Message structure and function 4-9
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Table 4-1
Q.931 message descriptions
Message
Meaning Direction Event information
ALERT Alerting Sent by the called party to the
network and by the network to
the calling party to indicate
that called party alerting has
been initiated. Any additional
information in this message
(such as redirecting number
or redirection number) is not
sent to an originating ISDN
user. Instead, the network
ignores these information
elements upon receipt.
Sent to the originator to
indicate alerting of the called
party; sent to PRI originators
only when received from a
terminating PRI agent. The
terminating MSL-PBX
determines when the alerting
message is sent.
For PRI-to-trunk calls, the
B-channel cut-through occurs
between call proceeding and
connect.
CALL PROC Call
proceeding
The network sends this
message to the originating
PRI to indicate call
establishment has been
initiated and that it will accept
no more information. Also, the
terminating PRI may send this
message to the network.
When the network receives
this information, it does not
send it back to the originator.
This message does not have
end-to-end significance. Its
significance is local within a
single interface.
Sent to the originator of the call
after translation and routing
have been successful.
CONG CON Congestion
control
Sent by either the network or
the congested called user to
the sender of the USER INFO
message.
Indicates the called user or
network is congested and
unable to receive the USER
INFO message. All subsequent
USER INFO messages are
discarded. A STATUS message
is sent to the sender of the
USER INFO message with the
Cause, Coding Standard, and
Location.
—continued—
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