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⟦0e25186d4⟧ Wang Wps File
Length: 38723 (0x9743)
Types: Wang Wps File
Notes: DATA TRANSMISSION PROTOCO
Names: »1914A «
Derivation
└─⟦780c36067⟧ Bits:30006094 8" Wang WCS floppy, CR 0146A
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WangText
…0a……00……00……00……00…$…0a……00……00…$…0b… …0a… …02……1f……09……1f……02……1e……09……1e……00……1e……86…1 …02… …02… …02… …02…
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1̲.̲ ̲D̲A̲T̲A̲ ̲T̲R̲A̲N̲S̲M̲I̲S̲S̲I̲O̲N̲ ̲P̲R̲O̲T̲O̲C̲O̲L̲S̲
1̲.̲1̲ ̲G̲e̲n̲e̲r̲a̲l̲
There are two kinds of teleprocessing: direct and indirect.
Indirect teleprocessing requires data stored locally at source,
data are transferred via datastations to their destination,
which is usually also the location of the host computer. Data
are stored on a storage medium, and are then processed in a
second step (off-line).
Using direct datatransmission, data are directly input into
the host computer, processed and then stored on a storage medium
(on-line).
Relative to a specific computer the following modules are required
at the host computer for direct data transmission:
a. Datatransmission Unit (DU)
consisting of line buffers (LB) and hardware
datatransmission controller (DC)
b. Operating System
(Disk Operating System = DOS) software
c. Datatransmission System (DS) with
communication programs
1̲.̲2̲.̲ ̲O̲v̲e̲r̲v̲i̲e̲w̲ ̲o̲n̲ ̲p̲r̲o̲c̲e̲d̲u̲r̲e̲s̲ ̲u̲s̲e̲d̲
1̲.̲2̲.̲1̲ ̲S̲e̲c̲u̲r̲e̲d̲ ̲b̲a̲t̲c̲h̲-̲ ̲a̲n̲d̲ ̲d̲i̲a̲l̲o̲g̲u̲e̲ ̲p̲r̲o̲c̲e̲d̲u̲r̲e̲s̲
The described procedures contain the Basic-Mode-Proposals, which
have been agreed by international working groups (ISO, ECMA,
etc.) in order to maintain compatibility of products from all
computer and terminal manufacturers. There are 5 phases of datatransmission:
1. Link establishment
2. Initiation of datatransmission
3. Transfer of text
4. Terminating transmission
5. Link close-down
The link establishment does not belong to the procedure, the
link close down can be initiated by the procedure.
The procedures can take account of the following measures:
a. In case of distorted control characters, transfer of
text will automatically be maintained.
b. Error detection and error recovery in case of corrupted
text
c. The datatransmission control characters are recognized
(TC-Transmission-Control-Character) and processed.
d. Normally the ISO-7Bit Code and CCITT No. 5 are used.
e. The Datatransmission Unit is alternating (mutual information
flow)
f. Synchronous and asynchronous modes (in synchronous
mode also transparent mode for transmitting packed
decimals and computer programs in machine language).
1̲.̲2̲.̲2̲ ̲D̲i̲a̲l̲o̲g̲u̲e̲ ̲p̲r̲o̲c̲e̲d̲u̲r̲e̲s̲ ̲w̲i̲t̲h̲ ̲o̲u̲t̲p̲u̲t̲ ̲o̲f̲ ̲u̲n̲s̲o̲l̲i̲c̲i̲t̲e̲d̲ ̲m̲e̲s̲s̲a̲g̲e̲s̲
These procedures permit pure dialogue traffic and dialogue
traffic with unsolicited messages. Unsolicited messages
are originated at any time by the host computer without
prior request by the datastation (DSt). In addition pure
input is possible.
There is only the Transfer of Text phase in this procedure.
The initialization of the dialigue (request from the DSt,
response from the host computer) always takes place at
the data station. In case of no response from the host,
respectively if no response is provided for, repeated
input to the host computer is possible (pure input). The
procedure can be applied synchronously or asynchronously
using different codes. Erroneous data are marked as such.
Error recovery is left to the user.
1̲.̲2̲.̲3̲ ̲D̲i̲a̲l̲o̲g̲u̲e̲ ̲p̲r̲o̲c̲e̲d̲u̲r̲e̲ ̲r̲e̲q̲u̲e̲s̲t̲/̲r̲e̲s̲p̲o̲n̲s̲e̲
In this procedure there is only the Transfer of Text phase.
Only asynchronous mode using a variety of codes is possible.
The DSt initializes, i.e. issues a request and the host
computer issues a response or an acknowledgement. Pure
input is also possible.
1̲.̲2̲.̲4̲ ̲I̲n̲p̲u̲t̲ ̲o̲r̲ ̲o̲u̲t̲p̲u̲t̲ ̲p̲r̲o̲c̲e̲d̲u̲r̲e̲
Only pure input or pure output is possible.
1̲.̲3̲ ̲E̲l̲e̲m̲e̲n̲t̲s̲ ̲o̲f̲ ̲a̲ ̲P̲r̲o̲c̲e̲d̲u̲r̲e̲
The sequence of a procedure can be determined from the
flow diagrams, which are associated to each procedure
descriptions. A procedure can only be executed after determination
of the operating method (direction of transmission, control
method, transmission codes, structure of character sequence,
error recovery, etc.). The parameters below define the
operating method:
1. Direction of Transmission
2. Permission to start Data Transmission (Initialization)
3. Structure of character sequence
4. Transmission code
5. Error recovery
6. Transmission modes (synchronization method)
7. Time-outs
In addition, agreements about operations within the datanetwork
are important. The procedures do not provide for measures
to recognize errors, which have not been caused by data
transmission. Those errors must be treated by the data
terminal, the system software and the application software.
