Multi layer path computation with PCE

In a distribute multi-layer path computation a Label Switched Router (LSR) in a higher may not have information on the topology or network state of a lower layer and hence may not be able to compute an end-to-end path.
In a centralized multi-layer path computation there are two alternatives for a successful end-to-end path computation:
1- Single PCE path computation: the PCE has topology and network state information about multiple layers in a network and can directly compute a required end-to-end path.
2- Multiple PCE path computation:
 a- with inter PCE communication: PCEs collaborate and each PCE is responsible for the path computation on its own layer.
 b- without inter PCE communication: each PCE computes PCE for its own layer after the request of its layer ingress LSR.

Takeda, T.; Oki, E.; Marzin, A.; Farrel, A. & Roux, J. (2009), 'Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic Engineering', Framework .