I use a Gigaset N300-IP base station with the TalkTalk HG635 Super Router on a fibre line. It's been successfully in use for well over a year for outgoing calls. Not any more though. Maybe 6-8 weeks ago it just stopped. That is it simply will not register with the sip address.
(For those that are unfamiliar, the N300-IP box provides landline and voip with up to 6 dect phones.) It's set up with one of the Dellmonte stable voip services (Discountvoip).
The HG635 has mostly default settings except I use my own DHCP and DNS. A cable is used to connect the N300-IP to the router. I have the RTSP ALG and SIP ALG enabled.
The HG635 is Hardware 1.01 and firmware v1.06t
The N300-IP is recognised by the router and I have normal local web access to it's control page.
The N300-IP otherwise functions normally.
I've tried reverting to all default settings, switching the RTSP and SIP both off and on, and doing a factory restore.
I've tried another Dellmonte sip service Voipcheap.
Using CsipSimple on Android, through the router WiFi, discountvoip registered straightaway.
I've tried another N300-IP.
I've tried opening port 5060 on the router
I've tried enabling DMZ on the N300-Ip's net address.
So far nothing has made any difference. Any ideas anyone?