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FAX-L1000 Chapter 5: Appendix
3.6.6 ISDN Protocol Messages
Main messages which are used in the communication protocols of Layer 2 - Layer 3 of the
control channel’s D-channel and Layer 2 - Layer 6 of the information channel’s B-channel are
listed.
a) D-channel messages
Layer 2
Message Description Remark
SABME Set Asynchronous Balanced The first thing sent when layer 2 is set.
Mode Extended
UA Unnumbered Acknowledge A reply message for SABME, DISC.
DISC Disconnect Sent when layer 2 is released.
Layer 3 (Continue)
Message Description Remark
SETUP Request for call settings First sent by the calling party after setting
layer 2 when making call settings. For the
called party, it does not matter whether or
not layer 2 is connected, SETUP will be
done anyway. Then, if layer 2 has not been
connected on the called party, it will be
connected, and following that CONN, etc.
will be sent.
SETUP ACK SETUP Acknowledge SETUP confirmation (request for
additional information).
CALL PROC Call Proceeding This means that the calling party SETUP
has been received by ISDN. It is an option
message.
CONN Connect On the calling party, receives when the
other terminal has responded. On the called
party, sent for accepted SETUP when able
to respond.
CONN ACK Connect Acknowledge On the calling party, sent for received
CONN. On the called party, ISDN sent for
the transmitted CONN.
ALERT Alerting On the calling party, receives when the
other terminal is in a call. On the called
party, sent when the user is in a call. It is an
option message.
DISC Disconnect Sent when layer 3 is disconnected.
Receives when disconnected from ISDN.