IMO the behavior of OPTIONS - where it is expected to return the same
result as an INVITE would - was short sighted. It is biased toward
INVITE, in that it can't say what a SUBSCRIBE or PUBLISH or MESSAGE
would respond. As you say, probably many UAs don't support this.
Presence is a better way to determine the DND status of a callee.
Paul
Iñaki Baz Castillo wrote:
> If a UAS is in DND mode (DontDisturb) it will reply "480" (or 486/603) for an
> incoming INVITE.
>
> Of course sending an INVITE is not a valid way to know the UAS status since
> INVITE will make ring the phone, create a "missed call" in phone GUI and so.
>
> Theorically if an UAS in DND mode receives a OPTIONS it should reply with the
> same as in case of INVITE, so sending an OPTIONS would be valid to know the
> status of the UAS:
>
> 11.2 Processing of OPTIONS Request
>
> The response to an OPTIONS is constructed using the standard rules
> for a SIP response as discussed in Section 8.2.6. The response code
> chosen MUST be the same that would have been chosen had the request
> been an INVITE. That is, a 200 (OK) would be returned if the UAS is
> ready to accept a call, a 486 (Busy Here) would be returned if the
> UAS is busy, etc. This allows an OPTIONS request to be used to
> determine the basic state of a UAS, which can be an indication of
> whether the UAS will accept an INVITE request.
>
> Unfortunatelly just a few SIP devices implement this behaviour:
>
> - Thomson S2030 always reply 200.
> - Linksys seems to do the same.
>
> Is it really extended? I'm doing a script to check the status of phones so I
> need OPTIONS working with the real status of phones (this is, receiving the
> same reply as it the request is an INVITE).
>
> Thanks for any comment.
>
>
>
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