1̲.̲4̲ ̲P̲a̲r̲a̲m̲e̲t̲e̲r̲s̲ ̲o̲f̲ ̲a̲n̲ ̲o̲p̲e̲r̲a̲t̲i̲n̲g̲ ̲m̲e̲t̲h̲o̲d̲
1̲.̲4̲.̲1̲ ̲D̲i̲r̲e̲c̲t̲i̲o̲n̲ ̲o̲f̲ ̲t̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲
The following transmission directions are possible:
a̲.̲ ̲U̲n̲i̲d̲i̲r̲e̲c̲t̲i̲o̲n̲a̲l̲ ̲i̲n̲f̲o̲r̲m̲a̲t̲i̲o̲n̲ ̲f̲l̲o̲w̲ (simplex mode)
Operation is only possible in one direction.
Error correction by inquiry is not possible.
b̲.̲ ̲A̲l̲t̲e̲r̲n̲a̲t̲i̲n̲g̲ ̲i̲n̲f̲o̲r̲m̲a̲t̲i̲o̲n̲ ̲f̲l̲o̲w̲ (half duplex mode)
U̲si̲ng̲ t̲wo̲ w̲ir̲es̲: Transmission possible in either
direction but not both directions simultaneously.
Modems are switched via the interface link 105/2
from send mode to receive mode or vice versa;
switching requires a delay time. This delay time
is not necessary if GND-Units and teleswitchunits
are used.
u̲si̲ng̲ f̲ou̲r ̲wi̲re̲s: (fast turnaround): Same as
with two wires, except for the absence of switching
delays. The interface links 108/1 and 105/2 are
permanently in state "ON", the link 103/1 is
kept on "1" as long as the station does not send
data. The transmission path is capable for full
duplex usage.
m̲ul̲ti̲-p̲oi̲nt̲ c̲on̲ne̲ct̲io̲n (four wires) (party line):
In multi point connections the link 105/2 of
the called station must be switched.
c̲.̲ ̲T̲w̲o̲-̲w̲a̲y̲ ̲i̲n̲f̲o̲r̲m̲a̲t̲i̲o̲n̲ ̲f̲l̲o̲w̲ (duplex operations): Simultaneous
operation in both directions is possible. The
trans- mission speed is not relevant, i.e. the
auxilary channel can operate simultaneously with
the datachannel.
1̲.̲4̲.̲2̲ ̲S̲t̲a̲r̲t̲ ̲o̲f̲ ̲D̲a̲t̲a̲ ̲T̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲ (Initiative)
In teleprocessing systems, the station, which has permission
for initialization, carries the initative. One or more
stations can carry the initiative.
a̲.̲ ̲C̲o̲n̲t̲r̲o̲l̲ ̲s̲t̲a̲t̲i̲o̲n̲. In most cases the host computer
represents the control station. The host decides on
the sequence of data transmission in a datanetwork
by means of control methods (polling, selecting). The
host sends "requests to send" (polling) respectively
"requests to receive" (selecting) to the tributary
stations. There is always only one control station.
b̲.̲ ̲M̲a̲s̲t̲e̲r̲ ̲S̲t̲a̲t̲i̲o̲n̲.̲ ̲The station to send text, always
carries the initiative for datatransmission. The master
station initiates the request and termination phase
and monitors the text phase.
c̲.̲ ̲D̲a̲t̲a̲ ̲S̲t̲a̲t̲i̲o̲n̲ (DSt). In case of simple procedures
the DSt has the initiative. The DSt can issue requests
and the remote-station (e.g. the host computer) responds
to this input with an output. Only in case of unsolicited
messages the host computer carries the initiative.
1̲.̲4̲.̲3̲ ̲S̲t̲r̲u̲c̲t̲u̲r̲e̲ ̲o̲f̲ ̲C̲h̲a̲r̲a̲c̲t̲e̲r̲ ̲s̲e̲q̲u̲e̲n̲c̲e̲
The sequence of the data transmission control character
determines the flow of data transmission. Start and end
of text must be marked with control characters, as well
as error checks at the end of block or within the text.
The messages for data transmission are formatted in accordance
with the following charactersequence:
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲SOM TEXT EOM BCC ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲
SOM: Start of Message
EOM: End of Message
BCC: Block Character Check
Text can be transmitted in standard or transparent mode.
1̲.̲4̲.̲4̲ ̲T̲h̲e̲ ̲c̲o̲n̲t̲r̲o̲l̲ ̲c̲h̲a̲r̲a̲c̲t̲e̲r̲s̲ ̲f̲o̲r̲ ̲d̲a̲t̲a̲ ̲t̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲
The data transmission procedure requires a number of standardized
transmission control characters (= TC). They have a unique
meaning and cause certain reactions of the data transmission
controller. These characters may not be used within the
text, if transmission uses standard mode. Using transparent
mode, control characters are recognized by a preceding
DLE.
STX (TC2) Start of Text The control character STX
directly precedes each text
block. The 1st STX of each
text block causes reset
of the block check mechanism
to zero. Each further STX
contained in the block is
included in the block checking.
