[Asterisk-Users] Q: How to get the preset callerid from a CLID-no-screen E1-PRI

[Peter Svensson]

On Sat, 5 Feb 2005, Frank Sautter wrote:

> > What network do you receive this from? 
> the calling party has an E1-PRI from the "Deutsche Telekom" (germany's 
> former monopolist) and our E1-PRI is from "Arcor" which is on of the new 
> telco companies founded after the liberation of the telco market in germany.
> as mentioned on my first email, they have enabled the ISDN feature 
> CLIP-no screening.... but from the debug it seems, as if a screened 
> number is sent after the unscreened number.
> but this is not the only caller i noticed this behaviour. a bank in our 
> town also shows this behaviour (but arranging a call from them is not so 
> easy).
> 
> > Neither ITU q.931 nor ETSI EN 300 403-1 (EiroISDN definition) lists the "Calling 
> > Number" IE among those that may be repeated. 
> but it seems as if this behaviour is 'normal' because on every telephone 
> line i tested this, the number shown is the unscreened number which came 
> first in the debug

Ok, I got interested and dug a bit deeper. In the Deutsch Telekom 
implementation specification for EuroISDN ("1 TR 67", available at 
http://www.telekom.de/dtag/downloads/1/1TR67-V1.0.pdf) in the reference to 
clause 4.5.1.1 from ETS 300 102-1 the calling party number is allowed to 
be present up to two times. 

The behaviour you are seeing is described by ETSI ETS 300 092-1 Annex B. 
According to 1TR67 this option *is* in use in Germany. 

ETS 300 092-1 by default requires a strict checking of the calling number 
(paragraph 9.3). An alternate method available by special ararngement 
(paragraph 9.4) allows the sending of unscreened calling numbers. In this 
later case Annex B allows the network to add the network provided calling 
party number after the unscreen part. 

> > Some hacking of libpri is probably 
> > needed to handle this. To handle it cleanly a more complex interface 
> > between chan_zap and libpri may be needed.
> i think i will open a bug and dicuss how to implement this issue.
> i think both number are of interest, but the behaviour of the other 
> telco equipment should be retained... showing the unscreened number.

At least the standards are clear. There can be at most two calling party 
number IEs. One "User provided, unscreened" and one "Network provided". 
This is the only combination of two calling party numbers that are 
allowed. In all other cases there will only be one caller id in the setup 
message.

Peter