chan_dahdi: Add the chan_dahdi.conf force_restart_unavailable_chans option.

Some telco switches occasionally ignore ISDN RESTART requests.  The fix
for ASTERISK-19608 added an escape clause for B channels in the restarting
state if the telco ignores a RESTART request.  If the telco fails to
acknowledge the RESTART then Asterisk will assume the telco acknowledged
the RESTART on the second call attempt requesting the B channel by the
telco.  The escape clause is good for dealing with RESTART requests in
general but it does cause the next call for the restarting B channel to be
rejected if the telco insists the call must go on that B channel.

chan_dahdi doesn't really need to issue a RESTART request in response to
receiving a cause 44 (Requested channel not available) code.  Sending the
RESTART in such a situation is not required (nor prohibited) by the
standards.  I think chan_dahdi does this for historical reasons to deal
with buggy peers to get channels unstuck in a similar fashion as the
chan_dahdi.conf resetinterval option.

* Add the chan_dahdi.conf force_restart_unavailable_chans compatability
option that when disabled will prevent chan_dahdi from trying to RESTART
the channel in response to a cause 44 code.

ASTERISK-25034 #close
Reported by: Richard Mudgett

Change-Id: Ib8b17a438799920f4a2038826ff99a1884042f65

1 files changed, 3 insertions, 0 deletions

diff --git a/CHANGES b/CHANGES
index fcb4877f4..1b3961954 100644
--- a/CHANGES
+++ b/CHANGES
@@ -48,6 +48,9 @@ chan_dahdi
 ------------------
  * The CALLERID(ani2) value for incoming calls is now populated in featdmf
    signaling mode.  The information was previously discarded.
+ * Added the force_restart_unavailable_chans compatibility option.  When
+   enabled it causes Asterisk to restart the ISDN B channel if an outgoing
+   call receives cause 44 (Requested channel not available).
 
 chan_iax2
 ------------------