ETX (TC3) End of Text This transmission control
character terminates the
text. ETX is appended to
the last text block and
requests the receiveing
station to acknowledge immediately.
ETX is followed by a BCC
or BCS character. ETX is
included in the block checking.
EOT (TC4) End of Trans-
mission EOT signifies the end of
one or more text blocks.
The control station sends
EOT in order to prepare
a tributary station to receive
a request to send or a request
to receive.
Using party lines the master
station sends EOT in order
to return the permission
to send to the control station.
Using point-to-point connections
with equally privileged
stations, the master station
sends EOT in order to signify
end of transmission and
its return to idle state.
ENQ (TC5) Enquiry Request to a station to
respond. ENQ could include
the function "who are you",
which is required in case
of public dial-up networks.
If the host computer issues
a request to send (polling),
the control station sends
ENQ. If the DSt or the host
computer issues a request
to receive (selecting),
the master station sends
ENQ. ENQ signifies End of
Address if the host computer
issues request to send.
The same is true for selecting
if a response from the slave
station is expected.
Summary:
1. ENQ can terminate a request
to receive
2. ENQ can request identification
and/or station status information.
3. ENQ can terminate the
idle status of a transmission
line.
4. ENQ can request repeat
of acknowledgement in case
of error.
ACK (TC6) Acknowledgement ACK represents a positive
response from the text receiving
station to the master station.
During the initialization
phase ACK is sent as response
to ENQ from the control
station (e.g. host computer)
to the DSt, respectively
as response to ENQ from
the DSt to the host computer
in order to indicate ready
to receive. Additional station
identifiers must precede
the ACK. During the text
phase ACK is used to indicate
error free receipt of a
block.
DLE (TC7) Data Link Escape DLE changes the meaning
of succeeding characters,
i.e. it is possible to provide
supplementary control characters.
Only those characters which
are defined in the code
table may be used.
Conventions: If data transmission
control characters are used
as text characters, the
control functions for data
transmission are realized
by character sequences starting
with DLE and followed by
the respective transmission
control character.
DLE, EOT causes close down
of a dial-up line.
DLE is not included for
block checking if followed
by a control character.
If DLE is followed by DLE
only the 2nd DLE is included
for block checking. DLE,
SYN are not included for
block checking.
NAK (TC8) Negative
Acknowledgement Negative response to the
master station.
Conventions:
NAK is a "not ready to receive"
reply to a request to receive.
NAK is sent from the receiveing
station to indicate that
the previous transmission
block was in error and the
receiver is ready to accept
a retransmission of the
erroneous block. NAK precedes
supplementary information
in the response.
SYN (TC9) Synchronous Idle In synchronous mode SYN
is used to establish and
maintain synchronization.
SYN is used as a fill character.
Before transmission of a
textblock the receiver must
recognize at least 2 of
the SYN characters (3 resp.
7).
It may not be used as a
fill character between:
ITB BCC
ETB BCC
ETX BCC and within DLE
sequences. After each 1
s of text the sender inserts
SYN, SYN resp. DLE, SYN.
SYN is normally removed
by the receiver.
ETB (TC10) End of Trans-
mission Block In block mode ETB is at
the end of a text block.
If text is broken up into
blocks, each block is terminated
with an ETB except for last
block.
ETB is used to request immediate
acknowledgement from the
receiver. If block checking
is used, ETB is followed
by BCC resp. BCS.
ETB is included in the block
check.
ACK[/ACK1 Acknowledgement ACK[ resp. ACK1 are control
character sequences and
are directed as positive
acknowledgements from the
text receiver to the master
station (text sender). Response
to a request to receive;
station identities must
precede the ACK. Error free
text is acknowledged alternately
by ACK[ and ACK1. This permits
the sender to recognize
wheter all text blocks were
received.
ITB End of Intermediate
Transmission Block - ITB separates a text block
into text sections. It does
not cause acknowledgement
by the receiver (no change
in direction of transmission).
However block checking provides
a BCC (BCS) after each ITB
and the block check sum
is reset. Hence error recognition
is accomplished by section,
whereas acknowledgement
and error correction is
only applied for the whole
block.
ESC Escape ESC (switching) changes
the meaning of the succeeding
character. This character
can assume any value within
the code set, exclusive
control characters.
ESC is used to select the
correct I/O-device from
a number of devices connected
to a text receive station.
This is achieved by means
of an address byte which
follows STX ESC.
BEL Bell The BEL character is used
to communicate a signal
to the remote station before
or during data transmission.
It can e.g. be used to switch
to voice in case of malfunction.
After receipt of BEL the
station turns into the status
in which it were before
data transmission.
The following characters can be provided as optional supplements:
WABT Wait Before Transmit WABT is sent by the receiving
station, if temporary not
ready to receive.
During transmission of text,
WABT is sent instead of
a positive acknowledgement,
if the station is temporarily
(e.g. within 2 sec's) not
able to receive a new text-
block. The sending station
would normally react by
EOT or ENQ. …86…1 …02… …02…
…02… …02… …02… …02…
After receipt of ENQ the
receiving station keeps
sending WABT until it sends
ACK[ or ACK1 to show that
it is ready to receive text
again.
RVI Reserve Interrupt RVI represents a positive
acknowledgement and can
be used instead of ACK1
or ACK[. The acknowledgement
counter will be incremented
the same way as after ACK1/ACK[.
After RVI and if output
buffer empty the master
station finishes with EOT
and the receiving station
can now send.
