Path Computation Flooding

In a multi-domain network when a end-to-end path computation relies on a fixed, previously known domain sequence the resulting end-to-end path is considered to suboptimal in terms of resulting blocking probability (Hernández-Sola et al, 2010). To improve the optimality of the resulting path, the domain sequence should ideally be calculated on demand by one or more PCEs present in the network. However to achieve this optimality the number of overhead control messages is increased and therefore the burden of processing in the PCEs jeopardizes the scalability of the whole system, since the larger the multi-domain network the higher is the necessity of processing of control messages (Perelló et al., 2010). The control messages refer to both the constant update on link state (via OSPFs link sate advertisement) and the messages exchanged between different domains PCEs. 

Based on the BRPC, the Path Computation Flooding (PCF) is a different approach where a domain sequence is not previously stipluated. In this architecture, the destination domain PCE upon receipt of a PCReq from the source domain PCE calculates an egress VSPT and sends this as a message to all the PCE in adjacent domains and so on so forth till the PCE in the source domain receives a VSPT from all of his adjacent domain PCEs and selects the final optimum path (King & Farrel, 2009). The PCF generates too many control overhead messages and therefore presents serious scalability issues. 

Hernández-Sola, G.; Perelló, J.; Spadaro, S.; Moreno, A.; Agraz, F.; Comellas, J. & Junyent, G. (2010), Analysis of traffic engineering information dissemination strategies in PCE-based multi-domain optical networks, in 'Transparent Optical Networks (ICTON), 2010 12th International Conference on', pp. 1—4. 

King, D. and Farrel, A. “The Application of the PCE Architecture to the Determination of a Sequence of Domains in MPLS &GMPLS,” IETF draft draft-king-pce-hierarchy-fwk-03.txt, Dec. 2009. http://tools.ietf.org/html/draft-king-pce-hierarchy-fwk-00

Perelló, J.; Hernández-Sola, G.; Agraz, F.; Spadaro, S. & Comellas, J. (2010), 'Scalable Path Computation Flooding Approach for PCE-Based Multi-domain Networks', ETRI journal 32(4).