Considering survivability in fiber-optic transmission networks using B-DCS(Broadband Digital Crossconnect System), a network design problem consists of WCAP(Working Channel Assignment Problem) and SCAP(Spare Channel Assignment Problem). WCAP has not been studied intensively as a part of a network design problem to minimize total network cost while SCAP has been studied in the several papers as an independent problem. In this study, we developed a WCAP algorithm which is to minimize the total number of spare channels and working channels. After problem description, an IP(Integer Programming) model is formulated and several heuristic algorithms are presented. Finally, the result of a case study is described.