TTD Temporary Text Delay TTD is sent by the sending
station, if the station
is not able to send a new
text block within 2 sec's.
This causes the receiving
station to send NAK: The
sending station can now
send:
1. another TTD
2. a new text block
3. an EOT
The control character sequences are described in the table
below:
6-Bit ISO 7-Bit-
Transcode Code USASC II EBCDIC
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲ ̲
ACK[ DLE - DLE [ DLE [ DLE (7[)…0f…16…0e…
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲
ACK1 DLE T DLE 1 DLE 1 DLE
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲ ̲
ITB US US US IUS
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲ ̲
WABT DLE W DLE ? DLE ? DLE"
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲ ̲
RVI DEL 2 DEL DEL DEL
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲ ̲
TTD STX ENQ STX ENQ STX ENQ STX ENQ
̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲
̲ ̲ ̲ ̲ ̲
1̲.̲5̲ ̲T̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲ ̲C̲o̲d̲e̲
1̲.̲5̲.̲1̲ ̲C̲h̲a̲r̲a̲c̲t̲e̲r̲-̲ ̲a̲n̲d̲ ̲C̲o̲d̲e̲ ̲F̲r̲a̲m̲e̲
The characters to be transmitted are binary coded with or without
parity bit. In start-stop mode (asynchronous), start and stop
pulses are added:
Stop parity Bit Bit Bit Bit Start
pulses bit 4 3 2 1 puls
code frame 1. information
bit on link
character frame
1̲.̲5̲.̲2̲ ̲D̲a̲t̲a̲ ̲P̲r̲o̲t̲e̲c̲t̲i̲o̲n̲
The following checking methods are used:
a. checking of data by character
- character parity check
b. checking by data block
- block parity check
- character and block parity check
- cyclic block checking
ad a): Each character is protected by creation of an additional
bit (parity bit).
Codes which contain an odd number of bits are complemented to
even. Codes which contain an even number of bits are left unchanged.
In this way it is possible to generate DEL or Bu by overpunching,
if e.g. a character has been punched incorrectly on a paper tape.
ad b): STX causes reset of the block check counter and is therefore
not included in the block check.
STX....Text....ITB
ETB BCC
ETX BCS
characters in-
cluded in the
block checking
The first DLE of a control character sequence (DLE DLE, DLE ETB,
...) is not included in the block checking.
B̲l̲o̲c̲k̲ ̲C̲h̲a̲r̲a̲c̲t̲e̲r̲ ̲C̲h̲e̲c̲k̲ ̲(̲B̲C̲C̲)̲
The sum (modulo 2) of the equally significant bits of all characters
of a block is complemented by means of an additional bit to even
parity. The sum of bits generated in this way from a text block
is the BCC character.
Example: S E B
T T C
X ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ X C
Bit-positions
b…0f…1…0e… 0 1111101 1 1
b…0f…2…0e… 1 1000011 1 0 representation i the
b…0f…3…0e… 0 0011110 0 0 ISO 7-bit code
b…0f…4…0e… 0 0101010 0 1
b…0f…5…0e… 0 1000001 0 0
b…0f…6…0e… 0 0000000 0 0
b…0f…7…0e… 0 1111111 0 1 Block Parity
0 1001011 1 0 Character Parity
B̲l̲o̲c̲k̲ ̲P̲a̲r̲i̲t̲y̲ ̲C̲h̲e̲c̲k̲ ̲i̲n̲c̲l̲u̲d̲i̲n̲g̲ ̲C̲h̲a̲r̲a̲c̲t̲e̲r̲ ̲P̲a̲r̲i̲t̲y̲ ̲C̲h̲e̲c̲k̲
In addition to generating a BCC character each character also
generates a parity bit.
C̲y̲c̲l̲i̲c̲ ̲B̲l̲o̲c̲k̲ ̲C̲h̲e̲c̲k̲i̲n̲g̲
In case of Cyclic Block Checking the check information consists
of two or more characters (BCS = Block Check Sequence).
The BCS is generated by an algorithm using the bits of the transmitted
information.
The polynomial below represents the algorithm for the 6-bit-code:
X…0e…12…0f… + X…0e…11…0f… + X…0e…3…0f… + X…0e…2…0f… + X + 1
1̲.̲6̲ ̲T̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲ ̲m̲o̲d̲e̲s̲
In order to be able to transmit data, sender and receiver must
be:
bit- and character synchronous.
1̲.̲6̲.̲1̲ ̲S̲t̲a̲r̲t̲ ̲-̲ ̲S̲t̲o̲p̲ ̲T̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲ ̲(asynchronous)
In this mode each character is preceded by a start pulse and
terminated by a stop pulse. The stop pulse can be of a length
of 1-; 1.5- and 2 times the bit length. The synchronism is achieved
by the leading edge of the start pulse and is maintained for
the duration of 1 character.
1̲.̲6̲.̲2̲ ̲S̲y̲n̲c̲h̲r̲o̲n̲o̲u̲s̲ ̲M̲o̲d̲e̲
Synchronism is achieved at the beginning of a character sequence
by a sequence of equal synchronization characters (SYN) and
is maintained for the duration of one data transmission block.
1̲.̲6̲.̲3̲ ̲T̲i̲m̲e̲ ̲O̲u̲t̲s̲
Time outs are used to prevent undefined states, which could
occur because of errors.
