In one NGN carrier network, when the traffic on 155M ATM is around 25Mbps, the PING loss would happen. But on some others 155M links, PING is smooth with just several mega traffic. When PING loss took place, the quality of voice became very nosiy and bad, even the other side cannot hear clearly.
The PING loss reached 10 percent when the traffic was about 45Mbps.
1. Transmission person checked the quality using hardware loop method, the link is quite good.
2. We checked the configuration. There's no obvious wrong about it. In consideration of the quality of voice, the NGN engineer set the nrt-vbr mode for this service on ATM port.
3. We changed patch cord and ATM port from original one to a new one, but this problem still existed. There should be no wrong on physical link.
4. Because customer used NE40 to test fast PING, We were afraid that NE40 system would drop some PING packets. But after checking CPU system-bucket, we didn't find any dropped packets. It approved that the loss packets were not dropped by CPU of NE40.
5. With the guide of RND, we changed the service mode of ATM from nrt-vbr to ubr. After changing, everything is OK.
6. Now we can make a conclusion we'd better use ubr mode for voice service because there's some defect in designing of ATM hardware.
1. Transmission cause.
2. Physical error, including patch cord and ATM port.
3. CPU of NE40 dropped the PING packets.
4. Configuration error.
1. We'd better not deploy VBR or ABR for voice service on ATM port. Ubr mode is best option for it.
2. We'd better not test fast PING with NE40.