[SIPForum-discussion] Difference between sip180 and sip183.

[Paul Kyzivat]

On 8/16/15 6:02 PM, Rafael Diego Farias de Oliveira wrote:
> Hello,
> What is the sip180 and sip183 and what problems may occur due to these
> parameters.
> I know sip180 is ringing and the 183 is the session progress and he
> carries the sdp.
> I am with this question because I do not know that troubleshooting
> should do in order to identify problems regarding these parameters.

*Any* 18x response can carry SDP. The only real difference between 183 
and 180 is that 180 *also* indicates that the callee is alerting. From 
an offer/answer perspective they are identical.

The UAC should use both the availability of SDP from the callee and the 
contents of the resulting media stream, along with the 180 indication of 
alerting if it has been received, to decide how to alert locally. 
Generally, if you are receiving in-band media you should play that out. 
If not, then if you have received a 180 then you should generate local 
ringback.

You must not assume that 180 and 183, with or without SDP, will arrive 
in some particular order.

	Thanks,
	Paul