Research And Implementation Of Modularized Transmission Control Protocol Based On NGN

Large-scale interactive applications have demanding requirements on underlying transport protocols for efficient dissemination of real-time multimedia data over heterogeneous networks.Existing transmission control protocols fail to meet these requirements due to following reasons: 1) recent trend of distributed applications include both discrete media (such as texts and graphics) and compositive media (such as audio and vedio) .The transmission of These media data units is inconstant;2) protocols that support multiple concurrent sources only have limited scalability;3) few of them have implemented end-to-end TCP-friendly congestion control;4) Most of protocols have defects in capability of service and configuration of quality of service. This dissertation presents a modularized transmission control protocol that addresses all of above issues.Firstly,instead of following the traditional end-to-end model for unicast,the Modularized Transmission Control Protocol (MTCP) takes the original TCP into a group of protocol objects,and each object is encapsulated as a function model as following:connection management module,which is used to manage the setup, constain and maintenance of the connection;input and output module are in charge of sending and receiving of data;the management of flow and degressive of acceleration, slow start, fast retransmission and fast recovery are completed by flow and congestion control module;there are also timing and computing modules which are used to compute the RTT and maintain the timers;the input state module is the last one that is dispoing of the TCP state machine when hosts receive data.Secondly,the protocol also modifies the original TCP congestion control algorithms.We analyze the reversed effect of delayed acknowledge in slow start period,the effect of initial little windows to TCP slow start time and throughputin detail.We do research into the problem that congestion windows decrease because of retransmission brought with the out of sequence packets,delayed packets and unnecessary timeout retransmission,these problems reduce the efficiency throughput of TCP connection.In implementation of congestion control algorithms,we improve the conventional congestion control algorithms with dynamic delay timer,the bigger initial windows,quick acknowledge in slow start period and undo processing of decrease congestion windows,which enhance the real time performance and decrease the reverse effect to throughput.Thirdly,it has expandable application programming interface.In contrast to BSD Sockets,the new one modifies more special features such as:oriented-object design, service data transmission based on message, supporting multiple hosts service, data resending, symmetric socket options and new socket features.All these are suitable for the communication system which supports multimedia and service configuration.To demonstrate the efficacy of our approach to supporting large-scale interactive applications, we have implemented a network multimedia conferencing tool, on top of MTCP.It is essentially an enhanced whiteboard application that supports cooperative Web browsing and audio/video communications, which can be used in real-timeconference for innovating the traditional conference mode.