[asterisk-users] Caching Asterisk SIP useragent info?

[veselin at campbell-lange.net]

Hello,
I'm running an Asterisk 1.4.14 on a linux machine.
Serving SIP Snom users.

I've noticed that each time Asterisk is restarted, for the first 5-10
minutes, the SIP users can dial but cannot be dialed until each phone
re-registers itself against the server.

So only after the "Saved useragent...for peer 111" line appears on the
Asterisk console, then the 111 user can be reached. 

What exactly is this process?

Is it that the phones send their extension/password details to the
server at specific intervals or does the server send a broadcast
message, looking for phones?

Is there any way to cache/save this SIP useragent information so in case
the server is restarted, the user need not wait for their phone to
re-register?

Also I believe that it is sufficient for the user to just pickup their
handset in order to force their phone to re-register quicker.

However I'd like to avoid asking the users to do that.

Thank you much.

Veselin K