[asterisk-dev] Potentially naughty patch

[Tilghman Lesher]

On Tue, Oct 29, 2013 at 4:01 AM, Olle E. Johansson <oej at edvina.net> wrote:
> I have a branch that makes it possible to add custom mappings to the isdn
> cause code to SIP codes table in chan_sip - and the opposite ones.
>
> In order to a fine grained control I may want a cause code to send a very
> specific SIP message, maybe even a custome one. And in some cases I want to
> translate a specific SIP code to the same without affecting other calls in
> sip2sip situations.
>
> My solution was to add five custom codes to the cause table - custom1 to
> custom5 in the range 115-119 that is not used as far as I can tell.
>
> This solved the problem we worked on and also added the benefit of being
> able to run "hangup(118)" on a SIP call to generate "498 IAX2 not supported"
> in the SIP channel.
>
> The questions are:
> - is this too dangerous, to grab some ISDN cause codes?
> - will it have side effects?
> - what will other channels do if they get a hangup(119) ?
>
> All of this is of course a bit dangerous and have to be used only by
> experienced asterisk admins, but is something that have been asked for for a
> long time. There is nothing stopping you from redefining any cause code to
> 401, 180 or something else, like 302. But that will hurt...

The only thing I fear from such a change is that it will lead to a
support nightmare if any of the cause codes that you've appropriated
are eventually used in another way by the ITU.  Since that's the
standards body involved with the definition of ISDN, I'd suggest that
you obtain from them an assurance that such cause codes land in a
"reserved" or "vendor-defined" state, to avoid this potential
future-compatibility issue.  It also creates a potential future issue
within Asterisk, whereby if the lowest cause code is allocated, and
that custom code needs to be moved, then there will be an issue with
"custom1" being assigned to a different integer on two different
versions of Asterisk.  This only potentially matters when the cause
code is transmitted externally, as we might in the ISDN driver.