Nortel DMS-250 Reference Manual page 61

Table 4-1
Q.931 message descriptions
Message Meaning
REL COM Release
complete
REST Restart
REST ACK Restart
acknowledge
SERV Service
SERV ACK Service
acknowledge
(continued)
Direction
Sent from either the calling
party or the network.
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.
Bidirectional; can be sent by
either the calling party or the
network.
Bidirectional; can be sent by
either the calling party or the
network.
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
Message structure and function 4-13
—continued—
Event information
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.
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.
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.
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.
Used to acknowledge changes
to the status of PRI
B-channels. Sent in response
to a SERV message received.