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⟦73ce29bc5⟧ Wang Wps File
Length: 9298 (0x2452)
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Notes: Spelunked
Names: »~ORPHAN75.08«
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└─⟦17da89677⟧ Bits:30006229 8" Wang WCS floppy, CR 0126A
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WangText
T̲A̲B̲L̲E̲ ̲O̲F̲ ̲C̲O̲N̲T̲E̲N̲T̲S̲
4.4 MESSAGE COMPILATION UNIT (MCU) ............
4.4.1 General ...............................
4,4,2 Compilation algorithm .................
4.4.2.1 Character Status ..................
4.4.2.2 Channel Status ..................
4.4.3 MCU Design ............................
4.4.4 Functional Description ................
4.4.5 Interface Characteristics .............
4.4.5.1 Modem Interface ....................
44.5.2 Crypto Interface ..................
4.4.5.3 MPF Interface .....................
4.4.6 Comparison with requirements ..........
…86…1 …02… …02… …02… …02…
4.4 M̲E̲S̲S̲A̲G̲E̲ ̲C̲O̲M̲P̲I̲L̲A̲T̲I̲O̲N̲ ̲U̲N̲I̲T̲ ̲(̲M̲C̲U̲)̲
4.4.1 G̲e̲n̲e̲r̲a̲l̲
The MCU solution proposed by Christian Rovsing A/S
is based on a military qualified, off-the-shelf micro-
processor system
Fig. 4.4-1
The message compilation Unit receives four serial data
streams from four ship-to-shore access sites. The
four data streams are identical except for transmission
errors and delay.
From the four channels, a single channel is compiled
by a majority voting algorithm and delivered to the
KW 7 crypto.
The functional characteristics of the proposed MCU
are
1.Reception of four 75 Baud V.24 channels.
2. Compensation for relative transmission delay on
the four channels (20msec).
3. Calculation of statistics for the purpose of determining
the probability of a correctly received character
from a particuar channel (channel confidence).
4. Selection of most probably correct character among
the four; the selection is based on the current
channel confidence, combined with the character
status in term of framing status and correlation
with the otherthree channels.
5. Transmission of the character on a V24 line to
the Crypto.
6. Provision of a character on a separate line to
the MPF, indicating whether the confidence level
of the character passed a threshold or not.
7. Provision of a chanel confidence figure at regular
intervals.
4.4.2 C̲o̲m̲p̲i̲l̲a̲t̲i̲o̲n̲ ̲a̲l̲g̲o̲r̲i̲t̲h̲m̲
The IFB requires a message compilation by majority
voting on a character-by-character basis. Heavily
garbled channels shall be excluded from the voting
process. In addiion, a confidence level of the channels
shall be established in order to facilitate selection
of the most probably correct character in case the
majority voting is ambiguous.…86…1 …02… …02… …02… …02…
Since no a priori assumptions can be made about the
information in the message, the parameters left for
assigning a confidence level of a given character among
the four received ae:
Character status:
o Received/not received status
o Correct/incorrect framing (start/stop bit)
o Agreement/non agreement between channels
Channel Status:
o Channel confidence level based on the status of
the previously received characers.
4.4.2.1 C̲h̲a̲r̲a̲c̲t̲e̲r̲ ̲S̲t̲a̲t̲u̲s̲
The character status is easily achieved. It should,
however, be emphasized that the errors are strongly
interrelated so a thorough knowledge of the failure
mechanisms is necessary for the correct interpretation.
Framing error, as an example, could be caused by
a) bit error on start bit
b) bit error on stop bit
c) bit slippage
Case a) Causes in general a data bit to be mistaken
for a start bit and hence leads to a garbled character.
Bit error on stop bit gives the same error indication,
but the charactr will be correct. Bit slippage will,
in general, lead to a garbled character, but an error
indication will only be given in certain cases.
4.4.2.2 C̲h̲a̲n̲n̲e̲l̲ ̲S̲t̲a̲t̲u̲s̲ ̲
Determination of the method for achieving the channel
status is quite complex
The purpose of the channel status (channel confidence
level) is to provide a figure which reflects the relative
(priria facie) probability of receiving a correct character
from a given channel.
A means for determination of this probabiity is afiltered
version of the history of character status. The filter
function should, ideally, be based on a comprehensive
statistical modelling of the entire transmission channel.
