On 4/12/2011 12:21 PM, Randell Jesup wrote:
>> 3 apr 2011 kl. 13.23 skrev Iñaki Baz Castillo:
>>
>>> 2011/3/31 Olle E. Johansson<[email protected]>:
>>>> If you are sending only ringback, I would recommend sending 180 with SDP
>>>> instead of 183. If you're sending 183, I can't move my state machine to
>>>> ringing state, which would help a lot of 3rd party apps. If you send
>>>> ringback in 183 - they won't notice the ringing and would see the call
>>>> going from calling state directly to answer, which is confusing. Sending
>>>> ringback with 183 and not sending 180 is a problem for many apps.
>>>>
>>>> Use 183 only if you have an operator message to play. Otherwise, add SDP
>>>> to the 180 Ringing.
>>>
>>> Hi Olle. So you propose that ringback (just pure ringback with no
>>> voice announcement) should be always sent in a 180 response (with or
>>> without SDP, as usually SIP phones generate 180 with no SDP, of
>>> course).
>> Yes. I am not saying that you should always send ringback with 180, but
>> if you do want to send ringback in audio, use 180.
>
> I should tell you that this is opposite how almost all commercial
> products work; 180 is normally used without SDP for telling the caller
> to generate internal ringback, and 183 with SDP is used for providing
> remote ringback (usually from a SIP->PSTN gateway). Most UA devices
> don't send ringback themselves and just send 180 to the server.
>
>>> And just use 183 (always with SDP for sure) when the media contains an
>>> announcement ("the number you are calling is not available" and so).
>> exactly.
>>
>>> Am I right?
>> Yes.
>>
>> 183 doesn't say much about the state change, but 180 is actually a
>> state change indicating that something is alerting the target about an
>> incoming call. This is very important in gateway situations, like a
>> b2bua like Asterisk.
>
> A quote from this list from 2008 (use the archives!!!):
>
> RFC3960 gateway model gives guidelines about the, let's say, "correct"
> behavior. The main rule says more or less "media has always the
> precedence".
> About the scenario you mentioned in the text, i.e. 183/SDP and then 180
> (no
> SDP I assume) you should play a local ringback ONLY in the case you don't
> receive any media (despite the media channel has been established).
> In the reverse case, i.e. 180/noSDP and the 183/SDP the rule is the same,
> meaning you should play the media. Should the media missing, you would
> continue to play the local ringback due to the 180.
>
> This is what RFC3960 says. In the real world (especially when you
> interoperate to the PSTN) it doesn't work in some case. My
> recommendation is
> to always use the latest received message as the most significant. Then,
> in
> the first case once receiving the 180 I would suggest to play a local
> ringback stopping playing the media, in the second one to stop the local
> ringback and play the media (if any). Using this approach, I didn't find
> yet
> any failing case when interoperating with PSTN (this is the most complex
> scenario usually) in the operator's network I'm working with.
I don't understand. What is there about the "gateway" model that doesn't
work in the real world with the PSTN?
Thanks,
Paul
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