Why the state of the interface alternates between Up and Down after an AR+8E1/T1-F card is used to connect to the peer end in the replacement of a Cisco+8E1/T1-F card

This problem occurs because E1-F interfaces support two frame formats when working in framed mode: CRC4 and NO-CRC4.
The frame format of E1-F interfaces of Huawei devices is NO-CRC4 by default. However, the frame format of E1/T1-F interfaces of Cisco devices is CRC4 by default. Therefore, after the Cisco card is replaced by the Huawei card, the frame formats on both ends become different, so that the state of the interface alternates between Up and Down after the Huawei device interconnects with the peer end. Before using an E1/T1-F card, run the fe1 frame-format { crc4 | no-crc4 } command to configure the frame format of the E1-F interface, ensuring that the frame formats on both ends are consistent.

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