Subject: [Pce] Document Action: 'The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS and GMPLS' to Informational RFC (draft-ietf-pce-hierarchy-fwk-05.txt)

From: The IESG <[email-masked]>
Date: Fri, 05 Oct 2012 11:04:31 -0700

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