IGX UXM bandwidth weirdness

[rraja2006]

We have a pair of IGX 8420s connected over a NTM E1 trunk. Over this trunk several 24-channel UVM connections are routed. Each 24-channel connection uses up approx 700packets/sec using g729ar8v compression.

We are trying to switch the E1 trunk to a UXM card. When we do this, the number of packets/sec by a 24 channel UVM connection remains the same value ie 700 packets/sec. This is unexpected since we expect each UVM connections usage to drop by about 50% (to about 350cps) since a ATM cell is 53 bytes and FP cell is 20 bytes.

Moreover, existing data/fr connections behave as expected. On a NTM trunk a 300K fr connection uses approx 1500fps while on a UXM trunk that drops to about 786cps.

Is there something I am missing regarding the UVM connections? Is this value configurable somewhere?

Thanks for any assistance.

Raja

[pkernan]

Hello Raja,

It sounds like you may need to adjust the cnfcmb values for your voice traffic. The basis of seeing this is due to the fact that we have to put fastpackets into ATM cells.

Manipulating the values seen in the cnfcmb command will change how long we wait for a fastpacket before the ATM cell is forwarded on the trunk. So you want to change the value to ensure that you are getting 2 Fastpackets per ATM cell. http://cisco.com/univercd/cc/td/doc/product/wanbu/bpx8600/9_2/92cmdref/92cmd10.htm#23195

Hope this helps.

Kind regards,

Pat

[rraja2006]

Thank you for that link. I will be attempting that today. I see the default value for voice is set to 2 (*125). Is this pretty much a trial and error setting (trying values from 3 to 255) or is there a magic value that makes us get 2 Fastpackets per ATM cell?

Thanks

Raja

[rraja2006]

To follow up on my own post, I set the value to 161 based on Cisco docs which fixes this issue

Thanks

Raja