3rd party BTS is connected to RTN910 through 1xE1, and is using the same E1 for synchronization. After commissioning and configuration, the BTS was up and running, but after one day, it started to drop calls.
No alarms on RTN or BTS.
It was quickly discovered that the RTN910 was using the internal clock source, and no external clock sources was configured. The configuration was changed such that the RTN910 traces the clock from the upstream RTN950 through the microwave link.
As the problem still existed, we checked the retiming mode of the E1 port. According to the product documentation, “Tributary retiming is a function that helps to reduce the jitter of a PDH signal after the signal travels through an SDH network. When this function is used, the PDH service loses its original timing information.” This parameter was set to “Retiming Mode of Cross-Connect Clock”, which means it will retime the PDH signal with the clock the cross-connect unit. We changed this to “Normal”, so that the PDH signal would keep it original timing, and after this change, the BTS did not drop any more calls.
Check the synchronization configuration and status of the Huawei NEs, starting with the upstream NE.
Check the retiming mode of the E1 port.
Make sure the proper synchronization sources are configured, and use the retiming mode with care.