DWDM 망에서 파장 변환 기능 및 QoS 기반의 제한적 플러딩 RWA 알고리즘에 관한 연구

Abstract

In the next-generation Internet backbone network, DWDM(Dense-Wavelength Division Multiplexing) technology has appeared as an alternative method to solving problems with lack of bandwidth on the Internet based on the existing TDM(Time Division Multiplexing). In this DWDM Network, to satisfy the efficient use of resources and necessary requirements of each user, it is inevitable to consider the matter of RWA(Routing and Wavelength Assignment) together with the wavelength conversion function, in the case of setting up a connection. In DWDM networks, the wavelength-continuity constraint can be eliminated and resource utilization can be improved if a WC(Wavelength Converter) with full wavelength conversion capability exists at each node. However, although full wavelength conversion is desirable, it is difficult to implement in practice due to technological limitations and its high cost. Therefore, this dissertation suggests an efficient technique for the limited wavelength conversion function. In a wavelength-routed DWDM network, the network edge systems communicate with one another via all-optical WDM channels, which are referred to as lightpaths. Given a set of connection requests, the problem of setting up lightpaths by routing and assigning a wavelength for each connection, so that no two lightpaths on a given link share the same wavelength, is called the routing and wavelength assignment problem. The RWA problem is very important and plays a key role in improving the global efficiency for capacity utilization in DWDM networks providing multi-gigabit rates per wavelength. However, it is a combinational problem known to be NP-complete because RWA problems are tightly linked together. Since it was more difficult to work out RWA as a coupled problem, this problem has been approximately divided into two sub-problems: routing and wavelength assignment. In previous studies, the routing scheme has been recognized as a more significant factor in the performance of the solution of the RWA problem than the wavelength assignment scheme. This dissertation proposes a new QoS routing algorithm based on a flooding method, called a bounded flooding routing(BFR) algorithm which can meet multi-constraint QoS requirements. Primarily, the BFR algorithm tries to reduce network overhead by accomplishing bounded-flooding to meet QoS requirements, and to improve blocking probability and wavelength utilization. Also, in an effort to improve routing performance, we introduce a new concept called ripple count, which can classify incoming messages into three types and determine whether the message is necessary or not through simple comparison without link-state information and computational processes. Moreover, we also make an effort to improve blocking probability through two different methods(i.e. first come first serve path selection and least-congested path selection) at a destination node. Also, with the BFR algorithm, we adopt first-fit as a wavelength assignment algorithm, which requires no global information and has a low computational cost. The simulation results show that the BFR algorithm is superior to other predominant routing algorithms(both original flooding method and source-directed methods) in terms of blocking probability, network overhead and resource utilization.