Multi layer path computation

When a end-to-end path computation crosses diverse layers it is called inter-layer path computation. The RFC 4206 defines how a higher-layer LSP that has explicit route object traversing lower-layer LSPs should be signaled. However, it might happen that a higher-layer Label Switched Router does not have topology visibility of the lower layer. A higher-layer / Lower-layer situation can be exemplified by a IP packet-based GMPLS over a GMPLS Optical network (could be a WDM Network).

This problem can be dodge by the implementation of either a single PCE model or a multiple PCE model (refer to the figure at the bottom of the post). In the single PCE model, the PCE unity has visibility in all the layers, and performs solely the end-to-end path computation. In the multiple PCE model, each PCE object has visibility restricted to its own layer, and therefore its Traffic Engineering Database is reduced. In this model PCEs from the different layers must communicate between each other and collaborate in the end-to-end path computation.

Picture extracted from Oki et al., 2008

Oki, E.; Inoue, I. & Shiomoto, K. (2008), 'Path computation element (PCE)-based traffic engineering in MPLS and GMPLS networks''Sarnoff Symposium, 2007 IEEE', IEEE, 1--5.