Alcatel-Lucent 7450 Manual page 35

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A secondary or standby secondary path is initially signaled with its configured bandwidth. Setup
for the secondary path is triggered only when the active path goes down or becomes degraded (e.g.
due to FRR or preemption). An auto-BW triggered bandwidth adjustment (auto bandwidth MBB)
only takes place on the active path. For example, if an auto-BW adjustment occurs on the primary
path, which is currently active, no adjustment is made at that time to the secondary path since that
path is not active.
When the active path changes, the current_bw is updated to the operational bandwidth of the
newly active path. While the auto-BW MBB on the active path is in progress, a statistics sample
could be triggered, and this would be collected in the background. Auto-bandwidth computations
will use the current_bw of the newly active path. In case the statistics sample collection results in
a bandwidth adjustment, the in-progress auto-BW MBB will be restarted. If after five attempts, the
auto-BW MBB fails, the current_bw and secondary operational BW remain unchanged.
For a secondary or standby secondary path, if the active path for an LSP changes (without the LSP
going down), an auto-BW MBB will be triggered for the new active path. The bandwidth used to
signal the MBB will be the operational bandwidth of the previous active path. If the MBB fails, it
will retry with a maximum of 5 attempts. The reserved bandwidth of the newly active path will
therefore be its configured bandwidth until the MBB succeeds.
For a secondary path where the active path goes down, the LSP will go down temporarily until the
secondary path is setup. If the LSP goes down, all statistics and counters are cleared, so the
previous path operational bandwidth is lost. That is, the operational BW of a path is not persistent
across LSP down events. In this case, the there will be no immediate bandwidth adjustment on the
secondary path.
The following algorithm is used to determine the signaled bandwidth on a newly active path:
1. For a path that is operationally down, signaled_bw = config_bw.
2. For the active path, if an auto-BW MBB adjustment is in progress, signaled_bw = previous
path operational BW for the first 5 attempts. For the remaining attempts, the signaled BW =
operational BW.
3. For an MBB on the active path (other than an auto-BW MBB), MBB signaled BW = opera-
tional BW.
4. For an MBB on the inactive path, MBB signaled BW = configured BW.
If the primary path is not the currently active path and it has not gone down, then any MB uses the
configured BW for the primary path. However, if the configured BW is changed for a path that is
currently not active, then a config change MBB is not triggered.
7450 ESS MPLS Guide
active path: the path (primary or secondary) the LSP currently uses to forward traffic
signaled BW: the new BW value signaled during an MBB
MPLS and RSVP
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