1̲.̲7̲ ̲N̲e̲t̲w̲o̲r̲k̲ ̲C̲o̲n̲f̲i̲g̲u̲r̲a̲t̲i̲o̲n̲s̲
Three different types of connections are possible in a data
network:
1. Point-to-point connection
2. Multi-point connection
3. Concentrator connection
1̲.̲7̲.̲1̲ ̲P̲o̲i̲n̲t̲-̲t̲o̲-̲P̲o̲i̲n̲t̲ ̲C̲o̲n̲n̲e̲c̲t̲i̲o̲n̲
Two datastations are connected to a line through which they
communicate. Normally one of the stations is the host computer,
whereas the other one is a DSt with one or more I/O devices.
1̲.̲7̲.̲2̲ ̲M̲u̲l̲t̲i̲-̲P̲o̲i̲n̲t̲ ̲C̲o̲n̲n̲e̲c̲t̲i̲o̲n̲
More than two subscribers are connected to one line. Only dedicated
links can be used as transmission lines. One station must represent
the control station (in most cases the host computer). Only
this control station can initiate data transmission by sending
time sequenced requests (polling and selecting) to the tributary
stations.
1̲.̲7̲.̲3̲ ̲C̲o̲n̲c̲e̲n̲t̲r̲a̲t̲o̲r̲ ̲C̲o̲n̲n̲e̲c̲t̲i̲o̲n̲
Two or more DSt are connected to the control station (in most
cases the host computer) via a concentrator. The control station
can initiate date transmission from/to one of the conneted DSts
by sending time sequenced requests (polling, selecting).
The DSts can also by polarity reversal of the send wire issue
a request to connect to the concentrator if they have text to
send.
1̲.̲8̲ ̲C̲o̲n̲v̲e̲r̲s̲a̲t̲i̲o̲n̲a̲l̲ ̲P̲r̲o̲t̲o̲c̲o̲l̲ ̲(̲R̲e̲q̲u̲e̲s̲t̲/̲R̲e̲s̲p̲o̲n̲s̲e̲)̲
P̲a̲r̲a̲m̲e̲t̲e̲r̲s̲
Information flow: Alternating
in
both
directions
(half
duplex)
Permission to begin
data transmission: Only
data
station
Protocol variation:
Message format: Transmission of text in block format, standard
mode:
SOM/ID*/...text.../EOM/BCC**/TRLR***
SOM (Start of Message) and EOM (End of
Message) can be represented by arbitrary
characters if CCITT-Code Nr. 2 is used.
The characters STX resp. ETX are used in
the widely applied 6,7 and 8 bit codes.
They may not appear within the text.
Synchronization
method: asynchronous
Data protection: character parity, block parity, character
and block parity (without cyclic checking)
Connection: point-to-point
Data stations: T̲e̲l̲e̲t̲y̲p̲e̲,
D̲a̲t̲a̲
̲d̲i̲s̲p̲l̲a̲y̲
̲u̲n̲i̲t̲,
P̲a̲p̲e̲r̲
̲t̲a̲p̲e̲
i̲n̲p̲u̲t̲
̲s̲t̲a̲t̲i̲o̲n̲
etc.
* Identity of DSt, only applicable to concentrator connections
** Block Check Charactor, only applicable to block parity
checking
*** TRLR = Tape trailer, only applicable to DSt with punch
tape input for request/response. The paper tape must
be punched with this arbitrary character till the
end.
F̲l̲o̲w̲c̲h̲a̲r̲t̲:̲
DSt sends Host computer DSt sends Host
computer
sends sends
Request Response Request Response
(Input) (Output) (Input) (Output)
Pause…0e…1…0f… Pause
SOM/Text/EOM SOM/Text/EOM SOM/Text/EOM SOM/Text/EOM
SOM/
Host computer Host
computer
has no response has
no
response
Error cases:
SOM/Text/EOM SOM/Text/EOM
SOM/Text/EOM
SOM/Text/EOM
T…0e…2)
SOM/Text/EOM Host computer DSt issues new
responds request or
SOM/Text/EOM/ with error repeats request
message
SOM/Text/EOM/ Host computer
does not respond
1) Required for pure input, at least = 100 ms (because
of data transmission program)
2) Time-out T = 25...50s is started at each received character
and is reset after EOM (Time-out of writing pauses).
The conversational protocol requires the DSt to issue
a request to the host computer which in turn produces
a response to the DSt. In case no response is provided
for upon an input, continued input of messages is possible.
Prior to begin of input, the connection between host computer
and DSt must be established as required.
Upon error recognition the link program transfers an error
message to the data transmission-application program.
In the flowchart above corrupted characters or character
sequences have been cancelled.
1̲.̲9̲ ̲C̲o̲n̲v̲e̲r̲s̲a̲t̲i̲o̲n̲a̲l̲ ̲p̲r̲o̲t̲o̲c̲o̲l̲ ̲(̲R̲e̲q̲u̲e̲s̲t̲/̲R̲e̲s̲p̲o̲n̲s̲e̲)̲ ̲m̲i̲x̲e̲d̲ ̲w̲i̲t̲h̲ ̲u̲n̲s̲o̲l̲i̲- c̲i̲t̲e̲d̲
̲o̲u̲t̲p̲u̲t̲
P̲a̲r̲a̲m̲e̲t̲e̲r̲s̲
Information flow: - Dialogue traffic mixed
with unsolicited
output
(half
duplex)
- Only unsolicited output
(simplex)
- Pure conversational traffic
(half
duplex)
Permission to begin data
transmission: Data station or host computer
Message format: Text transmission in one
block
SOM/...text.../EOM/BCC*/TRLR**
Synchronization method: asynchronous
Data protection: character parity, block
parity, character and block
parity (with cyclic checking)
Connection: Point-to-point connection
Data stations: Teletype, Data Visual
Display Unit, Paper Tape
Reader station.
