H3C Technologies H3C S10500 Series Switches - Manual (Page 101)

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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; 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 which LSPs can be used.
The following reservation styles are available:
• Fixed-filter style (FF) where resources are reserved for individual senders and cannot be shared
among senders on the same session.
• Shared-explicit style (SE) where resources are reserved for senders on the same session and shared
among them.
NOTE:
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 26 Diagram for make-before-break
Figure 26 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 is 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 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
effectively.
RSVP-TE messages
RSVP-TE uses RSVP messages with extensions. The following are RSVP messages:
• 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.