[Serusers] Registration exporation

[Decebal Topala]

Hello There 

I haver run into a issue.
After running ser for 1 hour all the phones cannot call reach other and
ip phones are not reachable from pstn gateway any more.
I assume this is due to the registration expiration. 
Is there any way to reinforce (force Reregister call ) from ser to the
UA so they do not become unavailable.  I understand that i can
increase the expiration time from 60 to 45 days but i don't think it
is good idea.
Thanks.
Appreciate any help.
Decebal