H3C Technologies H3C S7500E Series Switches - Manual (Page 88)

3-6
Soft state is a mechanism used in RSVP-TE to periodically refresh the resource reservation state on a
node. The resource reservation state includes the path state and the reservation state. The path state
is generated and refreshed by the Path message, and the reservation state is generated and
refreshed by the Resv message. A state is to be removed if no refresh messages are received for it in
certain interval.
2) Resource reservation style
Each LSP set up using RSVP-TE is assigned a resource reservation style. During an RSVP session,
the receiver decides which reservation style can be used for this session and thus which LSPs can be
used.
Currently, two reservation styles are available:
z
Fixed-filter style (FF) where resources are reserved for individual senders and cannot be shared
among senders on the same session.
z
Shared-explicit style (SE) where resources are reserved for senders on the same session and
shared among them.
At present, SE is only used for make-before-break because multiple LSPs cannot be present on the
same session.
Make-before-break
Make-before-break is a mechanism to change MPLS TE tunnel attributes with minimum data loss and
without extra bandwidth.
Figure 3-1 Diagram for make-before-break
Figure 3-1 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 Mbps.
If 40 Mbps path bandwidth is requested, the remaining bandwidth of the Router A → Router B →
Router C → Router D path will be inadequate. The problem cannot be addressed 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 may 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