Asterisk fails to Reregister

I have an server running Asterisk It is connected to a local SIP provider for telephone service. It re-registers correctly 98% of the time, but every couple of days it will fail to re-register, which clause our phones to go down for 5 to 10 min before it is able to register again. all calls finish but new calls cant be made or received. I have tcpdump running and i can see where Asterisk send the request to register every hr except for when it dose not work. So for some reason Asterisk is not sending the request every couple of days at any given time. Any help is appreciated.

Try to user lower register-expire settings for the sip clients. Also check you bandwith whether it is creating issues at certain periods or not? another way is to use qualify=yes setting so sip client get refereshed at a regular interval.

Am I understanding correct that the phones are not registering or your trunk to the service provider.

If phones check the firmware. I had an issue with Snom 320, where when phone memory got full, it would deregister causing the same issue. Wrote a script to reboot phones once a week to clear ram untill Snom released new firmware that resolved the issue.