Fixed-filter (FF) style—Resources are reserved for individual senders and cannot be shared
among senders on the same session.
Shared-explicit (SE) style—Resources are reserved for senders on the same session and shared
SE is only used for make-before-break because multiple LSPs cannot be present on the same session.
Make-before-break is a mechanism to change MPLS TE tunnel attributes with minimum data loss and
without extra bandwidth.
Figure 26 Diagram for make-before-break
presents a scenario where a path Router A—Router B—Router C—Router D is established with
30 Mbps reserved bandwidth between Router A and Router D. The remaining bandwidth is then 30
If 40 Mbps path bandwidth is requested, the remaining bandwidth of the Router A—Router B—Router
C—Router D path is inadequate. You cannot address the problem by selecting another path, Router A
—Router E—Router C—Router D, because the bandwidth of the Router C—Router D link is inadequate.
To address the problem, you can use the make-before-break mechanism. It allows the new path to share
the bandwidth of the original path at the Router C— Router D link. Upon creation of the new path, traffic
is switched to the new path and the previous path is torn down. This helps avoid traffic interruption
RSVP-TE uses RSVP messages with extensions. The RSVP messages are as follows:
Path messages—Transmitted along the path of data transmission downstream by each RSVP sender
to save path state information on each node along the path.
Resv messages—Sent by each receiver upstream towards senders to request resource reservation
and to create and maintain reservation state on each node along the reverse of data transmission
PathTear messages—Sent downstream to remove the path state and related reservation state on
each node along the path.
ResvTear messages—Sent upstream to remove the reservation state on each node along the path.
PathErr messages—Sent upstream to report Path message processing errors to senders. They do not
affect the state of the nodes along the path.
ResvErr messages—Sent downstream to notify the downstream nodes that an error occurs during
Resv message processing or reservation error occurs as the result of preemption.