asterisk/UPGRADE.txt

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===
=== Information for upgrading between Asterisk 1.6 versions
===
=== These files document all the changes that MUST be taken
=== into account when upgrading between the Asterisk
=== versions listed below. These changes may require that
=== you modify your configuration files, dialplan or (in
=== some cases) source code if you have your own Asterisk
=== modules or patches. These files also includes advance
=== notice of any functionality that has been marked as
=== 'deprecated' and may be removed in a future release,
=== along with the suggested replacement functionality.
===
=== UPGRADE-1.2.txt -- Upgrade info for 1.0 to 1.2
=== UPGRADE-1.4.txt -- Upgrade info for 1.2 to 1.4
=== UPGRADE-1.6.txt -- Upgrade info for 1.4 to 1.6
===
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As of 1.6.0.16:

* The firmware for the IAXy has been removed from Asterisk.  It can be
  downloaded from http://downloads.digium.com/pub/iaxy/.  To have Asterisk
  install the firmware into its proper location, place the firmware in the
  contrib/firmware/iax/ directory in the Asterisk source tree before running
  "make install".

* T.38 FAX error correction mode can no longer be configured in udptl.conf;
  instead, it is configured on a per-peer (or global) basis in sip.conf, with
  the same default as was present in udptl.conf.sample.

* T.38 FAX maximum datagram size can no longer be configured in updtl.conf;
  instead, it is either supplied by the application servicing the T.38 channel
  (for a FAX send or receive) or calculated from the bridged endpoint's
  maximum datagram size (for a T.38 FAX passthrough call). In addition, sip.conf
  allows for overriding the value supplied by a remote endpoint, which is useful
  when T.38 connections are made to gateways that supply incorrectly-calculated
  maximum datagram sizes.

As of 1.6.0.15:

* There have been some changes to the IAX2 protocol to address the security
  concerns documented in the security advisory AST-2009-006.  Please see the
  IAX2 security document, doc/IAX2-security.pdf, for information regarding
  backwards compatibility with versions of Asterisk that do not contain these
  changes to IAX2.

From 1.6.0.10 to 1.6.0.11:

* 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.

From 1.6.0.9 to 1.6.0.10:

* Support for Taiwanese was incorrectly supported with the "tw" language code.
  In reality, the "tw" language code is reserved for the Twi language, native
  to Ghana.  If you were previously using the "tw" language code, you should
  switch to using either "zh" (for Mandarin Chinese) or "zh_TW" for Taiwan
  specific localizations.  Additionally, "mx" should be changed to "es_MX",
  Georgian was incorrectly specified as "ge" but should be "ka", and Czech is
  "cs", not "cz".

From 1.6.0.1 to 1.6.0.2:

* The ast_agi_register_multiple() and ast_agi_unregister_multiple()
  API calls were added in 1.6.0, so that modules that provide multiple
  AGI commands could register/unregister them all with a single
  step. However, these API calls were not implemented properly, and did
  not allow the caller to know whether registration or unregistration
  succeeded or failed. They have been redefined to now return success
  or failure, but this means any code using these functions will need
  be recompiled after upgrading to a version of Asterisk containing
  these changes. In addition, the source code using these functions
  should be reviewed to ensure it can properly react to failure
  of registration or unregistration of its API commands.

* The ast_agi_fdprintf() API call has been renamed to ast_agi_send()
  to better match what it really does, and the argument order has been
  changed to be consistent with other API calls that perform similar
  operations.