[asterisk-dev] Re: why 'o' (preserve original callerid) is not default in app_dial.c ?

[Luigi Rizzo]

On Wed, Nov 01, 2006 at 10:06:54AM +0000, Tony Mountifield wrote:
> In article <45481689.9050304 at digium.com>,
> Russell Bryant <russell at digium.com> wrote:
> > Luigi Rizzo wrote:
> > > For first, i do not understand the reason for setting
> > > the callerid in the ast_channel to the one of the _called_ extension;
> > > the information is already in cid_rdnis.
> > > On the other hand, if 'o' is not the default, there must be a
> > > good reason, and this must be the most useful case ?
> > 
> > Previously, the CallerID information from the calling channel was copied to the 
> > called channel.  This is no longer the default behavior, but is available 
> > through the use of the 'o' option.
> > 
> > Now, the default CallerID number for the called channel is that of the extension 
> > that was called.  This may not be the best thing, but it is certainly more 
> > correct than the CallerID of the calling channel.  RDNIS will not always be set, 
> > so we can't rely on that.  However, it may be an even better choice than the 
> > called extension when it is available.
> > 
> > That was at least the reasoning when these changes occurred ...
> > 
> > > But what is really confusing to me is that this change occurs after the
> > > invocation of ast_call(), which means that the manager events
> > > will report different information from what you see eg in the channel
> > > driver when it responds to the ast_call (and possibly stores the
> > > state from the channel itself).
> > 
> > This sounds like it could be a bug to me.  I would think processing this option 
> > would come after the call to ast_request(), but before ast_call().  However, I 
> > have a feeling that not many people use the 'o' option, so that could be why it 
> > was never reported.
> 
> I don't think it is a bug. It took me a while to understand the reasoning
> behind these changes, but I think I did in the end:
> 
> a) When making a call using Dial, the caller-ID from the incoming channel
> is still copied to the outgoing channel (i.e. between ast_request() and
> ast_dial()), so that when the destination phone rings, it correctly displays
> the phone number of the original caller. This has always been the case since

right, and this is the intuitive part.

> before the 'o' option was introduced. If the processing of the "not-'o'" was
> moved to before ast_call(), the called party's phone would show their own
> number when the phone was ringing, which would be a bit daft!
> 
> b) Once the call has been answered, the called channel is just another
> channel in Asterisk. The new behaviour, which is inhibited by the 'o'
> options, is at that point to change the channel's caller-ID to be that

aha, but the problem is that the info is overwritten even before the
call is answered. E.g. if you issue the 'status' command from a manager
connection, you will see the channel as Ring(ing?) and with the callerid
reflecting the destination, not the source - that's without 'o', of course.

> of the called device. The reasoning, I believe, is that then every
> answered channel's caller-ID will reflect the extension that is on that
> channel.  This may be even more important if the called channel is then
> put into the dialplan using Redirect (ast_async_goto) and could place calls
> of its own.
> 
> So I think the current behaviour is correct and well thought out. What
> is probably missing is somewhere within the source tree that the rationale
> behind such decisions could be recorded when they are made, especially if
> they are counter-intuitive at first glance.

I think (and the comments on this thread convince me even more)
that the root of the problem is that we have one slot in the channel
descriptor (callerid) to represent at least two (possibly more if
we want to record the "routing" of the call) pieces of information:
the source and the destination.

Until we make these two separate entries, there will always be confusion
on what information is there - as you show, sometimes you need the
source (e.g. when presenting 'who is calling me?' info to the destination),
sometimes you need the destination (e.g. when rerouting, or deciding
which voice-mailbox to use, etc.)

	cheers
	luigi

> Cheers
> Tony
> -- 
> Tony Mountifield
> Work: tony at softins.co.uk - http://www.softins.co.uk
> Play: tony at mountifield.org - http://tony.mountifield.org
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