Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

6m PVC utilisation over ATM


I am trying to check how much traffic I can send across an ATM link (6m PVC). I have tested using VOIP traffic (with no QoS configured) and have seen upto 4m worth of traffic before packet drops are being seen (no CRC / errors etc seen).

BT have also checked their circuit and confirm that their is nothing wrong physically, or with the PVC. They were not however able to prove 6m worth of traffic could be passed.

My question therefore is, given I have a 6m PVC configured across the ATM circuit, what is the maximum level of traffic I am realistically going to see?

Details of connection:

interface ATM1/0.1 point-to-point

bandwidth 6000

ip address

ip directed-broadcast

ip ospf cost 1000

pvc CardiffG-Havant 1/32

protocol ip broadcast

protocol ip

vbr-nrt 6000 6000

tx-ring-limit 3

oam-pvc manage 3

encapsulation aal5snap

The routers either end are: 7206VXR and 7507 (RSP4).




Re: 6m PVC utilisation over ATM

The only VCs eligible for idling are those with a current 1-second activity rate less than or equal to the value configured by the ip pim minimum-vc-rate interface configuration command on the ATM interface. Activity level is measured in packets per second (pps).

The VC with the least amount of activity below the configured ip pim minimum-vc-rate pps rate is idled.

If the ip pim minimum-vc-rate command is not configured, all VCs are eligible for idling.

If other VCs are at the same activity level, the VC with the highest fanout (number of leaf routers on the multipoint VC) is idled.

The activity level is rounded to three orders of magnitude (less than 10 pps, 10 to 100 pps, and 100 to 1000 pps). Therefore, a VC that has 40 pps activity and another that has 60 pps activity are considered to have the same rate, and the fanout count determines which one is idled. If the first VC has a fanout of 5 and the second has a fanout of 3, the first one is idled.

Idling a VC means releasing the multipoint VC that is dedicated for the multicast group. The traffic of the group continues to be sent; it is moved to the static map VC. Packets will flow over a shared multipoint VC that delivers packets to all PIM neighbors.

If all VCs have a 1-minute rate greater than the pps value, the new group (that exceeded the ip pim vc-count number) will use the shared multipoint VC.

New Member

Re: 6m PVC utilisation over ATM

So given there's only a single VC on this ATM, and its configured for 6m, what bandwidth level should be seen at its maximum rate?