Paper Tape Punch station.
* Block Check Character, only applicable to block parity
checking
**TRLR = Tape trailer, only applicable to DSt with paper
tape input in conversational mode. The paper tape must
be punched with this arbitrary character till the end.
F̲l̲o̲w̲c̲h̲a̲r̲t̲:̲
DSt sends Host computer DSt sends Host
computer
sends sends
request (input) response request (input) request
(output) (output)
D̲i̲a̲l̲o̲g̲u̲e̲:̲ Pause = 100 ms Pause
= 100
ms
SOM/Text/EOM 25s SOM/Text/EOM SOM/Text/EOM SOM/Text/EOM
SOM/... Host
computer
does not re-
spond
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲s̲:̲
SOM/Text/EOM SOM/Text/EOM
SOM/Text/EOM
SOM/Text/EOM
DSt issues new
request or re-
peats request
SOM/Text/EOM T…0e…+…0f… Host computer
issues error
message
SOM/Text/EOM -
SOM/Text/EOM Host computer
does not re-
spond Break in …0e…++…0f…
Unsolicited
Outputs SOM/Text/EOM SOM SOM/Text/EOM
10s
Character sequences corrupted during transmission have
been cancelled above.
* Required for continued inputs (caused by data transmission
program).
+ The time-out T = 25...50 sec is started in the host
computer at each received character and is reset after
EOM (Time-out of writing pauses).
++ A request from the DSt (SOM) coincides with an unsolicited
output (SOM) from the host computer: the host computer
waits for 10 s for a request. In case of no request
the host computer can start with unsolicited output
resp. continue with it.
The transmission protocol depicted above permits:
- conversational traffic mixed with unsolicited
output
- exclusively unsolicited output
- exclusively conversational traffic (including
pure input as a subset) optional with identity
exchange in accordance with the telex network.
The permitted type of traffic is dependent on the link
employed and is identified in the link program.
Messages have to be in the format:
SOM/...text.../EOM/TRLR
SOM (Start of Message) and EOM (End of Message) can be
represented by one or more arbitrary characters if CCITT
Code No. 2 is used for transmission. Using the widely
applied 6, 7 and 8 bit codes the characters STX resp.
ETX have been agreed. They may not appear in the text.
If the data modifier is used, the SOM has to be used for
input. In all other cases SOM is not absolutely necessary,
but recommended to be used.
A conversation (dialogue) consists of an input (request
by DSt) and a corresponding output (response to the DSt).
The initiative to start a conversation is always with
the DSt. If there is no provision for a response by the
host computer, another input can be made to the host computer
immediately. However because of the reactiontime of the
program of approximately 100 ms a delay is required between
two successive inputs.
Unsolicited outputs are initiated by the host computer.
An ongoing conversation must be finalized prior to output.
Depending on the type of line it might be necessary for
the host computer or the DSt to establish a link prior
to transmission. The host computer closes the link down
25 s after link establishment if there is no traffic resp.
after the last data transfer.
Erroneous messages which have been received by the host
computer are handed over to the data transmission application
program marked accordingly.
The protocol does not contain any provisions for repeating
erroneous blocks.
Usage of the telex network required exchange of identities
prior to message transmission.
The format of the identification is given below:
BU/WR/ZL/Z1/Subscriber no./ZWR/BU/DSt identification code/BU.
Subscriber no. = 6 characters
Identification code = 7 characters
1̲.̲1̲0̲ ̲P̲r̲o̲t̲e̲c̲t̲e̲d̲ ̲B̲a̲t̲c̲h̲-̲ ̲a̲n̲d̲ ̲C̲o̲n̲v̲e̲r̲s̲a̲t̲i̲o̲n̲a̲l̲ ̲P̲r̲o̲t̲o̲c̲o̲l̲
Protocol MSV1 MSV2
LSV1
LSV2
Information
Flow half duplex
link program AMS1 BMS2
AMS1 not
yet
available
control sta- text sending control
sta- text
sending
Initiative tion (always station tion
(always station
host c.) (master sta- host
c.) (master
sta-
tion) tion)
message standard mode standard
mode
format transparent mode
block separation with ITB
transmission
code USASCII, ISO-7-bit 6-bit-transcode,
EBCDIC
synchroniza-
tion method synchronous asynchronous
data character parity, block
character
parity, block
protection parity, character and parity,
character
and
block
block parity cyclic block parity
checking
network multi-point, multi-point,
configu- concentrators concentrators
ration
point-to-point
Parameters of the various protocols:
In principle each data transmission block is structured
as follows:
SOM/...text.../EOM
In basic mode SOM = STX and
EOM = ETX
or ETB
If block checking is used, the remote station responds
with
ACK or NACK
In transparent mode only character sequences are recognized
as data transmission control characters:
e.g. DLE STX is
interpreted
as STX
DLE ETX is
interpreted
as ETX
In standard mode DLE ETX, DLE ITB and DLE ETB are used
for reset.
