Nortel DMS-250 - Page 61

Message structure and function 4-13
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Table 4-1
Q.931 message descriptions
(continued)
Message Event informationDirectionMeaning
REL COM Release
complete
Sent from either the calling
party or the network.
Indicates the equipment
sending the message released
the channel and call reference;
the channel is available for
reuse; and the receiving
equipment will release the
channel and call reference.
This is the last message sent in
any disconnect sequence. Also
sent in response to a SETUP
message when the requested
B-channel cannot be allocated.
Generates after a member
receives a REL message. This
is the third and final step in the
call takedown message
sequence.
REST Restart Sent from one side of the
interface to the other to
request the recipient to restart
(return to an idle condition)
the indicated channel(s) or
interface.
This message is of local
significance. It uses the global
call reference. If no channel is
identified, the restart applies to
all B-channels controlled by the
D-channel on which the
message was sent.
REST ACK Restart
acknowledge
Sent to acknowledge receipt of
the REST message. Indicates
the requested restart is
complete. REST ACK is of
local significance. It uses the
global call reference.
SERV Service Bidirectional; can be sent by
either the calling party or the
network.
Conveys PRI B-channel
change of status to in-service,
maintenance, or out-of-service
state. Cannot be used for
changing the status of the
D-channel.
SERV ACK Service
acknowledge
Bidirectional; can be sent by
either the calling party or the
network.
Used to acknowledge changes
to the status of PRI
B-channels. Sent in response
to a SERV message received.
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