After extensive tuning I finally got my Linksys SPA962 IP Phone to work flawlessly with my Zyxel 2602HW modem connected to Telfort.
Configuring the Zyxel 2602HW modem
First you have to make sure the “Enable SIP ALG” setting on the modem is enabled. For some reason a lot of tips on the internet tell you to disable this option on Zyxel modem, but for me this caused the phone to be unable to do a proper the SIP registration.
To enable this feature look under Network\NAT and choose the tab ALG:
Configuring the Linksys SPA962
Now for the Linksys SPA962 IP phone. Not being a VOIP or SIP specialist this took quite some trial and error to get this one right. I went through all the hassle of failed registration, inability to make call to the phone having to be rebooted after every call I made.
Finally it now works perfectly. When you log onto the phone’s build-in web server, make sure you log in as administrator and choose advanced from the menu.
set connection type to DHCP
Make sure the “Register expires” time and the “Proxy Fallback Intvl” values are exactly the same. I am under the impression this was why my phone had to be reset after making a single call (or even just picking up the phone), don’t ask why…
That should do the trick. If for you this still doesn’t work, drop me a comment, perhaps I missed a key setting in the examples above.