Cr-Ldp; Rsvp-Te - 3Com MSR 50 Series Configuration Manual

For a new path to preempt an existing path, the setup priority of the new path
must be greater than the holding priority of the existing path. To initiate a
preemption, the RESV message of RSVP-TE is sent.
To avoid flapping caused by improper preemptions between CR-LSPs, the setup
priority of a CR-LSP should not be set higher than its holding priority.
Route pinning
Route pinning prevents an established CR-LSP from changing upon route changes.
If a network does not run IGP TE extension, the network administrator will be
unable to identify from which part of the network the required bandwidth should
be obtained when setting up a CR-LSP. In this case, loose explicit route (ER-hop)
with required resources is used. The CR-LSP thus established however, may change
when the route changes, for example, when a better next hop becomes available.
If this is undesirable, the network administrator can set up the CR-LSP using route
underpinning to make it a permanent path.
Administrative group and affinity attribute
The affinity attribute of an MPLS TE tunnel identifies the properties of the links
that the tunnel can use. Together with the link administrative group, it decides
which links the MPLS TE tunnel can use.
Reoptimization
Traffic engineering is a process of allocating/reallocating network resources. You
may configure it to meet desired QoS.
Normally, service providers use some mechanism to optimize CR-LSPs for best use
of network resources. They can do this manually but CR-LSP measurement and
tuning are required. Alternatively, they can use MPLS TE where CR-LSPs are
dynamically optimized.
Dynamic CR-LSP optimization involves periodic calculation of paths that traffic
trunks should traverse. If a better route is found for an existing CR-LSP, a new
CR-LSP will be established to replace the old one, and services will be switched to
the new CR-LSP.

CR-LDP

Constraint-based routed label distribution protocol (CR-LDP) is an extension to
LDP. It is used in MPLS TE to create an explicit path with resource reservation
between the ingress node and the egress node.
When initiating an LSP at the ingress, CR-LDP appends some constraints in the
label request message.

RSVP-TE

This section covers these topics:
"Overview" on page 1350
■
"Basic concepts of RSVP-TE" on page 1350
■
"Make-before-break" on page 1351
■
"RSVP-TE messages" on page 1351
■
"Setting up an LSP tunnel" on page 1352
■
MPLS TE Overview 1349