Why in infinity call through vpn one-way audibility?

Question

Telephony

There is a call center. between the main office where the server is infinity and the call center vpn l2tp tunnel on mikrotik. The client on the computer connects to the server normally.
The employee took the computer home, the infinity program connects to the server via vpn. But the connection is one-way, I hear the dispatcher, but she doesn’t hear me, I tried pptp, sstp connections, set up openvpn (upd) on a separate centos server, the client also connects to it, I don’t hear and I don’t hear me.

Answer 1

Because somewhere NAT.