We have 4 7609S routers, 2 pairs, connecting 2 sites via E1s. The SIP in use is SIP200 with 8-port Channelized T1/E1 SPA.
While the causes/solutions to the CRC errors are pretty much available on the documentation, we have checked the physical connections and replaced them, the service provider has made loops towards the transmission network and it was okay, we checked the earthing for the chassis.
Finally we did a test where we connected the 2 adjacent 7609s to each other through a UTP cable at one of the E1 controller ports and still we saw CRC errors on that controller!! meaning that the problem is not in the transmission and possibly in the routers.
Could it be something faulty in the SPA, FPD package, or anything else? Any suggestions are highly appreciated.