1̲.̲1̲0̲.̲1̲ ̲P̲r̲o̲t̲e̲c̲t̲e̲d̲ ̲B̲a̲t̲c̲h̲-̲ ̲a̲n̲d̲ ̲C̲o̲n̲v̲e̲r̲s̲a̲t̲i̲o̲n̲a̲l̲ ̲P̲r̲o̲t̲o̲c̲o̲l̲ ̲M̲S̲V̲
̲1̲
with automatic error correction by retransmission of blocks
P̲a̲r̲a̲m̲e̲t̲e̲r̲s̲
Information flow:
half
duplex
Permission to begin
data transmission:
control
station
(mostly
host
computer)
Text mode:
standard
or
transparent
mode,
block
separation
by
ITB
Transmission code:
EBCDIC,
USASCII,
ISO-7-bit-code,
CCITT-Code
No.
5,
6-bit-transcode
Synchronization method: synchronous
Data protection: character parity, block parity,
character
and
block
parity,
cyclic
block
checking
Network configuration:
multi-point
(not
for
dial-up
lines)
point-to-point
Link program
AMS1 (in disk operating system (DOS))
Data stations:
Data
Visual
Display
Unit
M̲e̲s̲s̲a̲g̲e̲ ̲f̲o̲r̲m̲a̲t̲:̲ n * SYN/SOM/...text.../EOM
The codes used (see above) apply the data transmission
control character STX to represent the start character
SOM, and the characters ETB or ETX to represent the end
character EOM. If only one block is required to transmit
all text, the block ends with ETX; if more blocks are
required, all but the last block, which is terminated
with ETX, are terminated with ETB. Block Parity checking
requires the Block Character Check BCC and the Block Check
Sequence BCS (consisting of 2 characters) to follow ETB
resp. ETX. The remote station responds with an acknowledgement
(ACK, NAK). Text blocks can also be subdivided into text
sections by means of ITB:
STX/...text section.../ITB/BCC/...text section.../ITB/BCC....
No acknowledgement follows ITB; Acknowledgement is not
sent before the last text section of a block has been
terminated with ETB or ETX.
T̲r̲a̲n̲s̲p̲a̲r̲e̲n̲t̲ ̲m̲o̲d̲e̲ allows transmission of text in any arbitrary
code within an agreed character frame of 8 bit. The data
transmission control characters of the standard mode (ISO/CCITT-code
No. 5) are used. Transparent mode is switched on by DLE/STX
at the beginning of each text block and switched back
to standard mode by DLE/ITB, DLE/ETB or DLE/ETX. The preceding
DLE is needed to differentiate between control characters
and equal bit patterns within the text. If a bit pattern
which is equivalent to DLE, is part of the text, then
this DLE is duplicated to DLE/DLE. This duplicated DLE/DLE
is interpreted by the receiver as one text character.
Monitoring sequences (ACK, NAK, ENQ, EOT) are transmitted
in accordance with the codes of the standard mode. Each
text block and each monitoring sequence is preceded by
n SYN characters in order to achieve character synchronization.
In addition during the text phase two SYN (in transparent
mode DLE SYN) characters are inserted every 1 s. SYN characters
are n̲o̲t̲ depicted in the flowcharts below.
D̲e̲s̲c̲r̲i̲p̲t̲i̲o̲n̲ ̲o̲f̲ ̲t̲h̲e̲ ̲P̲r̲o̲t̲o̲c̲o̲l̲ ̲F̲l̲o̲w̲
There are 3 protocol phases: request, text transmission
and termination.
R̲e̲q̲u̲e̲s̲t̲ ̲t̲o̲ ̲s̲e̲n̲d̲ ̲r̲e̲s̲p̲.̲ ̲r̲e̲q̲u̲e̲s̲t̲ ̲t̲o̲ ̲r̲e̲c̲e̲i̲v̲e̲:̲ In the protocol
MSV1 one of the connected stations obtains the status
of a control station (in most cases the host computer).
Hence all other stations are tributary stations, which
can only exchange data with the control station. Only
the control station can initiate data transmission by
issuing time sequenced requests to send or to receive
(polling and selecting) to the other stations. The selection
of a specific station as well as the selection of a data
source or sink within that station is accomplished via
address characters which are contained in the request.
Hence a tributary station can only send text if it recognizes
its address during receipt of a request to send and thus
becomes the master station. The receipt of EOT resets
the tributary stations to be ready to receive requests
to send or to receive.
F̲l̲o̲w̲c̲h̲a̲r̲t̲s̲ ̲f̲o̲r̲ ̲t̲h̲e̲ ̲p̲r̲o̲t̲o̲c̲o̲l̲ ̲p̲h̲a̲s̲e̲ ̲"̲r̲e̲q̲u̲e̲s̲t̲ ̲t̲o̲ ̲s̲e̲n̲d̲"̲ ̲a̲n̲d̲
̲"̲r̲e̲q̲u̲e̲s̲t̲ ̲t̲o̲ ̲r̲e̲c̲e̲i̲v̲e̲"̲
Control station Tributary station Control station sends
(host computer) (DSt) sends
sends
Request to send Phase Text
Transmission
---EOT---ADE/ENQ STX/ESC/ADR/..Text 1../ETB/BCC --------ACK 1-----
EOT---No text
DSt available next
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲:̲ No reaction
ADE/ENQ---------------------------------------------EOT---next
DSt!
Repeat max. 4 times
Request to receive Phase
Text
Transmission
---EOT---ADA/ENQ--------ACK 0---------------------STX/ESC/ADR/..Text
1..
ETB/BCC
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲s̲:̲-------------T 1-------------------------
-----ACK 0---------------------------EO…0e…T…0f…--ADA/ENQ-
-----ACK 1--------------------- Terminate or abort
data transmission
-----WABT---------------------- Next DSt!
