57
Figure 22
Diagram for make-before-break
As shown in
, a CRLSP with 30 M reserved bandwidth has been set up from Router A to Router
D through the path Router A—Router B—Router C—Router D.
To increase the reserved bandwidth to 40 M, a new CRLSP must be set up through the path Router A
—
—Router E—Router C—Router D. To achieve this purpose, RSVP-TE needs to reserve 30 M bandwidth for
the old CRLSP and 40 M bandwidth for the new CRLSP on the link Router C—Router D, but the link
bandwidth is not enough.
Using the make-before-break mechanism, the new CRLSP can share the bandwidth reserved for the old
CRLSP. After the new CRLSP is set up, traffic is switched to the new CRLSP without service interruption, and
then the old CRLSP is removed.
Route pinning
Route pinning enables CRLSPs to always use the original optimal path even if a new optimal route has
been learned.
On a network where route changes frequently occur, you can use route pinning to avoid re-establishing
CRLSPs upon route changes.
Tunnel reoptimization
Tunnel reoptimization allows you to manually or dynamically trigger the ingress node to recalculate a
path. If the ingress node recalculates a better path, it creates a new CRLSP, switches traffic from the old
CRLSP to the new, and then deletes the old CRLSP.
MPLS TE uses the tunnel reoptimization function to implement dynamic CRLSP optimization. For example,
when MPLS TE sets up a tunnel, if a link on the optimal path does not have enough reservable bandwidth,
MPLS TE sets up the tunnel on another path. When the link has enough bandwidth, the tunnel
optimization function can switch the MPLS TE tunnel to the optimal path.
Automatic bandwidth adjustment
Because users cannot estimate accurately how much traffic they need to transmit through a service
provider network, the service provider should be able to do the following:
•
Create MPLS TE tunnels with the bandwidth initially requested by the users.
•
Automatically tune the bandwidth resources when user traffic increases.
MPLS TE uses the automatic bandwidth adjustment function to meet this requirement. After the automatic
bandwidth adjustment is enabled, the device periodically samples the output rate of the tunnel and
