This paper overviews network design issues of the photonic transport network (PTN), which employs wavelength division multiplexing (WDM) and wavelength routing. The design issues are considered on the level of newly created high-speed transmission access paths, i.e., optical paths (OPs). These include the routing and wavelength assignment (RWA) problems involved in making the best use of network resources such as wavelengths and fibers. With this objective, design issues for ring and meshed type PTN are addressed by presenting the results of case studies in which existing heuristic RWA algorithms were employed. By utilizing the design tools, the possible network scale is then estimated, while considering state-of-the-art hardware realization technologies. Further consideration is given assuming an environment where PTN serves as a high-speed IP-backbone. An extensive case study shows the cost-effectiveness of IP-over-PTN over other scenarios such as IP-over-(point-to-point) WDM.