[Asterisk-Users] Application CallingPres

[Linus Surguy]

> On Wed, 2003-11-19 at 15:21, Olle E. Johansson wrote:
> > http://www.voip-info.org/tiki-index.php?page=Asterisk+cmd+CallingPres
> >
> > Could someone explain this applicatoin a bit more? I found the
application in the Zap channel source,
> > and a comment says something about PRI connections. What is the value
specifying?
>
> This CVS commit should help.
> http://lists.digium.com/pipermail/asterisk-cvs/2003-October/000205.html
>
> Call presentation is about whether or not callerid is displayed, what
> callerid is displayed, and similar.

The value itself is a means of giving information about the callers
telephone number. libpri incorrectly processes this as one value, where in
actual fact it is two different values, stored within the same byte.

The values itself is defined as follows in ITU Q931

Presentation indicator (octet 3a)
Bits
7 6 Meaning
0 0 Presentation allowed
0 1 Presentation restricted
1 0 Number not available due to interworking
1 1 Reserved

Screening indicator (octet 3a)
Bits
2 1 Meaning
0 0 User-provided, not screened
0 1 User-provided, verified and passed
1 0 User-provided, verified and failed
1 1 Network provided

In essence, it says 'is the person who has been called allowed to see the
callers number' and 'what authority was used to verify that this is a
genuine number'.

When I have a moment I'll look at contributing a tidyup of the handling of
this value as it is something that is important to us as a telco using
Asterisk in a carrier environment.

Linus