[Asterisk-Users] Timing out on Registration

[Christian Grams]

Hello everybody...
I´m having huge problems getting Asterisk registered to my german VoIP
Provider.

I get the following error message:
NOTICE[8308]: chan_sip.c:5247 sip_reg_timeout: -- Registration .....
timed out, trying again (attempt ###)

Now my setup is DSL and IPCop as my router. My guess is this is a NAT
Problem... but how do i get it fixed?
How can i extend the time period? maybe Asterisk just needs longer?

thanks for any help for this frustrated beginner! :)

Christian