T200 expiry means that the LAPD frame is sent from point A to point B on Abis, but without acknowledgment from point B.
If the frame is not acknowledged, it means it has not be received. Therefore the point A will retransmit the frame up to N200 times.
At N200+1 times, the point A will stop trying –> drop.
Now, how many reasons do you for not having an ACK from point B ?
A/ either the link is broken, and point B never received the initial data
B/ point B is down (or in a faulty state) and doesn’t receive/ack the frames.
restart your processes on each end, investigate your Abis links, swap your control boards… there is not much you can do.
It’s either software pb or hardware pb.