The subscriber is busy, how to fix it?

Question

System administration

All day. The essence of the problem: when you call an external number, the PBX says that the subscriber is busy. After restarting the VoIP gateways everything works well, for the time being. Sometimes they can’t get through to us, it just cuts off.
Panasonic TDA200
VoIP Yeastar ta800(8 incoming, 8 outgoing)
There are no chippers.
Where to dig?

Answer 1

перепадов напряжения нет? обычно атс это не людят