[SIPForum-discussion] discussion Digest, Vol 38, Issue 23

[Stephen James]

Since 183 does not indicate alerting, only progress, such as "I'm working on it" no ringback should be provided.

>   1. 183 no sdp and ringback tone (Anthony Orlando)
> I have a question regarding ringtone and 183 without SDP.  We have a call from SIP to ISDN BRI.  Both channels are busy, but the ISDN gw sends 183 > while trying the two b channels.  This is causing the SIP phone to play ringback tone to the caller.  Then the ISDN GW sends a 486 and then we get the > busy tone.  Of course this is unwanted behavior.  I can't find any reference that says a UA should provide or not provide ringback tone with a 183.  >Anyone care to enlighten me?

Anthony
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