[asterisk-users] Outbound call: caller gets no ringback on session progress

Michael Maier m1278468 at mailbox.org
Tue Jan 22 11:14:53 CST 2019

On 17.12.18 at 11:52 Joshua C. Colp wrote:
> On Sun, Dec 16, 2018, at 4:43 AM, Michael Maier wrote:
> <snip>
>> Another question: is there any use case for 183 Session Progress w/o 
>> SDP? IOW: Is a 183 Session
>> Progress just a bug of the ISP? If so, problem could be solved by 
>> dropping each 183 package w/o SDP.
> Nothing really comes to mind that would be accomplished by sending a 183 without SDP but there may be cases on the internet.

As long as [1] aren't fixed, the attached patch could be used as workaround. This workaround drops 183 Session Progress w/o SDP.

The attached workaround assumes, that 183 Session Progress w/o SDP is followed by 180 Ringing. If there isn't any 180 Ringing following, this patch won't fix anything. In
the latter case, it would be necessary to generate inband ringing by asterisk or send 180 Ringing instead of the broken 183 Session Progress.

The workaround applies to 13.24.1.

Caller		Asterisk				ISP
Invite -------->
			<-----------------------	183 Session Progress w/o SDP
			<-----------------------	180 Ringing
<---------------180 Ringing

Another 183 Situation with *P-Early-Media* header

Caller		Asterisk			ISP
Invite -------->
		    <--------------------------		183 Session Progress w SDP / P-Early-Media:sendonly
<-------------	183 Session Progress w SDP sendrecv
<-------------  RTP
--------------> RTP
		    <--------------------------		180 Session Progress w/o SDP / P-Early-Media:sendonly
		    <--------------------------		RTP (inband ringback)

=> the sendonly-value of P-Early-Media seems to be ignored. Asterisk doesn't apply the sendonly value of the P-Early-Media header of the 183 Session Progress package
received from the ISP to the 183 Session Progress sent to the caller.
But this is not a problem, as the ringback can still be transferred.


[1] https://issues.asterisk.org/jira/browse/ASTERISK-28208, https://issues.asterisk.org/jira/browse/ASTERISK-27994
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