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ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter 7 Configuring Virtual Connections
Configuring Soft PVCs and Soft PVPs with Priority
Configuring Soft PVCs and Soft PVPs with Priority
This section describes how to specify priority for soft PVCs or PVPs established over an Inverse Multiplexing
for ATM (IMA) interface. If an IMA link goes down, the performance of all virtual connections requesting
guaranteed bandwidth (CBR, VBR-RT/NRT, ABR/UBR+ with nonzero MCR) can be adversely affected. By
configuring the priority for soft PVCs or PVPs, connections with the highest priority are more likely to be
preserved if an IMA link goes down, while connections with lower or no priorities are cleared, thereby
maintaining bandwidth for the most important connections. A priority of 0 (highest) to 15 (lowest) can be
specified for each soft PVC.
Note Connections of the highest priority may be randomly chosen for clearing if insufficient bandwidth is
available.
If an IMA link goes down, a check is made to see whether the reduced interface bandwidth is greater
than that allocated to connections. If the available bandwidth is below that allocated, the qualifying
signaled VCs are checked to see if they have allocated guaranteed bandwidth. If signaled VCs have
allocated guaranteed bandwidth, they are released on a priority basis until either the bandwidth allocated
is less than that available, or there are no guaranteed-bandwidth signaled VCs.
Note A signaled VC must have allocated bandwidth in order to be released by priority. Therefore, simple UBR
VCs cannot be released by priority. UBR+ VCs, however, have allocated bandwidth and can therefore
be released by priority.
Note Though unaffected by priority configuration, the bandwidth allocated by PVCs is considered when
determining whether or not the bandwidth allocated is below that available.
To specify that soft PVCs can be cleared by priority, perform the following task on an IMA interface:
Configuring a Soft PVC with priority
To configure a soft PVC with priority, perform the following steps:
Command Purpose
Switch(config-if)# atm svc-clear by-priority Specifies that soft PVCs can be cleared based
on priority configurations when bandwidth is
reduced on an IMA interface.
Command Purpose
Step 1
Switch(config-if)# atm soft-vc source-vpi
source-vci dest-address atm-address dest-vpi
dest-vci [enable | disable] [retry-interval [first
retry-interval] [maximum retry-interval]]
[hold-priority priority]
Creates a soft PVC with a priority from 0 (high)
to 15 (low).