[asterisk-bugs] [Asterisk 0017071]: When using another SIP Trunk, Asterisk generates the initial ring RING as a response to "SIP SESSION PROGRESS"

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=17071 
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Reported By:                Alex Oniciuc
Assigned To:                
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Project:                    Asterisk
Issue ID:                   17071
Category:                   Channels/chan_sip/General
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     confirmed
Asterisk Version:           SVN 
JIRA:                       SWP-1137 
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases):  trunk 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2010-03-22 05:43 CDT
Last Modified:              2010-03-24 14:18 CDT
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Summary:                    When using another SIP Trunk, Asterisk generates the
initial ring RING as a response to "SIP SESSION PROGRESS"
Description: 
I’m having a strange problem with the VoIP Gateway that I’m using to go
on the PSTN: if the number on the other end is busy or unavailable I hear
an initial RING, generated by Asterisk from what I’m seeing and after
that the line goes down with busy signal:

Here is the scenario:

    Softphone    *ASTERISK                PATTON                   PSTN
[BUSY]

1   INVITE     >  INVITE              >   INVITE
2.	                              <   SIP/2.0 100 Trying
3.  RING      <  SIP/2.0 180 Ringing  <   SIP/2.0 183 Session Progress
4.	      <  SIP/2.0 603 Declined <   SIP/2.0 406 Not Acceptable

Is this regular? Asterisk isn’t supposed to generate the RING  only
after the first one received from the PATTON?

This can be very annoying because the calling party may have the
impression that the remote party hang up.
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 (0119852) ebroad (manager) - 2010-03-24 14:18
 https://issues.asterisk.org/view.php?id=17071#c119852 
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People expect IP PBX's to work like a traditional PSTN based PBX, in most
respects. We(humans) distinguish line state based on audible tones, i.e.
ringing, busy, disconnected etc. When a gateway/PBX in an IP based system
sends a caller call progress information without any way of establishing a
media path in order for the person on the line to determine the line
state(and the PBX for that matter), then the calling PBX, in this case,
Asterisk, needs to make assumptions, which is a very slippery slope;
basically damned if you, damned if you don't. 

Issue History 
Date Modified    Username       Field                    Change               
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2010-03-24 14:18 ebroad         Note Added: 0119852                          
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