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DESCRIPTION AND OPERATION
INIPT02 INFI-NET TO PLANT LOOP TRANSFER MODULE
I-E96-613A
2 - 5
Status Reporting
The IPT module reports its own status. Exception reporting for
status occurs whenever there is a change in status or every 60
seconds if no change occurs.
Communication Protocol
The IPT communication protocol consists of two layers:
•
Link control layer.
•
Application layer.
The link control layer is a sequenced delivery system with posi-
tive acknowledgment and automatic repeat request for error
recovery. The application layer in both the central and remote
satellite loop IPT modules uses the link control layer to trans-
port control and configuration information and exception
reports.
FRAMING
The IPT module uses message framing to help it track data
bytes that pass through the asynchronous communication
link. The receiving IPT module looks for a one-byte character at
the start of every transmission. Once it recognizes the synchro-
nization character, it looks at a byte count field in each mes-
sage to determine the framing of successive messages.
SEQUENCE CONTROL
All messages have a sequence number. The transmitting and
receiving IPT modules use the sequence number to keep track
of outstanding, lost and bad messages.
LINE CONTROL
Line control limits the transmission time of each IPT module
when both IPT modules are in the half duplex mode. There are
two limits. They are the window of outstanding sequenced
messages and the maximum transmission time set by execu-
tive block (function code 203) specifications. When the trans-
mitting module reaches one of the limits (or has no more data
to send), it flags the last message in the transmission. When
the receiving module sees this flag it can then start a transmis-
sion sequence of its own. If the transfer modules are in the full
duplex mode they do not use line control. They can transmit
independently of each other.