This paper discusses quality-of-service (QoS) multicast in wavelength-divis
ion multiplexing (WDM) networks. Given a set of QoS multicast requests, we
are to find a set of cost suboptimal QoS routing trees and assign wavelengt
hs to them. The objective is to minimize the number of wavelengths in the s
ystem. This is a challenging issue. It involves not only optimal QoS multic
ast routing, but also the optimal wavelength assignment. Existing methods c
onsider channel setup in WDM networks in two separate steps: routing and wa
velength assignment, which has limited power in minimizing the number of wa
velengths. In this paper, we propose a new optimization method, which integ
rates routing and wavelength assignment in optimization of wavelengths. Two
optimization algorithms are also proposed in minimizing the number of wave
lengths. One algorithm minimizes the number of wavelengths through reducing
the maximal link load in the system; while the other does it by trying to
free out the least used wavelengths. Simulation results demonstrate that th
e proposed algorithms can produce suboptimal QoS routing trees and substant
ially save the number of wavelengths.