-----NAK-----------------------
ADA/ENQ
Corrupted character sequences have been marked by cansellation!
ADE . A̲ddress of tributary station and input device
ADA . A̲ddress of tributary station and output device
ADR . A̲ddress of input device only if required!
T̲e̲x̲t̲ ̲t̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲:̲ After selection of a station by request, the text
is transmitted in the message formats above. Error free text blocks
are positively acknowledged. Positive acknowledgements are numbered
(ACKO, ACK1) in order to avoid losses of blocks.
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲s̲:̲ Corrupted text characters cause negative acknowledgement
(NAK) from the receiver. The sender re-transmits the erroneous text
block. In case of corrupted data transmission control characters the
sender does not receive any acknowledgement or it receives a corrupted
acknowledgement. After expiration of the time-out T1 = 3 sec the sender
repeatedly requests retransmission of the acknowledgement (by means
of ENQ).
T̲e̲r̲m̲i̲n̲a̲t̲i̲o̲n̲:̲ After transmission of text the master station (sender)
terminates with EOT. Transmission is also terminated if no positive
acknowledgement is received after repeated retransmission of the text.
F̲l̲o̲w̲c̲h̲a̲r̲t̲ ̲f̲o̲r̲ ̲t̲h̲e̲ ̲p̲r̲o̲t̲o̲c̲o̲l̲ ̲p̲h̲a̲s̲e̲ ̲"̲t̲e̲x̲t̲ ̲t̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲"̲ ̲a̲n̲d̲
̲"̲t̲e̲r̲m̲i̲n̲a̲t̲i̲o̲n̲"̲
Master station sends Receiver Master sta-
sends tion sends
Transmission of text in
m̲u̲l̲t̲i̲p̲l̲e̲ blocks
STX/ESC/ADR…0e…*…0f…/..Text../ETB/BCC
ACK 1
STX/..Text..ETB/BCC ACK 0
0
STX/..Text..ETX/BCC ACK 1 EOT
Transmission of text
in o̲n̲e̲ block:
STX/ESC/ADR…0e…*…0f…/..Text 1../ETX/BCC ACK 1 EOT
Transmission of m̲u̲l̲t̲i̲p̲l̲e̲ texts in m̲u̲l̲t̲i̲p̲l̲e̲ blocks:
STX/ESC/ADR…0e…*…0f…/..Text 1..ETX/BCC ACK 1
STX/..Text 2../ETX/BCC ACK 0
STX/..Text n../ETX/BCC ACK 0 EOT
1
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲s̲:̲ Receiver
sends
STX/ESC/ADR/..Text../ETB/BCC NAK STX/...
Retransmis-
sion of block
STX/ESC/ADR/..Text 1../ETB/BCC ACK 1 ENQ…0e…**…0f… ACK
1
STX/ESC/ADR/..Text 1../ETB/BCC ENQ…0e…**…0f… wrong
ACK
0
T1
STX/ESC/ADR/..Text 1../ETB/BCC
STX/ESC/ADR/..Text 1../ETB//BCC ENQ…0e…**…0f… NAK
T1
STX/ESC/ADR/..Text 1../ETB/BCC
STX/ESC/ADR/..Te.. EOT
T1 (T4)
Station becomes "not
ready"
Corrupted characters resp. character sequences are marked
by cancellation! The protocol MSV 1 takes into account
all rules for the "Basic mode" which have been layed down
in the ECMA-16, ECMA-24 and ISO DR 1745 standards.
** This request for acknowledgement
is repeatedly issued in case
of erronous responses, finally
transmission is terminated
with EOT.
* If required address
(station, I/O-Device)
ADR in 1st text
block.
F̲l̲o̲w̲c̲h̲a̲r̲t̲s̲ ̲f̲o̲r̲ ̲t̲h̲e̲ ̲p̲r̲o̲t̲o̲c̲o̲l̲ ̲p̲h̲a̲s̲e̲ ̲"̲r̲e̲q̲u̲e̲s̲t̲ ̲t̲o̲ ̲s̲e̲n̲d̲"̲ ̲a̲n̲d̲
̲"̲r̲e̲q̲u̲e̲s̲t̲ ̲t̲o̲ ̲r̲e̲c̲e̲i̲v̲e̲"̲
Control station Tributary station Control station sends
(host computer) (DSt) sends
sends
Request to send Phase Text
Transmission
---EOT---ADE/ENQ STX/ESC/ADR/..Text 1../ETB/BCC --------ACK 1-----
EOT---No text
DSt available next
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲:̲ No reaction
ADE/ENQ---------------------------------------------EOT---next
DSt!
Repeat max. 4 times
Request to receive Phase
Text
Transmission
---EOT---ADA/ENQ--------ACK 0---------------------STX/ESC/ADR/..Text
1..
ETB/BCC
E̲r̲r̲o̲r̲ ̲c̲a̲s̲e̲s̲:̲-------------T 1-------------------------
-----ACK 0---------------------------EO…0e…T…0f…--ADA/ENQ-
-----ACK 1--------------------- Terminate or abort
data transmission
-----WABT---------------------- Next DSt!
-----NAK-----------------------
ADA/ENQ
Corrupted character sequences have been marked by cansellation!
ADE . A̲ddress of tributary station and input device
ADA . A̲ddress of tributary station and output device
ADR . A̲ddress of input device only if required!
