TP-Link MR200 voip (sip) no sound can be heard

[miloslava]

There is no sound from the handset in the original firmware or in Openwrt. The microphone goes, the other party can hear me, but I can't hear her. I have a TP-Link MR 200 v1.1 O2 router, but it appears to be v1.
I tried the instructions and installed viz.:

opkg update
opkg install kmod-nf-nathelper-extra
/etc/init.d/firewall restart

cat << EOF >> /etc/sysctl.conf
net.netfilter.nf_conntrack_helper=1
EOF
/etc/init.d/sysctl restart

Then I found this code to try out:
sysctl net.netfilter.nf_conntrack_helper; \
iptables-save -c -t raw | grep -e PREROUTING -e sip

The terminal message is:

sysctl net.netfilter.nf_conntrack_helper; \
> iptables-save -c -t raw | grep -e PREROUTING -e sip
net.netfilter.nf_conntrack_helper = 1
-ash: iptables-save: not found

Please don't you know where the error could be, what, for example, to enable in the firewall?

[StepSis]

You may want to check this:

Need help setting up voip

The audio packets must be going to another server. You'll need to route to that server through the voip wan. Run a tcpdump on UDP packets coming from the phone. After dialing there will be a stream of UDP carrying the voice.

[miloslava]

Thanks for the tip, I'll try it. It works if I connect the mobile data via wifi hostpot and do wwan in openWRT. It also works on another Netgear WNDR 3700 v1 router, which I checked has the same settings. So there is a problem somewhere between the transmission between OpenWRT and part of the system from TP-Link, the author writes "The included modem in this device is running Android OS and has a hidden" WAN usb0 and WAN6 usb0.
There was a problem even with the original firmware, where it was not possible to operate even according to the TP-Link instructions, and I thought that OpenWRT would allow it.

[miloslava]

Calling works when using Proton VPN on mobile. That's the only solution TP-Link has it broken even with the original firmware version. It's a bad company.