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
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)/
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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
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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