Code-conversion operations
Source-program information
Groups of short messages
Object-program information
Encrypted data
Unedited information
Transparency is provided as a standard feature for EBCDIC and SBT. It is optionally available for USASCn. Transmission-Code Checking
The error-detection circuitry for each transmission
code is incorporated in the synchronous equipment.
Automatic-checking capability is provided for the
three transmission codes; however the checking
method employed depends on the Synchronous Ter­
minal Control and the kind of transparency chosen.
Table II indicates the checking methods available.
Table II. Transmission-Code Checking
Type of Checking
Transmission
No Transparency
Code
T ransparenc y Installed and Installed Operating EBCDIC CRC-16 CRC-16 USASCII VRC/LRC CRC-16 SBT CRC-12 CRC-12
CRC = Cycl ic Redundancy check
VRC = Vertical Redundancy check
LRC = Longitudinal Redundancy check
Transparency I nstalled But
Not Operating
CRC-16
VRC/CRC-16
CRC-12
VRC/LRC. This transmission-error-detection
method consists of a combination of the vertical
redundancy check (VRC) and longitudinal redundancy
check (LRC). Thus, an odd VRC parity check is
performed on each transmitted character including
the LRC character. The LRC check is an even
longitudinal check on the total data bits (not in­
cluding parity) of the transmitted block of characters
comprising the message block. The LRC is accumu­
lated at both the sending station and the receiving
station during the block transmission. This accu­
mulated value becomes the block-check character
(bcc). The trans mitted bcc is automatically
compared after ETX, ETB, or ITB with the bcc
accumulated at the receiving station for an equal
condition signifying correct receipt of the trans­
mitted block.
VRC/ CRC. This transmission-error-detection
method consists of a combination of a vertical
redundancy check and a cyclic redundancy check
(CRC). The CRC checking makes use of a circuit­
implemented polynominal that treats the transmitted
message as a binary nU!llber, and performs modulo
2 divide operations on this binary number (carries
are not considered). Both the sending and the recei­
ving stations generate this value individually. The
transmitting station sends its generated value
resulting from the modulo 2 division. Only the
remainder is transmitted to the receiving station, at
which point the two CRe values are compared. Equal
comparison indicates accurate transmission.
CRC. This checking method, as outlined above, be used in place of the other listed checking methods.
The two variations of the polynominal (CRC16 and
CRC12 for eight-bit and six-bit codes respectively)
are included in the publication, General Information-­
Binary Synchronous Communications, Form A27 -3004. Synchronous Bases
Three versions of Synchronous Bases are available: • Synchronous Base IA accommodates EBCDIC
or USASCII at speeds up to 2400 bps. • Synchronous Base IB accommodates SBT, USASCII, or EBCDIC at speeds up to 2400 bps. • Synchronous Base 2A accommodates EBCDIC or USASCII at speeds up to 4800 bps.
Synchronous Base 1A permits the attachment of up
to 24 lines using EBCDIC or USASCII terminal con­
trols and operating at bit rates not exceeding 2400 bits per second. This provides a character rate of
up to 300 characters per second [(2400/8) = 300 characters]. Up to 600 digits per second can be
transmitted in packed-decimal.
Synchronous Base 1B permits the attachment of up
to 16 lines using EBCDIC, USASCII, or SBT terminal controls and operating at bit rates not
exceeding 2400 bits per second. This provides a
character rate of up to 400 characters per second
[ (2400/6) = 400 characters] for SBT operation.
Synchronous Base 2A permits the attachment of up
to 12 lines using EBCDIC or USASCII terminal con­
trol and operating up to 4800 bps. This provides a
character rate of up to 600 characters per second (4800/8) = 600 characters or up to 1200 digits per
second in packed decimal.
Synchronous Line Set Synchronous communications facilities are attached
to the 2703, modular by four, via a Synchronous
Line Set. Each line set services up to four facilities
(half- or full-duplex). The maximum number of line
sets per Synchronous Base I depends on the trans-
mission code employed and whether the Synchronous
Clock feature is provided.
