How to limit the number of SIP calls from PC(x-lite, 3cx, zoiper)?

Question

Asterisk

Hello, an idea arose, along with the usual telephony provided through voice gateways, to provide customers with a parallel "soft" phone on a PC (x-lite, 3cx, zoiper). PBX is raised on FreePBX, is in a gray network, there is no access to it from outside. But the question of security arises, how to correctly limit the number of incoming and outgoing calls through a softphone, in case an unscrupulous client comes across and raises his PBX for the call center, or the admin takes offense at the employer and makes some calls to Israel through the tunnel to the working PC through us. For our part, we can see this only in the CDR, but at that moment there will already be a bill for a round sum, which the client will refuse to pay. Have you done something like this or have any thoughts on this?

Answer 1

Limit the number of simultaneous calls per peer - 1 or 2 lines - there will no longer be a large PBX on the client side and the number of simultaneous malicious calls will decrease. Also, you can make a list of allowed SIP clients and block calls from any other user_agent. Not a very effective defense, but one more level will not hurt.
The rest is a flight of fancy based on CDR data: a certain number of foreign calls of a certain duration with a certain frequency - a block with a notification to the client with a password change. If the client complains about permanent blocking - increase this limit for him or disable the limit under his responsibility (with an official letter from the client).

Answer 2

there is billing for that