4-12 Message structure and function
297-2521-106 Standard 23.01 March 2001
Table 4-1
Q.931 message descriptions
(continued)
Message Event informationDirectionMeaning
PROG Progress The network or the originator
sends this message.
Indicates the progress of a call
during call establishment (for
example, when the call has left
the ISDN network or to indicate
the use of in-band tones. Sent
to the originator any time after
a CALL PROC message is sent
Examples:
• Call is not end-to-end
ISDN. The connection from
source to destination
includes a PTS trunk.
• In-band information is now
available. An event has
occurred that must be
retold to the originator of
the call. When this
information cannot be sent
out of band on the
D-channel, the information
is sent as a treatment on a
B-channel.
REL Release Sent from either the calling
party or the network to
indicate: the equipment
sending the message
disconnected the channel and
intends to release the call
reference; and the receiving
equipment should release the
channel and call reference
and abort any call with that
call reference in the process
of being set up.
Sent to the member that sent
the disconnect message. This
is the second step in the call
takedown message sequence.
A REL message is also sent for
abnormal call clearing.
—continued—
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