E-61/19/05 ATM Services Configuration Guide for CBX 3500, CBX 500, GX 550, and B-STDX 9000
Priority Routing
Priority Routing and Path Cost
Beta Draft Confidential
Priority Routing and Path Cost
By assigning specific bandwidth priority and bumping eligibility to Frame Relay
logical ports and VCs, you can guarantee that the needs of high-priority circuits are
met first. In addition, you can also accommodate circuits where the path cost is not
important. By assigning a routing priority, you can guarantee that when a link fails or
network congestion exists, the higher-priority circuits are given preference in the
network over circuits with a lower priority.
Priority Routing and Path Cost Example
There are two paths (Path 1 and Path 2) between a pair of nodes (A and B). The cost of
Path 1 is 100, while the cost of Path 2 is 200. Multiple PVCs within the network are
defined with the following priority routing settings: bandwidth priority 2, bumping
eligibility enabled, and restricted priority routing disabled. These VCs use all of the
bandwidth on the Path 1 link. Without priority routing, additional VCs are forced to
use Path 2, which could involve higher delays and more hops.
With priority routing, you can define additional circuits between A and B with a
Bandwidth priority of zero (0) and bumping enabled. The switch running the
priority-routing software can detect that Path 1 is entirely populated by the circuits
with the bandwidth priority 2 and bumping enabled. The switch then forces enough of
these circuits (priority 2, bumping eligibility enabled) from Path 1 to ensure that every
trunk in Path 1 has enough bandwidth to satisfy the QoS of the highest-priority
(bandwidth priority zero (0), bumping eligibility enabled) circuits. As a result, some
priority 2-enabled circuits are forced to Path 2.
Restricted Priority Routing and Path Cost Example
There are two paths (Path 1 and Path 2) between a pair of nodes (A and B). The cost of
Path 1 is 100, while the cost of Path 2 is 200. Multiple PVCs within the network are
defined with the following priority routing settings: bandwidth priority 10, bumping
eligibility enabled, and restricted priority routing enabled. These VCs use all of the
bandwidth on the Path 1 link.
With restricted priority routing enabled, you can define additional circuits between A
and B, with bandwidth priority of zero (0) and bumping eligibility enabled. These
circuits will establish over the higher cost trunk (Path 2). With restricted priority
routing enabled, new circuits are not allowed to bump existing active circuits.
If you disable Path 2, the circuits with bandwidth priority of zero (0) will re-establish
over Path 1, bumping the lower-priority circuits. With restricted priority routing
enabled, circuits are allowed to bump other lower-priority circuits only during
trunk-failure recovery.
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