E-4
1/19/05
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000
Priority Routing
Routing Priority Rules
Beta Draft Confidential
Routing Priority Rules
The switch uses the rules in the sections that follow to implement priority routing at
the time of circuit provisioning, trunk-failure recovery, and balance rerouting.
Circuit Provisioning
At the time of provisioning and load balance rerouting, a circuit selects a path ignoring
all circuits with lower-bandwidth priority. In doing so, a circuit will force lower
bandwidth-priority circuits from their selected path until available link bandwidth is
positive and can accommodate circuit bandwidth needs. The following sequence is
used to force circuits from their path:
1. Bandwidth priority order, where lowest-bandwidth-priority circuits are chosen
first. Keep in mind that bandwidth priority values range from zero (0) to 15, with
15 being the lowest priority.
2. Bumping eligibility, where circuits with bumping eligibility disabled are chosen
first. Bumping eligibility values are enabled (highest priority) or disabled (lowest
priority).
3. Equivalent bandwidth (EBW) order, where higher EBW circuits are chosen first.
4. Virtual channel identifier (VCI) order.
Trunk-failure Recovery
VCs always attempt to reroute themselves when a trunk goes down. The switch
software allows a trunk to reach negative bandwidth for circuits recovering from trunk
failure if there is no other available path with positive bandwidth.
Priority routing modifies these rules as follows:
•
A VC of higher-bandwidth priority selects an optimal path in response to trunk
failure without taking into account the bandwidth consumed by circuits of
lower-bandwidth priority. The circuits of lower priority may be forced to use paths
that are not optimal (as defined in the provisioning rules).
•
VCs of lower-bandwidth priority are not allowed to cross trunks where there is at
least one circuit of higher priority and the bandwidth is negative, with the
exception of circuits configured with bumping eligibility enabled. Circuits with
bumping eligibility enabled are allowed to push a trunk to negative bandwidth and
rely on reroute balancing to correct the negative bandwidth at a future time.
Note – These rules work as described when restricted priority routing is disabled.
Содержание CBX 3500
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