AR28 router and the router of C enterprise are connected through E1 link. The intermediate link is normal, but physical layer is down.
1. Both devices are connected through 2M interface and the physical layer can be up. The intermediate link can be ironed out.
2. Check configuration and it is found that link layer of the peer is HDLC and our device is PPP. Adjust them as the same and the physical layer is still down.
3. Later it is found that frame format of the interface on the device of C enterprise is CRC4. By default frame format of E1 interface of our device is no-crc4. Change frame format as crc4 and physical layer and link layer are up.
1. The physical layer is down, intermediate link may be problematic.
2. The configuration may be problematic.