Please help to emulate a 56k connection

I know this is a not secure configuration, but they are only vm for testing, and I can use a closed network to avoid internet access to this old and insecure vm.
I have sucesfully emulated a direct serial connect with a windows client(Windows 2000) and a Centos8 dial-in server(mgetty+pppd) between two virtual machines(Windows 2000 is client and Centos8 is server), using libvirt in Slackware Host.
Now I want to emulate a old ppp connection with linux client(Mandriva Linux) using kppp and the same Centos8 server.
I don't had any 56k modem, but I know a project exist to emulate a modem and is called tcpser, I have configured the Centos8 server to run tcpser
and the Windows Client or Mandriva Client are directly connected via a fake serial line(is a socket, libvirt can emulate the serial line, I have successfully tested with the previous direct-line configuration).
If interested this is the fake serial line xml(the client use connect, the "server" use bind)

Code:Windows

<serial type="unix">
<source mode="connect" path="/tmp/ppp.sock"/>
<target type="isa-serial" port="0">
<model name="isa-serial"/>
</target>
<alias name="serial0"/>
</serial>

Centos

<serial type="unix">
<source mode="bind" path="/tmp/ppp.sock"/>
<target type="isa-serial" port="0">
<model name="isa-serial"/>
</target>
<alias name="serial0"/>
</serial>On Centos I run the tcpser program, which create a "bridge" between serial and telnet server make a connection

Code:tcpser -d /dev/ttyS1 -s 38400 -l 7 -tsSiI -i "s0=1" -n"010010102=centos.domain.private:23"I have tried a old Mandriva client and a Windows 2000 client with those results.

Windows: hyperterminal works perfect, i connect to the fake 01000102 number, and login via telnet(I will try also ssh in the future..)
PPP-connection: compose ok, connect ok..but fail with error 17 loopback !
:(

Mandriva: kppp, connect and fail with error 17

This is my ppp configuration, of course the user is configured to have a pppd "shell" so at first login it create the ppp interface, with mgetty and direct serial line works perfect, is impossible to run pppd?

/etc/ppp/options

Code:debug
login
default-asyncmap
require-pap
proxyarp
ktune
ms-dns 192.168.0.4
nomagic/etc/ppp/options.ttyS1

Code:local
lock
nocrtscts
192.168.100.1:192.168.100.2
netmask 255.255.255.0
debug
noauth
nomagic/etc/ppp/pap-secret
Code:# client server secret IP addresses
myuser * mypassword *