Merged revisions 208464 via svnmerge from

https://origsvn.digium.com/svn/asterisk/trunk

........
  r208464 | kpfleming | 2009-07-23 16:57:24 -0500 (Thu, 23 Jul 2009) | 46 lines
  
  Rework of T.38 negotiation and UDPTL API to address interoperability problems
  
  Over the past couple of months, a number of issues with Asterisk
  negotiating (and successfully completing) T.38 sessions with various
  endpoints have been found. This patch attempts to address many of
  them, primarily focused around ensuring that the endpoints'
  MaxDatagram size is honored, and in addition by ensuring that T.38
  session parameter negotiation is performed correctly according to the
  ITU T.38 Recommendation.
  
  The major changes here are:
  
  1) T.38 applications in Asterisk (app_fax) only generate/receive IFP
  packets, they do not ever work with UDPTL packets. As a result of
  this, they cannot be allowed to generate packets that would overflow
  the other endpoints' MaxDatagram size after the UDPTL stack adds any
  error correction information. With this patch, the application is told
  the maximum *IFP* size it can generate, based on a calculation using
  the far end MaxDatagram size and the active error correction mode on
  the T.38 session. The same is true for sending *our* MaxDatagram size
  to the remote endpoint; it is computed from the value that the
  application says it can accept (for a single IFP packet) combined with
  the active error correction mode.
  
  2) All treatment of T.38 session parameters as 'capabilities' in
  chan_sip has been removed; these parameters are not at all like
  audio/video stream capabilities. There are strict rules to follow for
  computing an answer to a T.38 offer, and chan_sip now follows those
  rules, using the desired parameters from the application (or channel)
  that wants to accept the T.38 negotiation.
  
  3) chan_sip now stores and forwards ast_control_t38_parameters
  structures for tracking 'our' and 'their' T.38 session parameters;
  this greatly simplifies negotiation, especially for pass-through
  calls.
  
  4) Since T.38 negotiation without specifying parameters or receiving
  the final negotiated parameters is not very worthwhile, the
  AST_CONTROL_T38 control frame has been removed. A note has been added
  to UPGRADE.txt about this removal, since any out-of-tree applications
  that use it will no longer function properly until they are upgraded
  to use AST_CONTROL_T38_PARAMETERS.
  
  Review: https://reviewboard.asterisk.org/r/310/
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git-svn-id: http://svn.digium.com/svn/asterisk/branches/1.6.2@208501 f38db490-d61c-443f-a65b-d21fe96a405b

1 files changed, 10 insertions, 0 deletions

diff --git a/UPGRADE.txt b/UPGRADE.txt
index be34c0412..238920ceb 100644
--- a/UPGRADE.txt
+++ b/UPGRADE.txt
@@ -20,6 +20,16 @@
 
 From 1.6.1 to 1.6.2:
 
+* Beginning with this release, Asterisk's internal methods of
+  negotiating T.38 (FAX over IP) sessions changed in
+  non-backwards-compatible ways. Any applications that previously used
+  AST_CONTROL_T38 control frames will have to be upgraded to use
+  AST_CONTROL_T38_PARAMETERS control frames instead; app_fax.c is a good
+  example of how to generate and respond to these frames. These changes
+  were made to solve significant T.38 interoperability problems between
+  Asterisk and various SIP/T.38 endpoints identified by many users of
+  Asterisk.
+
 * The default console now will use colors according to the default background
   color, instead of forcing the background color to black.  If you are using a
   light colored background for your console, you may wish to use the option