How do I set up city calls from an Avaya phone?

Question

Telephony

Hello. There are 2 automatic telephone exchanges of Avaya. 2 avaya ip-dect handsets created on PBX 1, 1 avaya desk phone created on PBX #2. All phones go to the city from one city number. The problem is that the landline phone lost the ability to call landline numbers, at the moment when any of the IP-DECT handsets is talking. What could be the problem and where to dig to solve it?

Answer 1

What is the trunk for communication with the city and how much time slot is there?