Possible causes included:
1. Configurations were incorrect.
2. BRASs' processing mechanism had a bug.
3. Third-party modems had problems.
To address the issue, Huawei performed the following operations and observed the following information:
1. Checked the configuration and found that the configuration was correct.
2. Verified that the BRAS processing mechanism was normal.3. Asked the customer to configure port mirroring on the BRAS and UA5000 to capture packets. According to the captured packets, the third-party modem transmitted four PADR packets upon receiving four PADO packets and did not respond to the BRAS during LCP negotiation. ME60 transmitted PADT packets after failing to receive responses for three times and released sessions.