Missed call communication protocol

[Richard Bennett]

On Thursday 08 February 2007 09:01, Alexandre Ghisoli wrote:
> > Sorry to throw a spanner in the works but I'm not sure that this will
> > work here. It may work in other countries. I think I heard about it
> > working in the US.
>
> I'll second that for switzerland.
>
> When you subscribe for a E1 channel or direct VoIP trunk, you cannot
> send full e.164 number, but only the last digits that stick in the range
> of number the telco gave (rent ?) to you.
Now that you mention it I have noticed that sometimes to during testing, but 
not always.

> Now, for law enforcement, you are *NOT* allowed to change your clip on
> the network.
Ok, if that is the case then using the CLI won't fly beyond skunkworks anyway.

> 2/ For ISDN network (Q.931 signaling), use of the UserInfo field, on the
> signaling session (yes, you can send some byte when the phone is
> ringing, without charge)
Ok... Are you sure you don't mean the 'Display' field in the ISDN SETUP 
message? I can't find references to a UserInfo field in q931.
http://www.cotse.com/CIE/Topics/126.htm

Apparently the Q.931 protocol limits the maximum length of the Display Field 
information element to 44 octets, that should mean one can use 44 characters 
for a message without opening the line, which would be fine.

It seems that GSM should support the full range of ISDN messages,
http://kbs.cs.tu-berlin.de/~jutta/gsm/js-intro.html
so I'm wondering, why is no one using this for enhanced caller-ID, or similar 
applications. Where's the catch?

Richard.