提供大量頻寬的次世代光網路(Next-generation optical transport networks)已經成為未來骨幹網路的趨勢。ITU-T制定了光網路的基本架構(ASON)，而IETF也針對這些架構提出了一些利用GMPLS來控制以及管理光網路。基於光網路的特性，每個波長(Wavelength)可以攜帶大量的流量(Traffic)，波長越多，頻寬越大。但是相對的，在處理選徑以及波長選擇(RWA: Routing and wavelength assignment)上的複雜度，也隨著網路規模的增加而越漸複雜。論文中使用ASON階層式的網路來做管理，可以增加網路的scalability。 本論文中針對建構階層式網路提出了一個演算法，依照每個光交換機的所在位置，將實體的網路切割成為數個區域(Domain)形成邏輯節點，提供给上層的邏輯拓樸使用。每個邏輯節點中具有將拓樸資訊彙整的Intra- Domain Aggregation scheme，以及當光交換機提出光通道(Lightpath)要求時在Intra- Domain及Inter- Domain之間建立光通道的方式。並且利用分層的概念，可以降低處理Routing and Wavelength Assignment所花費的時間以及運算。 Next-generation optical transport network can support lots of bandwidth and it is regarded as a convincible solution of future backbone network. In order to support this technique, ITU-T has recommended the Automatically Switched Optical Networks (ASON) specifications and IETF has defined the Generalized MPLS (GMPLS) suite of protocols to achieve this goal. Based on the characterization of the optical network, every wavelength can carry huge traffic and the bandwidth can dramatically increase by using multiple wavelengths in the fiber.. And the establishment of ligthpaths shall consider not only the routing strategy but also the allocation of wavelength. However, the time complexity of RWA (Routing and wavelength assignment) algorithm will always be the most critical issue when the network augments.. This paper focuses on providing ASON with hierarchical routing in order to ensure the scalability for large worldwide networks. This paper proposes the abstract topology construct scheme by using the hierarchical optical network concept and the the degree of node and its position in the network. The scheme can divide the flat network into many domains, each domain is treated as a abstract node in the logical topology. The Intra- Domain Aggregation scheme is proposed to aggregate the information of domain and provide it to the “Inter-Domain Routing Scheme” for routing. Simulation results show that the benefits of our scheme can reduce connection blocking rate and the resource utilization.
