Priority Routing
About Priority Routing
ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000 1/19/05E-3
Beta Draft Confidential
To use priority routing, you provision the following options for new PVCs and SVCs:
• Bandwidth priority — A value from 0 – 15, where zero (0) indicates the highest
priority. For PVCs, the default value is zero (0); for SVCs, the default value is
eight. The bandwidth priority setting is used in route calculations.
• Bumping eligibility — Enables (PVC default) or disables (SVC default) bumping
eligibility for the circuit. This option is valid only for non-real time circuits, based
on QoS classes. Real time circuits ignore this setting.
• Restricted Priority Routing — Enabled (default) provisions new circuits at the
lowest-bandwidth priority, regardless of configured higher-bandwidth priority and
bumping eligibility settings. You must disable this option if you want to use the
configured bandwidth priority and bumping eligibility settings for newly
provisioned circuits. When enabled, restricted priority routing functions only
during initial setup and load balance rerouting; higher-priority circuits can bump
other circuits only during trunk-failure recovery.
The default settings for bandwidth priority, bumping eligibility, and restricted priority
routing are the recommended settings for provisioning new circuits. See “Configuring
SVC Attributes” on page 17-2 and “User Preference Attributes” on page 10-26 for
more information about configuring these options.
Using Restricted Priority Routing
Restricted priority routing works in the following additional ways:
• If restricted priority routing is disabled, a non-real time circuit that has been
bumped and has bumping eligibility enabled will become active whether sufficient
bandwidth exists. If bumping eligibility is disabled, the circuit remains in retry
mode until sufficient bandwidth is available.
• If restricted priority routing is enabled, a non-real time circuit that has been
bumped remains in retry mode until sufficient bandwidth is available, regardless
of the bumping eligibility setting (disabled or enabled).
• Restricted priority routing allows circuits to become active only if sufficient
bandwidth is available in the network. Load balancing reroutes circuits to optimal
paths that do not require bumping existing circuits.
• Trunk-failure recovery uses configured bandwidth priority and bumping eligibility
settings, not restricted priority routing. When restricted priority routing is enabled,
higher priority circuits can bump other circuits only during trunk-failure recovery.
• If circuits fail to reroute because of negative bandwidth, you can disable restricted
priority routing for individual circuits. These circuits will then use their
configured bandwidth priority and bumping eligibility settings to find optional
paths, without causing large-scale network rerouting.
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