> When using QSIG the PABX sends a SETUP message when I try to call from
> a telephone connected to the PABX. Sometimes I get the following
> information element last in the SETUP message:
> 0x7E 0x01 0x04
> I have looked in ETS 300 172 but can't find what information element
> it can be. So my question is what is it, and where can I find
> information about it?
This should be a User-User-Info IE.
$01 length indicator
$04 protocol indicator: IA5 characters
This parameter can be used by some ISDN telephones to transmit one of
some predefined text strings (in your example it's just an empty
string), but for the transmission over public network your access
usually needs an extra authentication for UUI (remember, the
information is transmitted at call-setup time and if the called
subscriber doesn't answer the call you could send information free of
charge...). A private network may handle this in another way.
Take a look into ITU-Rec. Q931 if you want to know more.