[asterisk-users] How to check if a SIP phone isforwardedwithout ringing it ?

[Raj Jain]

Olle,

Yes, OPTIONS is too heavy for keep-alives and conflicts with its intended
usage - capability discovery without actually placing a call. The IETF seems
to be finally reaching a conclusion on how to do keep-alives in a
lightweight fashion. These are described in the SIP-outbound draft:

http://www.ietf.org/internet-drafts/draft-ietf-sip-outbound-11.txt

Basically, the idea is to use STUN for SIP/UDP and a CRLF packet for
SIP/TCP.

--
Raj


> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com 
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of 
> Johansson Olle E
> Sent: Wednesday, January 09, 2008 1:50 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [asterisk-users] How to check if a SIP phone 
> isforwardedwithout ringing it ?
> 
> 
> 9 jan 2008 kl. 02.48 skrev Raj Jain:
> 
> > This issue of phone vendors not supporting OPTIONS according to RFC
> > 3261
> > often comes up on this list. Like Kevin Fleming said, an OPTIONS 
> > request is supposed to be responded in the same way as an INVITE. 
> > Almost all SIP phone vendors have construed OPTIONS as some 
> kind of a 
> > keep-alive request, which is wrong.
> Which we do too, by the way. In worst case, maybe Asterisk 
> has set this industry standard.
> 
> OPTIONS is far to heavy in processing on the server side to 
> be used for keep-alives. I'm  starting to see devices that 
> use it for checking capabilities - the proper way. To do this 
> properly, we will have to authenticate the OPTIONs request 
> and match it with the proper peer/ user to get the proper 
> codec settings, ACLs and such.
> 
> Since all versions of Asterisk use OPTIONs for 
> NAT-keepalives, I'm a bit hesitant to fix this. It's a catch 
> 22. I want to do it properly, but then the amount of 
> processing for each OPTIONs request that we receive is going 
> to be a bit too much. Maybe one could ask vendors to add a 
> header to the  OPTIONs packet saying "this is just a keep-alive.  
> Give me a 200 OK without any parsing and be happy, because I 
> don't care about the reply."
> 
> Linksys has a setting and use NOTIFY for Keep-alives, which 
> also is a poor solution, but at least something we can just 
> give an error response to without a lot of processing. There 
> was a proposal for PING, but it never got anywhere.
> 
> /O
> 
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