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FAQ
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RF Unit CPRI Interface Error alarm in Huawei DBS 3900

Posted at February 22, 2018 in by
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Understanding CPRI

In modern mobile networks, the Common Public Radio Interface (CPRI) standard is based on the fronthaul communication between the baseband unit (BBU) and remote radio heads (RRH). This high-speed, low-latency interface is crucial for maintaining optimized performance and synchronization in 4G and 5G networks.

An issue that can disrupt this communication is the “RF Unit CPRI Interface Error” that can be encountered in the Huawei DBS 3900 base station. This error typically results in a non-operational CPRI link, which means the radio unit cannot function properly.

 

An Issue That Has Been Observed

The issue was observed when a CPRI 2.67G-SFP-2D transceiver was used in the DBS 3900. These transceivers are compatible in terms of form factor and data rate, however, they have internal configuration settings stored in the EEPROM memory map that conflict with Huawei’s requirements.

 

Specifically, the receiver slew rate and receiver filter functions are enabled by default. These settings are meant to fine-tune the signal performance under certain conditions, but unintentionally limit the maximum supported bandwidth to 2.25 Gbps – below the 2.4576 Gbps typically used in CPRI links.

 

When the DBS 3900 attempts to establish a CPRI link over 2.25 Gbps using the transceiver, the mismatch of bandwidth causes a failure in the data transmission, triggering the “CPRI Interface Error.” As a result, the link becomes non-functional, and the RF unit fails to communicate with the baseband unit.

 

A Solution for the Issue

To resolve this issue, the EEPROM must be reprogrammed to disable the slew rate and filter settings, allowing the full speed data rate beyond the 2.25 Gbps. With this in mind, we can provide the full support of CPRI at 2.4576 Gbps on this family of transceivers.

 

Key Takeaway

While SFP modules may appear identical, their internal firmware configurations and settings stored in the EEPROM can significantly affect the compatibility with the equipment. For Huawei DBS 3900, using a transceiver with the improper settings may lead to major connectivity problems. It is crucial to validate and properly select the CPRI transceiver to ensure a stable network infrastructure.