fairness; （2） for TCP upload flows, limiting the sending window size and using the delayed ACK strategy are both beneficial to fairness; （3） for TCP download and upload mixture flows, limiting the sending window size to a small value （ e. g. , 4） rather than using the delayed ACK strategy, is the solution to improvement of the fairness ; （4） a large delay interval （200 ms or 300 ms） does not result in improvement in fairness and performance; （ 5 ） a larger TCP packet size （ 1400 B） can improve the TCP upload goodput and decrease the download goodput; in contrast, a smaller TCP packet size （560 B） can increase the download goodput and decrease the upload goodput.
文摘Transmission Control Protocol (TCP) was originally designed for wired networks. Many compatibility problems exist when it is applied to wireless environments, and hence it needs to undergo modifications. Currently, there are several TCP performance enhancement techniques for application of TCP in wireless environments, but all of them conflict with IPsec. This paper not only analyzes these conflicts, but also proposes 4 solutions: replacing IPsec with Transport Layer Security/Secure Socket Layer (TLS/SSL) protocol, adopting the extended Encapsulating Security Payload (ESP) protocol, segmenting the TCP route, and modifying the end-to-end protection mode of IPsec. It also presents their strengths and weaknesses.
