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Page 20 NDA-30115 Revision 1.0
Message Descriptions Property Management System - Communication Interface
• Recovery Start Report -- After receiving the Nop Test Recover Answer
message, the PMS must download NEAX database information (see “Room
Recovery (Model 60)” on page 27 and “Room Recovery (Model 90)” on page
28). This message notifies the NEAX of the incoming download.
• Recovery End Report -- Reports to the NEAX that the PMS database download
is complete.
• Data Link Release Request -- Used by either system to request a temporary
release of the data link.
• Data Link Release Confirmation -- Reply to the above message to acknowledge
data link release request.
• Extension Number Request -- Used by the PMS to request the current status of
extension numbers.
• Nop Test -- Under the standard protocol the PMS must send this message at
least every 60 seconds, but not less than 500 milliseconds, to demonstrate that
communication has been maintained.
Data Link Failure
Either system may recognize a loss of communication by one or more of the
following events:
• Lack of system traffic for a 60 second interval: the Nop Test message from the
PMS and the Nop Test Answer message (either Normal or Recover) from the
NEAX insure that at least one message should be received less than every 60
seconds.
• Detection of hardware problems within the physical data. Note that the NEAX
will put EIA pin number 6 (Data Set Ready) into the off state, indicating data
set not ready, when the data link has been effectively turned off in the NEAX,
either for maintenance or because of repeated, excessive errors.
• Excessive protocol errors (NAK’ed transmission, ENQ’s with no ACK/NAK
response).
• Other conditions, such as unavailability of buffers or queuing capability, which
result in an implied status change message which cannot be communicated to
the other system.
• Release of the data link requested and confirmed.
A data link failure will necessitate a database room exchange recovery procedure
only if any implied status change cannot be communicated to the other system and
cannot be queued for later transmission. If no messages have been lost, and can
instead be retransmitted, no database recovery is necessary.