In this paper

we propose an optimal cost model for IP/MPLS-over-EON.Based on the model

two path segmentation routing schemes are presented:the adaptive and the heuristic.The construction cost of the IP/MPLS-over-EON based on these two schemes are investigated.The adaptive scheme enumerates every intermediate node of a path one by one to choose the path-segment point

in which an IP router will be placed and the path will have the minimum cost.The heuristic scheme implements path segmentation by setting a specific distance.When the distance is reached

a router will be placed for path segmentation.Numerical results demonstrate that when compared with the scheme of no path segmentation

the routing scheme of path segmentation can lower the total network cost effectively for medium and high load traffic profiles.It is because that for medium and high load traffic profiles

more traffic need to and can be groomed in intermediate nodes with IP routers being placed in intermediate nodes.