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DESCRIPTION AND OPERATION
OPERATION OF SERIAL DATA CHANNELS
2 - 6
I-E96-613A
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ERROR DETECTION AND RECOVERY
A 16-bit cyclic redundancy check (CRC) code assures the integ-
rity of each transmission. The transfer module uses an auto-
matic repeat request to recover from errors. The receiving IPT
module notifies the sending IPT module of the last sequence
number it receives. The sending module then knows which
message packet to send again.
START-UP CONTROL
If either IPT module is restarted, it sends a message to the
other IPT module so that it can take the steps needed to resyn-
chronize itself with the restarted transfer module.
Redundancy
Redundancy requires a full set of duplicate modules (four NIS,
IPT and MPI modules). The secondary transfer module contin-
uously monitors the primary (over the Controlway or module
bus). A failover occurs when the secondary IPT module detects
a primary module failure on the module bus or Controlway.
When this happens, the secondary assumes responsibility and
the primary is taken off-line. The new primary IPT module
brings its NIS module on-line.
OPERATION OF SERIAL DATA CHANNELS
Command and data transfer across the IPR interface is
through an asynchronous RS-232-C interface. This interface
operates in half or full duplex modes at 300 to 38,400 baud
using eight-bit characters and various combinations of parity
and stop bits.
Messages passed across the serial data channels are formatted
in propriety message formats optimized for transfer of
INFI-NET and Plant Loop data. A sliding window acknowledge
protocol is used where each end of the IPR interface can have
several messages outstanding which are acknowledged in
sequential order by the opposite side. Messages are automati-
cally retried until they are received correctly and acknowledged
by the opposite end.