PCM30U, PCM30U-OCH – User's, Operating and Maintenance Manual
E.1.5 Security (in general)
PBS transmits data in 64bit blocks called packets. Block contains state of commands (doubled for 1-6
command), CRC of 12
th
order, synchronization and management channel. Management channel and part of
synchronization are not covered by CRC. Synchronization is spread around whole packet I order to improve
resilience against false synchronization.
Additional security shall be obtained by “repeating” requesting 2 or 4 equal states of received commands to
act at outputs.
This result in following “probability of unwanted command” P
uc
.= 3.2 10
9
*p
13
, where p equals BERR.
Inputs are periodically (every 500μs @128 kbit/s) sampled and coded into this packet.
E.1.5.1 Continual test
Packets are transmitted and received continually (every 500μs @128 kbit/s), that means both local and
remote PBS are under full check as well as transmission path.
Next more this test uses back acknowledgment bits located in packet. Every received command is
transmitted back to source as an acknowledgment of transmission. This test is performed every 10 ms
E.1.5.2 Button Test
This test is intended to be used at commissioning time or at “troubleshooting procedure”. Purpose is to check
individual LEDs and routing when PBS with “two direction” feature is used.
Test can be initiated only by pressing Test button at unit for time longer then 500 ms. Test cannot be initiated
when command is active. Since it takes some time (approximately 500 ms) to stop the Test, it cannot be
used under full operational mode, because transmission time could not be granted.
E.1.5.3 Button test sequence
Test initiated by button at PBS1. “Start of Test” record is written to alarm log.
PBS1 disconnects inputs and outputs.
PBS1 transmits “Test state” to PBS2
PBS2 blocks outputs, creates “button test loop” and confirms test state
PBS1 simulates step-by-step individuals commands and check that they come back.
LED indicates command being tested, flashing green LED indicates failure at individual command.
“Test state” must be canceled at both PBS to return to operational state.
“End of Test” - “success” or “failure” record is written to alarm database
IN 1
IN 10
OUT 1
OUT 10
coding
security
command
back ack
command
PBS1 PBS2
2 packets/ms
(128 kbit/s)
button
test
loop
permanent
test loop
in / out
discon
nection
Power Channel Modules E-10 446S037.914.14N00
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