Research On Some Key Technologies Of Optical Resilient Packet Ring

Resilient Packet Ring (RPR) is a network based on the protocol of packet transport. As a popular solution to Metropolitan Area Network (MAN), In an RPR network, frequent transform of packets from electrical to optical or contrariwise not only complicates the system, but also affects the system performance. Therefore, using optical domain processing technique at nodes has won more and more attention recently. With all-optical switching technology introduced, ORPR replaces electrical transfer buffer with optical transfer buffer. ORPR simplifies the structure of a node, decreases its processing load, and increases the network capacity by avoiding the unnecessary O/E/O conversion of the transfer packets.This paper proposes an ORPR network node structure. Several key problems are studied deeply, e.g., variation after introduction of optical buffer, optical packet assembly, fairness protocol of MAC, and time delay and performance for ORPR network. Multiple achievements are obtained.In summary, the main contributions and creations of this work lie in aspects as follows:1. Based on analyses of RPR and full optical packet switching network, an ORPR node structure is proposed, and hierarchical structure and protocol for ORPR are defined. The advantages of ORPR structure over ERPR are clarified. The differences in fairness algorithms and network scheduling for ORPR and ERPR are discussed.2 Study the effect of buffer capacity and ring length of fiber ring buffer on packet loss probability (PLP) in communication when using fiber ring as buffers. Analytical results are presented. The increased PLP is mainly caused by the additional operation resulted from the introduction of fiber ring. A concept of buffers precision is introduced in this paper. The relationship between the PLP and buffers precision, buffer capacity and additional operation is analyzed in detail. PLP is determined by not only buffer capacity,but also buffer precision. An optical point of buffer precision exists for certain server utilization.3 Analyzed optical packets assembly algorithm when traffic shaped in an ORPR network and proposed a new algorithm fit for ORPR network by controlling the time in transmission. The algorithm is based on a hybrid threshold assembly algorithm. It adds a parameter to control the interval between optical packets transmitted so that the traffic in each time unit is smoothed to be less burst. It also ensures the QoS performances of the network and fit for the ORPR network with limited optical buffer. The average assembly time-delay of optical packets is analyzed in detail. The average assembly time-delay is influenced much by the time threshold in case of light traffic load while the length threshold influence more with the traffic load increasing. The heavier the traffic load, the less the average assembly time-delay. By adjusting the interval of packet transmission in new algorithm, we obtain about the same distribution of assembly time-delay under different traffic load. The stable pack-ets average assembly time-delay is very important to QoS and fairness of ORPR. Choosing the good timing for packet transmission is one of the keys to ensure the QoS and fairness of the ORPR.4 End to end delay of packet in ORPR node was analyzed. The computing equation for end to end average delay of packet with different service priority was proposed, while fiber ring acting as transfer buffer at ORPR node. The relationship between delay and traffic, fiber ring unit length is analyzed via the equation. Our simulation results demonstrate that the new algorithm gives a relatively stable packets average assembly time-delay and that is satisfied in most situations in the ORPR network5 Fairness principle of ORPR network is discussed, and a fairness realization algorithm and method for ORPR network is proposed. The algorithm used a rate control frame circling in the ring, distributing rate information of each node to whole ORPR network, bandwidth resource is allocated fairly for each data stream of shared link, ensure fairness and high efficiency of link utilization in whole ORPR network. Adjusting rate not based on traditional buffer usage is the unique characteristic of the algorithm, the proactive mechanism can ensure each data flow can be controlled before sending, the congestion will not happen while passing through nodes and links, so the algorithm is suitable for ORPR network lack of buffer.