Why can't one computer make a LAN call to another?

Question

Telephony

There are two local computers:
One computer can make calls (via local IP), the other computer writes either Bad Request or Cannot get IP Address of the called host when you call a neighbor PC by IP. Prog: Microsip, reinstalled, it still makes no sense. I think the problem is somewhere in the politicians? What could be the problem in general?

Answer 1

pingay
telnet
nmap ports

Answer 2

Chorus: Wireshark, Wireshark!!!