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MPLS and RSVP-TE
3.12.2.2
In the PCC-initiated and PCE-computed/controlled LSP mode of operation, the
ingress LER uses PCEP to communicate with a PCE-based external TE controller
(also referred to as the PCE). The router instantiates a PCEP session to the PCE.
The router is referred to as the PCE client (PCC).
When the user enables the pce-computation option for one or more SR-TE LSPs,
the PCE performs path computations at the request of the PCC, which is referred to
as passive stateful mode. If the user enables the pce-control option for an LSP, the
PCE can also perform both path computation and periodic reoptimization of the LSP
path without an explicit request from the PCC. This is referred to as active stateful
mode.
For the PCC to communicate with a PCE about the management of the path of an
SR-TE LSP, the router implements the extensions to PCEP in support of segment
routing (see
PCE, which is part of the network services platform (NSP).
The following steps describe configuring a PCC-initiated SR-TE LSP when passive
or active control is given to the PCE.
98
PCC-initiated and PCE-computed/controlled LSP
PCEP
for more information).This feature works with the Nokia stateful
1. The SR-TE LSP configuration is created on the PE router using the CLI or
NSP NFM-P.
The configuration dictates which PCE stateful mode is desired: active (pce-
control option enabled) or passive (pce-computation enabled and pce-
control disabled).
2. The PCC assigns a unique PLSP-ID to the LSP. The PLSP-ID uniquely identifies
the LSP on a PCEP session and must remain constant during its lifetime. The
PCC on the router tracks the association of {PLSP-ID, SRP-ID} to {tunnel-ID,
path-ID} and uses the latter to communicate with MPLS about a specific path of
the LSP.
3. The PE router does not validate the entered path. While the PCC can include
the IRO objects for any loose or strict hop in the configured LSP path in the path
computation request (PCReq) message to the PCE, the PCE ignores the IRO
objects and computes the path with the other constraints.
4. The PE router sends a PCReq message to the PCE to request a path for the
LSP and includes the LSP parameters in the METRIC object, the LSPA object,
and the BANDWIDTH object. It also includes the LSP object with the assigned
PLSP-ID. At this point, the PCC does not delegate control of the LSP to the PCE.
5. The PCE computes a new path, reserves the bandwidth, and returns the path in
a path computation reply (PCRep) message with the computed ERO in the ERO
object. It also includes the LSP object with the unique PLSP-ID, the METRIC
object with the computed metric value if any, and the BANDWIDTH object.
Use subject to Terms available at: www.nokia.com
© 2022 Nokia.
MPLS Guide
3HE 18686 AAAB TQZZA
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