I would guess that is a keep alive. 
Are you connection to sipauth.deltathree.com?
Zac
On Fri, 2004-04-30 at 13:34, Sathya wrote:
> Hello,
>  
> Recently I am seeing this message on my asterisk console received
> from Iconnect. 
>  
> Apr 30 11:37:21 NOTICE[1125329600]: chan_sip.c:5648 handle_request:
> Unknown SIP command 'NOTIFY' from '213.137.73.41'
> It is prety annoying as it appears once every four seconds.
>  
> I've seen similar posts in the archives which points me to NAT keep
> alives being send by the remote end. I am actually on public internet
> and there is no NAT involved in, hence no nat config in sip.conf.
>  
> Why would iconnect send notify messages ? Is there a config setting
> that I could make so that this message not being sent to me. 
> Cheers
>  
> SW
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