[asterisk-bugs] [Asterisk 0014644]: Asterisk should transform SIP 503 code to SIP 500

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=14644 
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Reported By:                ibc
Assigned To:                mmichelson
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Project:                    Asterisk
Issue ID:                   14644
Category:                   Channels/chan_sip/Interoperability
Reproducibility:            always
Severity:                   major
Priority:                   normal
Status:                     assigned
Asterisk Version:           1.4.23 
Regression:                 No 
SVN Branch (only for SVN checkouts, not tarball releases): N/A 
SVN Revision (number only!):  
Request Review:              
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Date Submitted:             2009-03-11 11:08 CDT
Last Modified:              2009-03-14 09:31 CDT
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Summary:                    Asterisk should transform SIP 503 code to SIP 500
Description: 
Hi, in the following simple dialplan:

  exten => _X.,1,Dial(SIP/trunk1/${EXTEN})
  exten => _X.,n,Hangup

In case the trunk1 replies "SIP/2.0 503 Service Unavailable" Asterisk uses
the same SIP code to reply upstream. Asterisk shouldn't do it and MUST
convert that 503 into 500.

503 means that a client receiving it should try the same request against
an alternate server (got via DNS SRV and so).

This is "clearly" defined is RFC 3261:

-----------------------
21.5.4 503 Service Unavailable
   [...]
   A client (proxy or UAC) receiving a 503 (Service Unavailable) SHOULD
   attempt to forward the request to an alternate server.  It SHOULD NOT
   forward any other requests to that server for the duration specified
   in the Retry-After header field, if present.
-----------------------

Since Asterisk keep the 503 and replies it to the client, Asterisk breaks
the SIP failover mechanism, since it forces a client to contact an
alternate server when it's not needed at all (Asterisk is still alive and
working).

The correct behaviour is easy: When Asterisk receives a 503 from leg_B it
must convert it to 500 in leg_A.
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Relationships       ID      Summary
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related to          0014653 Never reply 503, use 500 instead (don't...
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---------------------------------------------------------------------- 
 (0101771) amilcar (reporter) - 2009-03-14 09:31
 http://bugs.digium.com/view.php?id=14644#c101771 
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About why 480 instead of 503 or 500:

Both 500 (Server Internal Error) or 503 (Service Unavailable) are relative
to SERVER status, and not destination status. Returning that code to the
pri causes above is incorrect.

DESTINATION status, like in this particular case, are handled with 404
(Not Found), 413 (Request Entity Too Large), 480 (Temporarily Unavailable),
486 (Busy Here), 600 (Busy), or 603 (Decline). 

Issue History 
Date Modified    Username       Field                    Change               
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2009-03-14 09:31 amilcar        Note Added: 0101771                          
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