Manoj Priyankara [TG] wrote:
> Hi Paul,
> Thanks! Hope you are doing well!
>
> This is not to check whether a particular dialog is alive. But to check
> whether the UAS is alive. This might be useful when a particular UAC
> such as an IAD wants to know the liveness of the UAS.
>
> I've seen some SIP ALG's use this method to see the availability of the UAS.
Its reasonable for checking general availability of the UA, assuming of
course that you know the URI of the UA, rather than just of the AOR.
Thanks,
Paul
> BR,
> Manoj
>
>
> -----Original Message-----
> From: Paul Kyzivat [mailto:pkyzi...@cisco.com]
> Sent: Sun 8/9/2009 2:48 AM
> To: Manoj Priyankara [TG]
> Cc: sip-implementors@lists.cs.columbia.edu
> Subject: Re: [Sip-implementors] SIP OPTIONS
>
>
>
> Manoj Priyankara [TG] wrote:
> > Dear All,
> >
> > According to the RFC 3261, SIP OPRIONS message should be used to query
> > the statue of other UAC or the UAS. Is it OK to use the OPTIONS as a
> > keep alive message to know whether the UAS is alive?
> >
> > Is it necessary to send the OPTIONS message from a registered user or is
> > it possible to send the OPTIONS message from a general user and get 200-
> > OK as the response?
>
> Its not entirely clear what you want to determine by using OPTIONS.
>
> Are you looking to verify the liveness of your peer UA in a dialog?
> If not, what?
>
> OPTIONS isn't a good choice for testing the peer in a dialog.
> If you send it in-dialog (using the remote target, route set, call ID,
> from and to tags of the dialog), then presumably it will follow the path
> of dialog. But when it reaches the UAS, according to 3261 it is supposed
> to treat the same as an OPTIONS received out of dialog. Its not entirely
> clear what that means. It might mean that it could succeed even though
> the UA has lost track of the dialog. (Consider for instance that the UA
> has rebooted and lost all state.)
>
> Because the handling is somewhat ambiguous in this case, you can't trust
> the results to report what you want to know.
>
> To test the liveness of your peer in an invite dialog you are better off
> to use reINVITE or UPDATE.
>
> Thanks,
> Paul
>
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