Reference Guide for the Model XM128 ISDN Digital Modem
Advanced ISDN 7-13
User-To-User Information
The Model XM128 modem supports user-to-user information exchange via the D channel. To
transmit a message, use the ATT4<message.....> command. The angle brackets (< >) are part of
this command. The message is included in a user-to-user information element, which is sent with
the first valid message that follows.
If the ATT4<message.....> c ommand is issued before dialing, the user-to-user information element
is sent in the setup message. Whether the information element can be sent to the called party or not
is switch dependent. If the switch supports this information element, the called party can see the
message before the call is answered.
During a call connection session, the D channel is still used to exchange user-to-user information.
For the single stream configuration, both sides must b e in Escap ed state because only t hen can the y
send the AT commands and view the responses.
The user-to-user information element is a supplementary service that has to be invoked on a
per-call basis.