[asterisk-dev] Potentially naughty patch

[Tilghman Lesher]

On Tue, Oct 29, 2013 at 10:43 AM, Olle E. Johansson <oej at edvina.net> wrote:
>
> On 29 Oct 2013, at 15:33, Tilghman Lesher <tilghman at meg.abyt.es> wrote:
>
>> On Tue, Oct 29, 2013 at 4:01 AM, Olle E. Johansson <oej at edvina.net> wrote:
>>> 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.
>
> Noted.
>
> Eventually I want a core that is not based on ISDN anymore. But that's another story.

Speaking historically, we could just have easily chosen SIP cause
codes as the internal representation.  Or we could have made up our
own.  For that matter, if the issue is backwards compatibility to
ISDN, then using values in the 128+ range would make sense, possibly
enjoining the ISDN driver from sending those codes directly.  Assuming
that you wouldn't want to ever send a SIP cause code lower than 128,
using the SIP cause code directly in this field (it is, after all, a
full integer) may be preferable.  If you would need to send lower
values, however, then multiplying the SIP cause code by a certain
factor (say 1,000) may be sufficient.  Changes would need to be made,
though, to ensure that other areas of Asterisk do not assume that the
value will fit within a single 8-bit field.

-Tilghman