Transmission Control Protocols Over Wired/Wireless Hybrid Networks

With the rapid development of wireless technology,wireless networks have become the important part of Internet.Packet loss as a result of factors other than congestion impact the performance of TCP in wired/wireless hybrid networks,which include the disconnection of wireless media at physical layer,the access failure at MAC layer,routing change at network layer,and so on.Traditional TCP protocols use all packet loss as the indicator of congestion and decrease the sending rate unnecessarily.As a result,TCP performance degrades in wired/wireless hybrid networks.Most existing TCP protocols are designed for some single network circumstances.With respect to hybrid networks composed of heterogeneous networks,problems that how to keep transmission efficiency have not been solved in a satisfactory way.Considering these problems,this paper focuses on how to improve performance of transport control protocol over wired/wireless hybrid networks.The main approaches are packet losses differentiation, congestion perception and cross-layer design.Main contributions of this paper include:1.Presenting an adaptive loss differentiation algorithm based on queue management,A_BQM,which can adptively adjust the method of match the loss character on midrouters.Simulation results show that A_BQM can obtain higher differentiation accuracy and simpler implement than BQM.2.Presenting a congestion perception method,CP_ECN,which calculates congestion probability based on several ECN feedbacks.It can infer network states in a more reasonable way.Both examples and simulations indicate that the predictions of CP are corresponding to real situations in hybrid networks.3.Applying CP_ECN into two TCP protocols,Reno and Westwood. Their performances are evaluated in network simulations and a Linux testbed of hybrid networks.Results show that they can improve transmission efficiency and protocols by using CP_ECN method is of good fairness and friendliness.4.Presenting a cross-layer ECN scheme that feedbacks congestion information at MAC layer to TCP senders.This scheme extends congestion conception to lower layer of networks.Subsequently it can cooperate with existing ECN feedback at IP layer and optimize congestion congtrol over wired/wireless networks.5.Presenting a soluation based on cross-layer ECN as to the unfaimess problem when wireless nodes are different hops away from access point.Since our solution is based on the congestion control scheme,it can distribute network resource efficiently and fairly. Compared with existing schemes,our solution can obtain higher throughput and fairness in the same time.Only error control with high quality and losses differentiation algorithms can assure transmission efficiency in hybrid networks.More precise congestion perception and cross-layer designed optimizing can improve QoS in hybrid networks.This paper focuses on hereinbefore aspects,proposes practical approaches and obtains anticipated achievements.Researches of this paper can promote development of wireless accesse networks.As these approaches are applied into mobile productions in the future,they can resist bad circumstance of wireless links and provide services more abundantly and more steadily.