[asterisk-users] destroying time

[nakaji]

Hello,

Please forgive me if I'm repeating this post.
I have searched and looked for similar question but have not seen a similar 
one.

When I do call from client to Asterisk 1.8,

I do follows.

1. REGISTER
2. INVITE
3. call established
4. Bye
5. call ended

After the call ended, my client receive the message like this.

"Really destroying SIP dialog '54c09c884a61e39140a2358a5adb7d96 at 192.168.1.2' 
Method: REGISTER"


And at least after 30sec, my client disconnect from Asterisk.
I have to do REGISTER again.

I think this message means that "Asterisk will delete registration".

Is this right ?

And why the time is about 30 sec ?
Is this default time ?
How to change tihis time ?


any help appreciated.

nakaji