How can i make Asterisk send keep alives to SIP Provider?

My asterisk box register in sip provider some accounts.
For outgoing calls all work fine, but if i stay some minutes with out use of sip provider, i stop to receive incoming calls because my gateway do not have a connectuin on nat table. So, how i setup asterisk to send keep alives for registered numbers on other provider ??

Thanks.

Fred

in sip.conf for voip provider, set
qualify=yes
this will periodically send a sip message to the provider and keep things working

if you are behind a NAT firewall you can also try forwarding port 5060 to your * box…

Thanks a lot.
After this change i can see keep alive send every 60s.

Thanks.