A ISDN terminal can 6B in two-way and connect with MCU, other sites can’t see this site’s image by MCU.
Diagnose by VP8000 system, there is a high bit error in the direction from ISDN terminal to MCU. But there is no BER tester in terminal, so we can’t find the bit error reason by rule and line. So we use fault exclusion method.
We use a digital phone with one of the ISDN number call for MCU, the quality is poor. So we can determine that it’s the transmission link bring bit error.
In the same way, we call from terminal to the office number, the quality is still poor. We can determine that it’s the local link bring bit error.
Check the link port between terminal and office, and check if there is any strong interference source. So we eliminate these two reasons.
We find there is an access server in the ISDN link from terminal to office. The fault disappears after replacing a user board in terminal.
The user board of access server brings bit error.