100 Message received
100 Looking up number
100 Found number, looking up carrier according to profile
100 Finding cheapest carrier which doesn't do animal testing
100 Found carrier "AT&T"
100 Dialing number
180 Ringing
182 Queued, 3 people in front of you
182 Queued, 2 people in front of you

The language of the status message should be determined based on the Accept-Language request header in the call.

A 183 (Session Progress) status response will appear in RFC2543bis. It can be used for both progress tones as well as error messages.

One would use the 183 only if you:

• Are able to determine that the audio being generated is something other than ringing (e.g. "comfort tone" or "pay tone" as defined in E.18x), or
• Are unable to definitively determine that alerting is occuring. This really should only happen with older CAS protocols. ISUP and ISDN have sufficient information to determine what is happening on the far end.

One can also use 183 if the gateway is able to determine that an error has occured, but that there is a tone or announcement accompanying it (e.g., an ACM with a cause code present). In that case, the gateway can send a 183 to set up the media for the announcement (ideally with the announcement text as the text string), wait for a timer (on the order of 30 seconds), and then send an appropriate SIP error message.

However, this should only be done if the caller is likely a human being, as sending 183 would otherwise only delay failure handling.

Take a look at (now expired) draft-ietf-sip-183-00.txt for some details on using 183 responses for early media announcements.
2000-Jul-03 7:23pm islepchin@dynamicsoft.com