【作者】 张奭；

【导师】 刘增基；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2005， 博士

【摘要】 光突发交换(OBS:Optical Burst Switching)是一种介于光路交换和光分组交换之间的光交换技术。与光路交换相比,OBS采用的单向预留协议提高了波长带宽的利用率,可以更好的支持突发性很强的IP业务;与光分组交换相比,OBS为用户提供“光路”服务,避免使用复杂的光存储器件和光逻辑器件,更易于利用现有的技术实现。 本文研究OBS网络中的路由和波长分配(RWA)问题,主要工作包括: ● 波长转换范围受限条件下OBS网络中的RWA算法 在波长转换范围受限的OBS网络中,波长使用范围限制是造成突发阻塞的主要因素。针对OBS的分布式控制特点和单向预留协议所固有的盲目性,本文提出了一种波长转换范围受限条件下OBS网络的RWA算法,称之为基于指定光路的RWA(PL-RWA)。PL-RWA预先为每一个源宿结点对指定备选的光路集合,任意两个备选光路没有公共的波长链路。源宿结点对(s,d)的数据突发(DBs)尽可能的使用其备选光路集合中的光路,从而使DBs的传输尽可能的“各行其道”,以削弱OBS网络光路建立过程中的盲目性,减少波长使用范围限制造成的突发阻塞。当没有空闲的备选光路可用时,再实时按照常规RWA算法为DBs分配其它的光路。备选光路的选择和网络拓扑、可用波长数以及网络中突发业务的分布有关,本文分别用一个整数非线性规划和一个整数线性规划模型描述备选光路的选择问题,并给出了一种基于禁忌搜索的求解大规模问题的启发式算法。 ● 全范围波长转换条件下OBS网络中的路由算法 当OBS网络具备全范围波长转换能力时,光路的波长一致性限制被完全消除,路由算法成为影响OBS网络阻塞性能的主要因素。现有的路由算法通常以源宿结点对间的最短路径作为DBs的路由。这种路由算法存在两个问题:一、如果多个源宿结点对间的路由存在公用链路,在非对称的网络中,或网络业务量分布不均匀时,容易造成链路负载不均衡,加大突发阻塞概率。二、现有的路由算法很少考虑网络的失效保护问题,当发生网络故障时,无法及时调整DBs的路由,容易造成大量DBs丢弃。针对这两个问题,本文提出了两种分布式路由算法:基于蚂蚁系统的路由算法AS-R和基于概率的路由算法PR。 - 基于蚂蚁系统分布式路由算法AS-R:宿结点通过BCP-ACK消息指示一次成功的DB传输,BCP-ACKs按突发控制分组(BCP)相同的路径返更多还原

【Abstract】 Optical Burst Switching (OBS). which combines the benefits of wavelength routing and optical packet switching while taking into account the limitations of the current all-optical technology, seems to be a promising solution for all optical networks. Compared with wavelength routing, OBS can transmit bursty traffic efficiently by adopting one-way reservation protocol. On the other hand, OBS can be implemented easily on the basis of the current optical technology compared with optical packet switching.In this thesis, we focus on the Routing and Wavelength Assignment (RWA) of OBS. The main works and innovations are as follows.· RWA algorithm in OBS networks with limited wavelength conversionIn the networks with limited wavelength conversion, wavelength contention is the dominate reason that lead to burst blocking. The two notable features of RWA in OBS networks, the one-way resources reservation and distributed control scheme, make the establishment of the lightpath become rather randomness and uncertainty, especially the networks with limited range wavelength conversions. In this thesis, we present a RWA algorithm called pre-defined lightpath RWA (PL-RWA). In PL-RWA, initial routing of Data Bursts (DBs) is precisely designed to avoid wavelength contentions at intermediate nodes. At the network design stage, for each source-destination pair (s, d), a dedicated set of alternate lightpaths is predefined to guide the routing and wavelength assignment of the DBs of (s, d). The alternate lightpaths subject to the wavelength continuous constraint and are clash free. Source node s will pour the DBs destined for d into the alternate lightpaths predefined for (s,d) as many as possible. For the DBs that cannot be carried by the alternate lightpaths, the shortest path of (s,d) is selected as the route and wavelengths are assigned hop-by-hop in real time. Using alternate lightpaths, the randomness and uncertainty of one-way resources reservation under distributed control are diminished. The selection of alternate lightpaths is formulated as an integer non-linear programming and an integer linear programming respectively. A heuristic algorithm based on tabu search is given.? The routing algorithm in OBS networks with full range wavelength conversionIn the networks with full range wavelength conversion, the routing algorithm becomes the dominate reason that influence the network performance. The current RWA algorithms in OBS networks usually adopt the shortest path between the source-destination pairs as the routes and assign wavelengths hop-by-hop. There are two main problems exist in theses algorithms: (1) If there are common links among the shortest paths of different source-destination pairs, the one-way reservation protocol may cause congestion on these links while other links are underutilized, which may deteriorate the network performance, especially in an unsymmetrical network. (2) Few RWA algorithms take the fault recovery into consideration, which is important for the network to operate smoothly. We propose two routing algorithms called AS-R and PR respectively in this thesis.- An ant system based routing algorithm called AS-R is proposed. The destination nodes send BCP-ACK back for each successfully received Burst Control Packet (BCP). The BCP-ACKs are feed back along the same path as the one through which BCPs are forwarded. BCP-ACKs leave some "pheromone" along the path. The coming DBs will choose the output links with the probability proportioned to their pheromone intensity. The AS-R is robust for the network fault and can decrease burst blocking probability in an unsymmetrical network.- It was found that given the network topology and the traffic matrix, the probabilities that the DBs select different routes is almost unchangeable when the system reach to the stable state. We propose a probability-based routing algorithm in this thesis. Instead of using the shortest paths only, more than one alternate paths are pre-computed for a given source-destination pair (s,d). The DBs of (s,d) select their routes from the alternate paths with different probabilities which can be obtained from a non-linear programming (NLP). The objective of the NLP is to minimize the burst blocking probability of a given network. Numerical results shows that PR can decrease burst blocking probability more efficiently.? The deflection routingDeflection Routing is a important way for contention resolution in the space domain. A DB is sent to a different output link of the node and consequently on a different route toward its destination node. As a result, some part, of the traffic on the congested links are deflected to the underload links. Therefore, the traffic load on various links are balanced. We discuss two different deflection schemes called Forward Deflection Routing and Drop and Backward Deflection Routing and Drop respectively. Meanwhile, a Hop-related Offset Time (HOT) algorithm is proposed to modify the initial offset time of the DBs and weaken the path length priority effect in JET.? Design of the OBS simulation environmentIn view of the complicated behavior of the OBS networks, simulation plays a important role in the process of protocol design, test and evaluation. We develop a simulation platform of OBS network based on NS-2 called OBSns.更多还原