[asterisk-bugs] [Asterisk 0017849]: Asterisk does not properly align SDP "m=" lines when answering an SDP offer (provoking a T.38 negociation issue)

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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https://issues.asterisk.org/view.php?id=17849 
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Reported By:                frawd
Assigned To:                
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Project:                    Asterisk
Issue ID:                   17849
Category:                   Channels/chan_sip/General
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     acknowledged
Asterisk Version:           SVN 
JIRA:                        
Regression:                 No 
Reviewboard Link:            
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2010-08-12 10:23 CDT
Last Modified:              2010-08-13 10:14 CDT
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Summary:                    Asterisk does not properly align SDP "m=" lines when
answering an SDP offer (provoking a T.38 negociation issue)
Description: 
It appears that Asterisk generates SDP replies with "m=" lines always
aligned in the same order:
1. m=audio
2. m=video
3. m=text
4. m=image

When it should reply with the same order that was in the initial offer per
RFC-3264 (page 8):

[QUOTE]For each "m=" line in the offer, there MUST be a corresponding "m="
line in the answer. The answer MUST contain exactly the same number of "m="
lines as the offer. This allows for streams to be matched up based on their
order. This implies that if the offer contained zero "m=" lines, the answer
MUST contain zero "m=" lines.[/QUOTE]

This could potentially provoke many interoperability issues, one of which
is presented below.
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 (0125942) ebroad (manager) - 2010-08-13 10:14
 https://issues.asterisk.org/view.php?id=17849#c125942 
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Unfortunately there isn't much that is copied between the originating
request and the outbound request from Asterisk, another good example of
this is fmtp values for video. From what I understand of the code, passing
information like this between two sip_pvt structs is going to require some
serious work. 

Issue History 
Date Modified    Username       Field                    Change               
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2010-08-13 10:14 ebroad         Note Added: 0125942                          
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