The IESG has approved the following document: - 'The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS and GMPLS' (draft-ietf-pce-hierarchy-fwk-05.txt) as Informational RFC This document is the product of the Path Computation Element Working Group. The IESG contact persons are Stewart Bryant and Adrian Farrel. A URL of this Internet Draft is: http://datatracker.ietf.org/doc/draft-ietf-pce-hierarchy-fwk/ Technical Summary Computing optimum routes for Label Switched Paths (LSPs) across multiple domains in MPLS Traffic Engineering (MPLS-TE) and GMPLS networks presents a problem because no single point of path computation is aware of all of the links and resources in each domain. A solution may be achieved using the Path Computation Element (PCE) architecture. Where the sequence of domains is known a priori, various techniques can be employed to derive an optimum path. If the domains are simply-connected, or if the preferred points of interconnection are also known, the Per-Domain Path Computation technique can be used. Where there are multiple connections between domains and there is no preference for the choice of points of interconnection, the Backward Recursive Path Computation Procedure (BRPC) can be used to derive an optimal path. This document examines techniques to establish the optimum path when the sequence of domains is not known in advance. The document shows how the PCE architecture can be extended to allow the optimum sequence of domains to be selected, and the optimum end-to-end path to be derived through the use of a hierarchical relationship between domains. Working Group Summary There was nothing unusual to note in the progression of this document through the working group. Document Quality This is a well written document. Personnel Julien Meuric is the Document Shepherd. Stewart Bryant is the Responsible Area Director. RFC Editor Note Section 3 Para 2, s/TED/TED (Traffic Engineering Database)/ ==== Section 3 OLD Note that in the case that the domains are IGP areas, there is no link between the domains (the ABRs have a presence in both neighboring areas). The parent domain may choose to represent this in its TED as a virtual link that is unconstrained and has zero cost, but this is entirely an implementation issue. NEW Note that in the case that the domains are IGP areas, there is no link between the domains (the ABRs have a presence in both neighboring areas). The parent domain may choose to represent this in its traffic Engineering Database (TED) as a virtual link that is unconstrained and has zero cost, but this is entirely an implementation issue. END --- Section 4.1 OLD Deriving the optimal end-to-end domain path sequence is dependent on the policy applied during domain path computation. An Objective Function (OF) [RFC5541], or set of OFs, may be applied to define the policy being applied to the domain path computation. The OF specifies the desired outcome of the computation. It does not describe the algorithm to use. When computing end-to-end inter- domain paths, required OFs may include (see Section 1.3.1): o Minimum cost path o Minimum load path o Maximum residual bandwidth path o Minimize aggregate bandwidth consumption o Minimize or cap the number of transit domains o Disallow domain re-entry The objective function may be requested by the PCC, the ingress domain PCE (according to local policy), or applied by the parent PCE according to inter-domain policy. More than one OF (or a composite OF) may be chosen to apply to a single computation provided they are not contradictory. Composite OFs may include weightings and preferences for the fulfilment of pieces of the desired outcome. NEW The definition of "optimal" in the context of deriving an optimal end-to-end path is dependent on the choices that are made during the path selection. An Objective Function (OF) [RFC5541], or set of OFs, specify the intentions of the path computation and so define the "optimality" in the context of that computation. An OF specifies the desired outcome of a computation: it does not describe or demand the algorithm to use, and an implementation may apply any algorithm or set of algorithms to achieve the result indicated by the OF. OFs can be included in PCEP computation requests to satisfy the policies encoded or configured at the PCC, and a PCE may be subject to policy in determining whether it meets the OFs included in the computation request, or applies its own OFs. In inter-domain path computation, the selection of a domain sequence, the computation of each (per-domain) path fragment, and the determination of the end-to-end path may each be subject to different OFs and different policy. When computing end-to-end paths, OFs may include (see Section 1.3.1): o Minimum cost path o Minimum load path o Maximum residual bandwidth path o Minimize aggregate bandwidth consumption o Minimize or cap the number of transit domains o Disallow domain re-entry The objective function may be requested by the PCC, the ingress domain PCE (according to local policy), or applied by the parent PCE according to inter-domain policy. More than one OF (or a composite OF) may be chosen to apply to a single computation provided they are not contradictory. Composite OFs may include weightings and preferences for the fulfilment of pieces of the desired outcome. END
