Study On The Key Techniques For The Core Nodes In The Optical Burst Switched Network

The current optical network is basically an optical transmitting and electrical switching system.It is evolving into an all-optical transporting system with optical transmitting and optical switching capability while the requirements of bandwidth explosively grow and the transmission technologies keep making breakthroughs. Among several proposed optical switching techniques, the Optical Burst Switching (OBS) attracts more attention for its supporting packet-based traffics and technological feasibility. In OBS networks, the control plane, working in the electrical domain, is separated from the optical transport plane in wavelength used, and the end-to-end all-optical data transport is realized by using such techniques as traffic convergence, data burst assembly, one-way resource reservation etc.In the research of OBS,how to further reduce the data loss caused by random burst conflictions,and how to combine tightly the research of OBS with the development and evolution of current optical networks so as to apply it as soon as possible, are two important topics.This thesis makes some major contributions in both aspects, as follows.The theoretical and approximate analysis of OBS switching architectures with shared Wavelength Converters (WCs) is proposed, and the performances of various architectures are compared. An effective way to resolve the burst confliction in OBS nodes is using WCs.Since WCs are expensive, switching architectures capable of sharing them are designed to reduce the cost. According to the characteristics and working process of the switches with shared WCs, we propose an accurate analytical method to the Share-per-Link (SPL) architecture.And based on that, approximate evaluation models are established for both SPL and Share-per-Node (SPN) architecture. By using some traits in common between the two models, the feedback parameters in the approximate models can be obtained from the results of accurate analysis of SPL, through which the approximate loss probability of SPN can be estimated.With analytical and approximate methods,the performance of switching nodes and the effect of various configurations of WCs upon the switching performance are investigated.We propose a new analytical method to the asynchronous switching node with limited range wavelength converters.Using limited-range wavelength converters in the switching node instead of full range ones is another effective approach to reduce the cost of nodes.But the introduction of limited-range converters makes the loss probabilities in asynchronous switching mode too complicate to be analyzed. In a published work an analytical model is built on single wavelength conversion set, reducing the dimension of the problem but introducing too much error due to its assumptions.We propose a new method that uses the number of occupied wavelengths in one output port as system state parameter so as to build an arrival-discouraged random queuing model.To find the averaged arrival rate in each system state,a theorem on the averaged number of runs of certain length of balls randomly placed in a circle of boxes is proved. And through which the equilibrium equations and the burst loss probability of the queuing system are able to be resolved with available conclusions. Both simulation and analysis show the method is advantageous to the previous one.We propose four scheduling methods of burst splitting/discarding in switching nodes with shared wavelength converters and analyze their performances.As a data burst in OBS consists of a large number of upper layer packets, in the resolution of burst contention, a method of discarding only the collided part of contending bursts can be adopted to reduce the loss of user data, such as in Optical Composite Burst Switching (OCBS)and Burst Segmentation (BS).It is shown that such methods can reduce the data loss significantly without changing any hardware components in the node. Currently most of the researches on OCBS/BS assume that the switching node is fully wavelength convertible but such assumptions are not so realistic.Therefore, we suggest four scheduling algorithms of splitting/discarding contending burst in the switching nodes with shared wavelength converters.Through simulations the loss performances of them and the traditional scheduling method based on whole burst are compared, and the best one in overall performances is point out.We present an innovative design of optical burst ring. The presented scheme uses an effective resilient off-time control mechanism (ROTC) to keep the lasting correspondence between the burst control label (BCL) in the control channel and the data burst slot (DBS) in the data channels,and thus it is named Virtual Asynchronous Optical Burst Ring (VS-OBR).The major advantages of VS-OBR are its, supporting the space reuse of fiber links, fast and flexible bandwidth accessing, permitting preemptive priority and requiring neither FDLs in each node nor strict clock synchronization through the network.We describe in detail the node architecture,BCL and DBS formats and the working process of VS-OBR, analyze several key technical problems and the throughputs under saturated loads, and study end-to-end delay and effective throughput performances with simulation methods.