In a WDM transport network

internal dependence of lightpaths could lead to the critical status that the failure of a physical fiber leaves the virtual topology unconnected.This may make the restoration of service by the higher level networks using the WDM network (such as SDH

ATM or IP) impossible.It is necessary to avoid the above cases while embedding virtual topology into physical topology.Existent Disjoint Alternate Path (DAP) algorithm always assumes that all network nodes have full-range wavelength conversion capability.A new heuristic algorithm

called Virtual Topology Mapping for Design Protection Based on Layered Graph (LG

-VTMDP)

used in design protection for WDM optical networks is proposed in this paper.The algorithm considers two problems of routing and wav

elength assignment simultaneously.Load balancing and capacity constraints of physical links are also considered.The LG

-

VTMDP algorithm is shown to perform better than the combination of the DAP algorithm and existent wavelength assignment algorithms.Based on the result of the LG

-

VTMDP algorithm

an efficient Wavelength Converter Placement (WCP) algorithm is presented subsequently.