SIP behind Routerboard Problem

RouterOS General
1

Hi,
I have a site configured ADSL Modem → Router Board 750 → Fritzbox LAN1
with a number of IP phones on the network as the Fritzbox.

I have a basic configuration in the 750 masquerading the phone network and passing UDP protocols.
My problem is every thing works except I cannot call numbers that begin with 3 i.e. 3890xxxx which has area code added by the fritz box to 073890xxxx
Numbers that begin with other numbers work and so do mobile numbers.
Calls to numbers that begin wit 3 do actually get through - they ring at the other end but the caller does not hear ring tone and if the call is answered, the receiver can hear the caller speak but the caller cannot hear anything said by the receiver. The call is not terminated.
Any thought son cause or solution appreciated.
Thanks

2

I do not know but my gut reaction is that it is a router issue. Try bridging all of the traffic from your upline to the sip device without using NAT and see if the issue persists. This would bipass the SIP helper that is used when the router is performing NAT. I would suspect that you will find that the issue is a dialplan or sip routing issue with your sip provider not with something in your router.

3

Or first just try to disable firewall/service port sip

4

I agree with spire2z. In my case I disabled sip helper ( ip - firewall - service ports - disable sip) and sip started to work.
May be after this you need to reboot router and sip device to flush existent rules on all devices.
You need also switch on UPNP may be.