Technically, SDP in any 18x only serves to indicate where media should
be *sent*, and has nothing to do with whether you should receive media,
play received media, etc.
Nor does receiving a 180 mean you should play local ringback. It merely
says "the other end is being alerted". Nor does receiving a 183 after
receiving a 183 after a 180 mean you should *not* play local ringback.
If you have received a 180, you may want to play something indicating
the called device is alerting. If you are receiving media that you are
willing to render, you might want to do so in lieu of locally generated
ringback.
Unless you use ICE or SRTP, SIP doesn't really specify any way to
determine if media you are receiving is media the callee intended for
you to receive, rather than spam. As a result, some implementations
refuse to render received media unless it comes from the address they
are to send media to (symmetric RTP). You can do that if you feel you
must, but recognize that you may miss valid media from some implementations.
There is no perfect answer here. You can do pretty much as you wish.
(E.g. you aren't *required* to render any of the media you receive, even
after the call is established.) But you can also have a crappy
implementation that doesn't interoperate well with others if you make
unreasonable assumptions.
Thanks,
Paul
Kanumuri, Sreeram wrote:
> Nitin,
>
>> I checked the TO tag for both 18x and noticed that both are the same.
>> Do you think, that after sending 180 ringing(where local ringing should
>> generate), if my UAS is sending 183 without SDP will stop the local ringing?
>
> This is up to the implementation whether to play ringing (or) not.
>
> In this case, I feel you should stop the ringing after receiving 183 and show
> a different treatment to the originating UA (something like click,,click..)
> to indicate that the call is in progress...
>
>
> HTH,
> Sreeram.
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