Missed call communication protocol

Alexandre Ghisoli alex at ghisoli.ch
Thu Feb 8 09:01:21 CET 2007

Le mercredi 07 février 2007 à 16:08 +0200, Rodney Arne Karlsen a écrit :
> Hi there
> While you can choose your callerID when using a sip server, it may not stay 
> the way you set it once it passes through the PSTN gateway. I tried playing 
> with CallerID stuff some time back here in South Africa and our PSTN provider 
> will only allow you to set your caller ID to a number that is assigned to the 
> line you are using. If you are lucky enough to have a PRI line then you start 
> with around 100 numbers. 
> 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.

There are some supplemental services, like Special Arrangement (SA),
that let you send full numbers, without controlling from the telco side
if you stay in your range (in fact, your real number still sent on the
network, but a supplemental field is added with the number you want to

Now, for law enforcement, you are *NOT* allowed to change your clip on
the network. 

To solve this issue, I see 2 directions : 

1/ Ask for a SS7 trunk, to get more powerfull abilities (cell
localisation, supplemental services, direct access to radio, ...)
but telco will charge you for that, and a big access fee :( Also you
need a SS7 endpoint.

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)

Probably for all European countries this will be the same.

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