Time validity SIP authentication

Hello,

I have a client that sends a SIP REGISTER and refreshments to REGISTER.
My problem is that each refresh asterisk does not maintain the NONCE to avoid the 401 Unauthorized.
My question is which file I can change this parameter to NONCE or how to increase the validity of the authentication.

To better explain:
I have a client who asks for a sip registration with authentication parameter on asterisk
So the client sends a REGISTER, Asterisk responds 401 Unauthorized so the client returns a REGISTER (with user and password …] and asterisk responds with a 200OK so the client is registered at the time of asterisk.Mais refresh REGISTER asterisk reference yet 401 Unauthorized and I wish to avoid this every refresh but must register for one to do it.

Thank you,