[asterisk-users] Odd Busy tone on Aastra phones

[Steve Davies]

Hi,

I am curious to know whether anyone else can replicate my issue, or
can suggest an avenue of investigation. I have tried it with a number
of Aastra phones, and they all seem to do it (all SIP firmware 1.4.0).

If the SIP call takes the form:
  INVITE -> TRYING -> BUSY HERE
then everything seems to work fine. The phone makes the right busy
noises. On the other hand, if the SIP call takes the form:
  INVITE -> TRYING -> PROGRESSING -> BUSY HERE
then I get a very brief "blip" noise from the phone, and then silence
instead of a busy tone.

The first case is caused by having no Zap channels available. The
second case is caused by having a channel available, but where the
remote phone is actually busy.

Any clues would be most welcome. I cannot downgrade to SIP 1.3.x as
that has a bug with unattended transfers sometimes hanging up callers
:-(

Kind regards,
Steve