3Com S7902E, Configuration Manual

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1-6
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 1-1
Diagram for make-before-break
Figure 1-1 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 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: