在現今網際網路蓬勃發展之下,頻寬需求量也隨之遽增,如視訊會議,各類多媒體服務等等,都需要高速即時且高容量的網路傳輸服務來達到QoS。光纖網路DWDM(Dense Wavelength Division Multiplex)系統能夠提供高速及高容量的網路傳輸服務,加上多點傳播(multicast)機制,便能有效率的利用網路頻寬及其他資源,進行視訊會議,視訊廣播等一對多傳輸服務。而在光網路下的多點傳播,目前最被廣泛使用的樹狀路徑拓撲架構,稱為Light-Tree,能將網路封包平均傳輸節段距離最小化,同時將網路收發設備使用總數最少化,進行一對多(point to multipoint)的網路傳輸工作。而如視訊會議此類需要長時間多對多(many to many)傳輸的網路服務,如利用Light-Tree拓撲架構,將會在各個會議成員需要進行多點傳播時建立各自的樹狀路徑,如果使用預留路徑配置的方式,可以省去每次需要傳輸時尋找路徑的時間,亦可減少網路傳輸阻塞率。但是以樹狀路徑當作預留路徑,並不是最理想的拓撲架構,因為收發裝置以及波長頻道被預留,使得其他會議無法同時使用,若會議數量增加時,較晚舉行的會議將可能因為資源不足無法舉行。本文提出一種混合式繞徑與波長分配(Hybrid Routing and Wavelength Assignment, HRWA)演算法,以環狀路徑為主,並當光網路資源不足時加入樹狀結構路徑,在網狀拓撲(Mesh Topology)的光網路下,盡可能將所有會議成員以一個環狀路徑連接,並透過路徑及波長頻道預留的方式,進行多對多的多點傳播。其結果可減少同一時間在網路上所佔用的收發裝置以及波長頻道,以增加同時段可進行多對多多點傳播數量,減少連線要求阻礙機率(call blocking probability),進而提升網路各資源的使用率。
The DWDM (Dense Wavelength Division Multiplex) technique can provide the high speed and high capacity transmission, and the multicast schemes can be efficiently applied in DWDM technique to support QoS guarantees and time-consuming many-to-many transmission services, such as video conference and video broadcasting. We propose a HRWA (Hybrid Routing and Wavelength Assignment) algorithm in optical mesh network with light-tree-based virtual topology. First, the HRWA try to connect all multicast group members with ring path as possible, and then join tree paths are considered when there is no such ring path available. Thereafter, the HRWA will proceed to many-to-many multicast transmission by reserving links and channels, and wavelengths will be assigned by LCC (Least Converter Counts) algorithm. The objective of the proposed HRWA algorithm is to improve system resource utilization, such as increasing the number of many-to-many multicast sessions with less reserved channels and lowering call blocking probability to support more user capacity.