Juniper ACX1000 Configuration Manual page 755

Copyright © 2017, Juniper Networks, Inc.
NOTE: In a redundant configuration with main and backup active stateful
PCEs, the backup active stateful PCE cannot modify the attributes of
delegated LSPs until it becomes the main PCE at the time of a failover.
There is no preempting of PCEs in the case of a switchover. The main
PCE is backed by a backup PCE, and when the main PCE goes down, the
backup PCE assumes the role of the main PCE and remains the main
PCE even after the PCE that was previously the main PCE is operational
again.
A stateful PCE provides the following functions:
Offers offline LSP path computation.
Triggers LSP re-route when there is a need to re-optimize the network.
Changes LSP bandwidth when there is an increase in bandwidth demand from an
application.
Modifies other LSP attributes on the router, such as ERO, setup priority, and hold
priority.
A PCE has a global view of the bandwidth demand in the network and maintains a
traffic-engineered database to perform path computations. It performs statistics
collection from all the routers in the MPLS domain using SNMP and NETCONF. This
provides a mechanism for offline control of the PCC's TE LSPs. Although an offline
LSP path computation system can be embedded in a network controller, the PCE acts
like a full-fledged network controller that provides control over the PCC's TE LSPs, in
addition to computing paths.
Although a stateful PCE allows for optimal path computation and increased path
computation success, it requires reliable state synchronization mechanisms, with
potentially significant control plane overhead and the maintenance of a large amount
of data in terms of states, as in the case of a full mesh of TE LSPs.
Stateless PCE—A stateless PCE does not remember any computed path, and each
set of requests is processed independently of each other (RFC 5440).
Path Computation Client
A Path Computation Client (PCC) is any client application requesting a path computation
to be performed by a PCE.
A PCC can connect to a maximum of 10 PCEs at one time. The PCC to PCE connection
can be a configured static route or a TCP connection that establishes reachability. The
PCC assigns each connected PCE a priority number. It sends a message to all the
connected PCEs with information about its current LSPs, in a process called LSP state
synchronization. For the TE LSPs that have external control enabled, the PCC delegates
those LSPs to the main PCE. The PCC elects, as the main PCE, a PCE with the lowest
priority number, or the PCE that it connects to first in the absence of a priority number.
Chapter 23: Configuring Path Computation Element Protocol (PCEP)
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