Research On Transport Prptocols Of Next Generation Internet Architecture

The rapid development of mobile and wireless communication technologies is driving the great transformation of modern information society. New markets for mobile computing equipments and wireless network products are increasing and the traditional computer networks are changing into wired-wireless hybrid network. The developments and researches are focused on various wireless network systems and applications, such as WLAN, Bluetooth, UMTS, Satellite, 3G cellular, WSN etc. Mobile terminals become more and more smaller, more and more cheaper, more and more easy-using. At the same time, plentiful applications and services are provided for wireless networks. All these factors are inspiring the development of wireless systems. The incomparable advantages of wireless communication technologies lead the traditional Internet merging various wireless network systems into next generation wireless Internet.Transport protocol layer lies in the middle of OSI seven-layer protocol architecture which plays the most important role of the OSI seven layers. It is the only layer that is responsible for data transmitting and controlling as a whole. The main function of transport protocol is to provide end-to-end transmission services to a session or a connection. There are types of transmission services: connect-oriented service and non-connect-oriented service.. Transport protocols are also responsible for multiplex, traffic control, error control and recovery. Some transport protocols have been standardized and used in the majority network equipments, such as TCP, UDP and RTP/RTCP while some protocols have been proposed and researched such as SCTP, DCCP and TFRC. New network systems and applications require the current transport protocols be modified or improved.Wireless Internet brings great challenges on the current network technologies and protocols. Because Internet protocols are designed for wired computer network originally, there must be some problems when implanting the traditional technologies and protocols to the nowadays wireless environments, such as performance, efficiency, stability and security .The wireless transport protocols is one of the key research issues.Wireless link has two main characteristics: instability and mobility. During the period of wireless communication, it is easily to encounter multi-path, interference, eclipse and handoff with the result of high bit error rate. Either the reliable data transport protocols or real-time multimedia stream transport protocols have the same basic idea that packet loss event in the connection is the only symbol that congestion happens and the decrease of sending rate or window is triggered by the packet loss detection. It is the major congestion control behavior in Internet. In wired links, bit error rate is so low that can be neglected and the major reason of packet loss is the congestion in Routers. The AIMD congestion control scheme has been proved to be effective in wired networks. But in wireless environment, the large amount of random packet losses due to wireless link error does not mean the deficiency of network resources. The traditional transport protocols such as TCP have no ability to distinguish the reason of packet loss so that they treat all the packet losses as the congestion signals and decrease the sending rate simply. The unnecessary rate decreasing can seriously deteriorate connecting performance.In this thesis, we firstly generalize the outline of the current wireless and mobile communication and networking, introducing some major wireless network systems i e. WLAN, Satellite network, WPAN and 3G cellular system which constitute of the architecture of Next Generation Wireless Internet (NGWI). The network structure, protocol details and applications of these different wireless systems are discussed in charter 2. We also conduct and analyze the four-state Markov state model which works as the end-to-end wireless path model in wireless Internet.Charter 3 and 4 respectively discuss the current transport protocols including reliable data and real-time multimedia used in wired Internet. In charter 2, we firstly introduce basic ideas and major functions of reliable data transport protocols. The most popular reliable data transport protocols in Internet are TCP series such as Tahoe, Reno, Sack , New Reno and Vegas etc. The core function in TCP----congestion control is discussed with its theories and algorithms. The basic four TCP congestion control algorithms including Slow Start, Congestion Avoidance, Fast Recovery and Fast Retransmit are studied and then we introduce two TCP throughput models: simple model and complex model in details. The TCP throughput models characterize the TCP behavior in Internet which is meaningful to evaluate and design other transport protocols.In charter 4 real-time multimedia transport protocols are discussed. RTP/RTCP protocol stack is architecture for transfer of real-time applications such as video, audio and analog data flows. It can provide many real-time services such as payload type, data sequence number, timestamp and transmission control etc. But RTP/RTCP is not a complete transport protocol because it simplifies its behavior by leaving some functions such as rate control and synchronization in other layers in order to improve its efficiency. So RTP/RTCP segments are usually carried by other transport protocols. The traditional TCP and UDP are not fit for transferring RTP/RTCP segments because of rate fluctuation of TCP and unfairness of UDP. To solve these problems, Stream control transport protocol (SCTP) and Date Congestion Control Protocol (DCCP) are proposed to replace TCP and UDP as the transport layer for RTP/RTCP. Furthermore, we discuss an important rate control scheme for real-time application ----TCP-friendly Rate control (TFRC) by analyzing its throughput model, packet structure and rate control process.The performance analysis and improvement of transport protocols in wireless networks are major tasks of this thesis. In charter 5, issues of wireless TCP are studied including the problems suffered from wireless environment and the comparison of various wireless TCP schemes. We focus our research on TCP-Jersey which makes use of available bandwidth estimation (ABE) and Congestion Warning (CW) mechanism. We modify TCP-Jersey and verify its good performance by NS-2 simulation in WLAN and wired-wireless hybrid environments. Charter 6 talks about the some rate control mechanisms of real-time multimedia stream in wireless networks. Firstly, we study an analytical rate control scheme ---ARC which is based on wireless TCP throughput model generalized in this charter. RCS is another wireless rate control scheme that consists of four states during a connection and use low priority packet Dummy to probe network and distinguish packet loss. In order to eliminate the unnecessary payload of Dummy packets, we modify RCS and embed it into DCCP. Simulation shows our proposed method has good performance in wireless network with high bit error rate and long communication delay. At the end of this charter, wireless TFRC schemes are discussed and a novel wireless TCP-friendly rate control scheme based on jitter ratio measurement is proposed. Extensive simulations verify that the TFRC-Jr has good throughput performance and reasonable TCP friendliness in wireless environments.In this these, based on deeply research of wireless network systems and transport protocols, we give a comprehensive generalization and analysis of reliable data and real-time stream transport protocols in the next generation of wireless Internet. New mechanisms such as TCP-Jersey+M, DCCP+RCS and TFRC-Jr are proposed and verified. At last, the future research goal and direction are proposed.