Components Of External Path Computing - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide
696
Currently, only online and real-time constraint-based routing path computation is provided
in an MPLS RSVP-TE network. Each router performs constraint-based routing calculations
independent of the other routers in the network. These calculations are based on currently
available topology information—information that is usually recent, but not completely
accurate. LSP placements are locally optimized, based on current network status. The
MPLS RSVP-TE tunnels are set up using the CLI. An operator configures the TE LSP,
which is then signaled by the ingress router.
In addition to the existing traffic engineering capabilities, the MPLS RSVP-TE functionality
is extended to include an external path computing entity, called the Path Computation
Element (PCE). The PCE computes the path for the TE LSPs of ingress routers that have
been configured for external control. The ingress router that connects to a PCE is called
a Path Computation Client (PCC). The PCC is configured with the Path Computation
Client Protocol (PCEP) to facilitate external path computing by a PCE.
For more information, see
To enable external path computing for a PCC's TE LSPs, include the
statement at the
pccd [edit mpls]

Components of External Path Computing

The components that make up an external path computing system are:
Path Computation Element on page 696
Path Computation Client on page 697
Path Computation Element Protocol on page 698
Path Computation Element
A Path Computation Element (PCE) can be any entity (component, application, or
network node) that is capable of computing a network path or route based on a network
graph and applying computational constraints. However, a PCE can compute the path
for only those TE LSPs of a PCC that have been configured for external control.
A PCE can either be stateful or stateless.
Stateful PCE—A stateful PCE maintains strict synchronization between the PCE and
network states (in terms of topology and resource information), along with the set of
computed paths and reserved resources in use in the network. In other words, a stateful
PCE utilizes information from the traffic engineering database as well as information
about existing paths (for example, TE LSPs) in the network when processing new
requests from the PCC.
A stateful PCE is of two types:
Passive stateful PCE—Maintains synchronization with the PCC and learns the PCC
LSP states to better optimize path calculations, but does not have control over them.
Active stateful PCE—Actively modifies the PCC LSPs, in addition to learning about
the PCC LSP states.
"Components of External Path Computing" on page
and
[edit mpls lsp lsp-name]
696.
lsp-external-controller
hierarchy levels.
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