A cluster-based WDM network is proposed in this paper

where each user is equipped with afix tuned receiver and a limited tunalbe transmitter.The network achieves constant maximum hop of 2. It adoptsa systematic channel assignment algorithm （ CAA） to minimize the tuning range of each transmitter meanwhileminimizing the average hop. Analysis and mumerical results show that the network obtains equivalent single hopprobability among clusters under the uniform traffic . Furthermore

its basic performance such as average hop andmaximum throughput

is almost only related with wavelength number

having little to do with the user number.