Priority Routing
Routing Priority Rules
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/05E-5
Beta Draft Confidential
• VCs of higher priority may push a trunk to negative bandwidth if there are no
more circuits of lower priority to force off the trunk. In this case, all of the
lower-priority circuits (excluding circuits with bumping eligibility enabled) are
forced off the trunk. Circuits configured with bumping priority enabled are given
special permission to share the negative bandwidth trunk with higher-priority
circuits until the reroute balancing corrects this at a future time.
Balance Rerouting
Balance rerouting is a switch function that periodically tests the efficiency of each VC
route. A circuit that was rerouted due to trunk failure may not be on the most optimal
path at any given time or may be traversing a negative bandwidth trunk. Balance
rerouting corrects these conditions by rerouting the circuit to a new path.
Priority routing modifies the switch balance-rerouting functions so that a circuit with a
higher bandwidth priority is given an optimal path, and the bandwidth used by the
lower-priority circuits is not considered by the switch. For this reason, circuits of
lower priority may be forced onto a path that is not optimal. See “Circuit
Provisioning” on page E-4 for details about path selection.
Interoperability With Previous Releases
To use circuit-routing priority in your network, the following interoperability
restrictions apply:
• All switch software must be at least Release 04.01.00.00 or higher for
B-STDX 9000 switches.
• On a trunk, if either end resides on a 04.01.00.00 B-STDX 9000 switch, the trunk
treats all PVCs equally (assumes all have a 0,0 priority).
On a circuit, if either end belongs to a 04.01.00.00 B-STDX 9000 switch, the circuit is
automatically assigned a 0,0 priority. The NMS does not support any routing priority
other than 0,0 on switches running Release 04.01.00.00 or lower.
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