However, a sufficiently good result can fortunately
be achieved with lss work because the model is dominated
by a few contributing mechanisms. Some of the more
important aspects of the filter function are:
o The hardware/software complexity required for the
realization
o The ability to react rapidly on burst errrs
o The ability to recover quickly from burst errors
o Smooth initialization.…86…1 …02… …02… …02… …02…
4.4.3 M̲C̲U̲ ̲D̲e̲s̲i̲g̲n̲
Fig. 4.4-2
The MCU functions are performed by two LTUX-M-CPU plug-in
modules, housed in a small crate with power supply.
The LTUX-MCPU is a module designed for intelligent
line termination of multiple (up to 4) V.24 type channels.
The on-board microprocessor is programmed for the
individual application and the program resides in a
PROM.…86…1 …02… …02… …02… …02…
The two modules communicate via the microbus.
Fig. 4.4-3
The input module performs the serial-to-parallel conversion,
collects the framing status and compares he characters
to achieve the correlation figure.
The output module receives the four characters and
the corresponding status and performs all message compilation,
data output and character quality assignment.
4.4.4 F̲u̲n̲c̲t̲i̲o̲n̲a̲l̲ ̲D̲e̲s̲c̲r̲i̲p̲t̲i̲o̲n̲
The four serial, asynchronous data streams are converted
to parallel data by a universal asynchronous receiver/transmitter
(UART).
This digital cicuit provides an indication of framing
error, i.e. incorrect frame format caused by , for
example, a falsely detected start bit or a corrupted
stop bit.
A "data available" status is indicated as a separate
signal when a character has been receive.
The received characters, together with the corresponding
status, are read from the UART'S after the expiry of
the max. delay period (20 msec) after the character
of the leading channel has been completed.
For each channel the following informtion is derived:
Data available yes/no
Framing error yes/no
Correction, Fc 0,1,2 or
3
Fc is the number of channels which show the same characte
as the one in question, i.e. FC = 3 means that all
four channels agree, FC = 0 that no other channel agrees
with the one in question.
Table look-up is a fast, very flexible and inexpensive
method of implementing algorithms, in particular if
the able size is small.
Data available, error and F…0f…c…0e…, together with channel
confidence are used for table-look-up of
a) Confidence level for present character
b) Updated channel confidence
The contents of the table are determined to fulfil
the specific requirements of the IFB on exclusion of
garbled channels. The remaining degrees offreedom
are used to provide the optimum choice based on the
statistical properties of the channel and taking into
account the behaviour during initialization, burst
error, etc.
Having achieved the character confidence level, it
takes only a simpl comparison to select the character
with the highest value for output.
Should more than one channel hold the same character
confidence level but claim different character values,
the one which was selected for the previous character
is chosen (prvided this channel is among the channels
which hold the high level) or the one with the lowest
channel number is chosen for output. In this case,
the character transmitted simultaneously on the status
line will indicate the ambiguity.
For each bock of TBD compiled characters or after TBD
seconds of silence, a status message is sent on the
status line in addition to the above character quality.
The status message contains four characters, reflecting
the current channel confidence level.
4.4.5 I̲n̲t̲e̲r̲f̲a̲c̲e̲ ̲C̲h̲a̲r̲a̲c̲t̲e̲r̲i̲s̲t̲i̲c̲s̲
From mains supply…86…1 …02… …02… …02… …02…
4.4.5.1 M̲o̲d̲e̲m̲ ̲I̲n̲t̲e̲r̲f̲a̲c̲e̲ ̲
The MCU inputs are V.24/V.28 asynchronous channels.
Data rate is 75 baud.
Connection is via standard 25 pole connectors.
4.4.5.2 C̲r̲y̲p̲t̲o̲ ̲i̲n̲t̲e̲r̲f̲a̲c̲e̲
The MCU interfaces to the crypto through a KW-7 adaptor.
The MCU output to the KW-7 adaptor is a V.24/V.28
compatible line. Connection is via standard 25 pole
connector.
4.4.5.3 M̲P̲F̲ ̲I̲n̲t̲e̲r̲f̲a̲c̲e̲
The status line to the MPF is an asynchronous V./V.28
line.
Data rate is 1200 Baud.
Connction is via standard 25 pole connectors.
4.4.6 C̲o̲m̲p̲a̲r̲i̲s̲o̲n̲ ̲w̲i̲t̲h̲ ̲r̲e̲q̲u̲i̲r̲e̲m̲e̲n̲t̲s̲
The MCU, extended with the KW-7 adaptor, complies with
the requirements of the IFB in all respects
