[Users] 180 Ringing / 183 Session Progress

[Atle Samuelsen]

Hi Sam,

* Sam Lee <sam.lee at super.net.sg> [070206 11:09]:
> Hey Guys,
>  
> Is it mandatory for SIP servers to generate to UA 180 Ringing to inform
> them that the called party is now ringing ?

No
>  
> The reason i'm asking is because I am seeing strange results using
> different UAs.
>  
> Using SIP clients to call out , instead of seeing 180 Ringing , i see
> 183 session progress even before call was picked up.

This is nothing wrong with this :)
>  
> On some sip client , ring back can be heard.
good, they support early media
> On some others , ring back cannot be heard.
Bad,, they do not support Early media
>  
> Is there any reason to suspect that these UAs needs to receive 180
> Ringing before generating any ringback ?
In general: 
180 == Generate Local Ringback.
183 == get RTP from callee, and play it (often used for network
announcements, calls to gSM and simular)

- Atle
>  
> Regards,
> Sam

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