E-21/19/05 ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000
Priority Routing
About Priority Routing
Beta Draft Confidential
Network Convergence Time
Priority routing introduces network convergence time into the network. When you
configure a logical port’s PVC or SVC routing priority, you specify the bandwidth
priority (or level of importance) and bumping eligibility (enabled or disabled) of each
PVC or SVC in the network. The lower the number for bandwidth priority, the higher
the priority. During circuit provisioning or trunk-failure recovery, higher-priority
circuits can bump existing lower-priority circuits. The network attempts to re-establish
the lower-priority circuits, which may cause further bumping of still lower-priority
circuits. The period of network convergence required for the network to stabilize is
directly proportional to the number of priorities defined in the network.
You can maintain network stability by using restricted priority routing to override
configured bandwidth priority and bumping eligibility settings when you provision
new circuits (PVCs and SVCs). Restricted priority routing uses the lowest bandwidth
priority during initial circuit setup and load balance rerouting, regardless of configured
higher-bandwidth priority and bumping eligibility settings.
Specifying Routing Priorities
When you configure a logical port’s PVC or SVC routing priority, you specify the
bandwidth priority (or level of importance) and bumping eligibility of each PVC or
SVC in the network. To override configured bandwidth priority and bumping
eligibility settings for new circuits, you must enable (default) the restricted priority
routing option.
If you do not override the default values for bandwidth priority (highest priority for
PVCs; eight for SVCs) and bumping eligibility, all PVCs in the network have the same
routing priority, and all SVCs in the network have the same routing priority. If your
network uses only PVCs, or only SVCs, priority routing is, in effect, turned off, since
the priority of all circuits is the same.
However, if you prioritize circuits and disable restricted priority routing in your
network, the switch assigns circuits with the highest priority to the lowest-cost paths
through the network. These high-priority circuits are guaranteed full bandwidth
wherever possible. Circuit prioritizing occurs at the cost of the lower-priority circuits.
Note – If your network uses both PVCs and SVCs, priority routing is turned on in
the network because the default priority settings are different for each type of
circuit. If you do not want priority routing to function in your network, Lucent
recommends that you set the bandwidth priority for all SVCs to match the PVC
bandwidth priority (highest).
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