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IP packet loss on ATM OC3

IP packet loss on ATM OC3

Hey all,

Got a problem I can't figure out. We've got an ATM OC3 connection into the local ILEC's cloud with a bunch of PVCs built to customers. Just about every single customer on this OC3 is having bandwidth problems and problems with packet loss.

If we do a ping via IP across the PVC with any packets larger than 500 bytes, we see anywhere between 3% and 10% packet loss. This does not happen with our ATM DS3s in the same router. There aren't any interface errors accumulating, and the ILEC has tested the circuit clean to a loop in our router. If we do end-to-end OAM echos on each PVC everything turns up fine with no cell loss. I'm really at a loss as to what the problem could be, but basically the ILEC is telling us we must have a problem with our Cisco config.

Non-working ATM OC3 sample config:
interface ATM1/1/0
bandwidth 155000
no ip address
load-interval 30
atm ilmi-keepalive

Sample of PVC config from non working OC3:
interface ATM1/1/0.4 point-to-point
bandwidth 20000
ip address x.x.x.x
pvc 1/103
ubr 20000
encapsulation aal5snap

Ping results from the router:
Sending 50, 1000-byte ICMP Echos to x.x.x.x, timeout is 2 seconds:
Success rate is 96 percent (48/50), round-trip min/avg/max = 1/2/4 ms

Sample config of working ATM DS3 in same chassis:
interface ATM4/1/0
bandwidth 45000
no ip address
load-interval 30
atm scrambling cell-payload
no atm ilmi-keepalive

Sample of PVC from working DS3:
interface ATM4/1/0.12 point-to-point
ip address x.x.x.x
pvc 1/53
ubr 44000
encapsulation aal5snap

Ping results:
Sending 50, 1000-byte ICMP Echos to x.x.x.x, timeout is 2 seconds:
Success rate is 100 percent (50/50), round-trip min/avg/max = 4/4/8 ms

I'd be very appreciative of any troubleshooting suggestions anyone may have.

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