53

These line sets provide for the attachment of up
to four data sets. The following data sets, or
equi valent, can be attached via the Synchronous
Line Set without a Synchronolls Clock Western Electric Data Set 201A3 (2000 bps)
Western Electric Data Set 201B1 (2400 bps)
Synchronous Clock Feature. This feature is sup­
plementary to the Synchronous Line Set and provides
for the attachment or up to four data sets (or IBM
Line Adapters), where clocking for bit synchroni­
zation is not provided by the data set (or line
adapter). This feature requires the installation of
synchronous line speeds (see "Synchronous Line Speed Option"), and accommodates the following
data sets (modems) or their equivalent:
IBM 3977 Modem (WTC only)
IBM 3976 Model 3 (WTC only) GPO Datel 1 Model 5 (WTC only)
NTT DT1203 (WTC only) PTT D1200S (WTC only) PTT GH2002 (WTC only--Model has an optional
clock. Either the modem clock or the machine
clock feature may be used, but not both; nor
can both be intrrmixed on the same communi­
cations facility.)
Western Electric Data Set 202C1 Western Electric Data Set 202D1 Table III summarizes the number of synchronous
lines that can. be attached per 2703 by Synchronous Base.
Synchronous Line Speed Option These options provide the pulses to drive the Synch­ ronous Clock feature, which is required whenever
the data set or line adapter does not provide timing
or clocking pulses needed for external bit sampling.
The Synchronous Line Speed Option is available for
operation of the SF at 600, 1200, 2000, or 2400 bits
per second for World Trade Corporation applications
and at 1200 bps for domestic use. Only one speed
can be specified per Synchronous Line Set, and this
speed is preset. If the Synchronous Clock feature is
specified for one line, the other station(s) on the net­
work serviced by this line must have the Synchronous Clock feature installed, and all stations must have
the same bit rate.
Data Set (Modem) Features
A variety of transmission facilities can be attached
to the BSC -adapted 2703, depending on the type
facility used, transmission configuration, trans-
mission speed employed, country of use, and so
forth. Refer to Figure 13 for details.
54
Table m. Synchronous Line Sets Synchronous Transmission Number of Number of
Base Code Synchronous Synchronous
Line Sets Line Sets without Yi,.ith Syn- Synchronous chronous Clock Clock Base Mach. Base Mach.
1A EBCDIC, 6 12 3 6
2A USASCn 3 6 IB SBT 4 8 3 6 Station -Selection Feature
The Synchronous Features in a 2703 may be opera­
tionally used as the BSC portion of a master station,
or the SF may be used in a BSC-equipped multi­
point network as a tributary (remote) station. The
basic synchronous-equipped 2703 is designed to
operate as a master station on a point-to-point
basis; however, with the installation of the Station­ Selection feature, a synchronous-equipped 2703 can
be used as the tributary station--thus permitting a
number of low-traffic-volume stations to be effec­
tively combined to fully utilize the throughput capa­
bility of a multipoint line.
A multipoint network could typically be configured
as shown in Figure 14.
The Station-Selection feature causes the elimina­
tion of interference that would otherwise be caused
by interstation transmission on the line. Thus, the CPU (with a 2703 containing Station-Selection­ adapted SF) is interrupted only when the SF's selec­
tion or polling address is received and transferred
to main storage, at which point main storage can be
interrogated for proper programmed action.
The Station-Selection feature is required when the SF is attached to a multipoint network and the station
is operating as a remote (tributary) station and all
transmission operations are directed to or from the
central (master) station. BSC-adapted stations can operate on the same
multipoint line. provided they:
1. All use the same transmission code;
2. All utilize the same checking features;
3. All are able to handle, if not employ, the same
optional features and special operations re­
specting their compatibility supplements: ,1. All operate at the same line speed.
The Station-Selection feature implements two
additional commands: Address Prepare (Adprep),
and Search.