The
bit configuration
of
the hold character
is:
sTART
CBA
8 4 2 STOP
ee
20 070 ll 0
Reactivation
Message:
This message
informs
the
data
processing
center
that
one of the
four telegraph
units
(the
one designated
by the
low-speed
unit
selector)
is
ready to
receive output
massages.
The
format
of
this message
is:
Reset
character,
TIC,,
telegraph
unit
address,
EOMpy,
reset
character
This message
is initiated
manually
by pushing
the
start
key.
Reset
Character:
The reset
character
is sent
by the
oca
immediately
after
the operator
presses
the start
key;
it also is sent
automatically
between data
messages
when
the oca
is ready for
the next message;
finally,
it
is sent whenever
a
validity error
occurs.
The bit
configuration
of the
reset character
is:
sTART
CBA8421
= sTOP
1
tA
le le 0
i
1
OUTPUT
MESSAGES
Output
messages
contain data
to be
sent to
the tele-
graph
units.
Incomplete
Message:
This is one
in which
no tele-
graph
end-of-message
sequence
is
contained
in the
body
of the
message.
Its format
is:
Telegraph
unit
address,
body of message
(95
characters
), EOMpx*
*zoMps
is not sent to
the telegraph unit.
Complete
Message:
The
telegraph end-of-message
sequence
is
contained
in the body
of this message.
Its
format
is:
Telegraph
unit
address, body (maximum
of 95
characters
), EOMc*
*EOMo
is dropped in
the oca. The telegraph
end-of-mes-
sage
sequence, however,
is included in
the body of the
message.
32
Output
Communication
Adapter
Operator’s
Panel
This
panel
(Figure
30)
is used
to control
the oca
and
to
place it
in normal
operating
condition.
The
switches,
keys,
and lights,
and their functions
are:
Power
Off/On:
This
switch
controls
the Ac
power.
It
must be
in the
on position
for normal
operation.
Start:
Depressing
this key
resets the
oca so
that it
is
able to
receive
an output
message
and
operate
nor-
mally.
It also
causes
the input
message
control
to
send
the
reactivation
message
to the
data processing
center,
signaling
the data
processing
center
that
the telegraph
unit
specified
by
the low-speed
unit selector
is
ready
to
receive
messages.
Stop:
Depressing
this
key stops
all
operations
of
oca.
If
a message
is
being transferred
to
the telegraph
equipment,
however,
data
transfer
is not
stopped
until
a
complete
message
has been
sent.
Tape
Feed:
Pushing
this
key
causes
a letters
shift
character
to be sent
to the
selected
telegraph
unit.
This
key
is effective
only when
no output
message
is being
transferred.
Low-Speed
Unit
Selector:
This
multiple-position
switch
allows
the
operator
to select
one of
the four
telegraph
units.
Selecting
a unit
is always
followed
by
either
pushing
the start
key to reactivate
the
unit, or
pushing
the tape
feed key
to send
a letters
shift
char-
acter
to
the unit.
Power
On:
This
light indicates
that
ac power
is
present
in
the oca.
System
Available:
This light
is normally
on.
It sig-
nifies
that the
9000 series
system is
available.
Punch
Check:
This
light indicates
that
an alarm
condition
exists in
one of the
telegraph
units.
An 18M
9000 Series
Airlines
Reservation
System
is
interwoven
with common
carrier
service
in three
gen-
eral areas:
(1) The
common carrier
bears
messages
at 2,000 bits per
second on
full-duplex lines
between
the data processing center
and the terminal inter-
changes. (2) If the
agents’ sets are located
farther than
1,500 feet from their terminal interchanges, a common
carrier service carries the messages over these dis-
tances, at approximately 74 or 148 bits per second on
full-duplex lines. (3) A common carrier telegraph net-
work system may feed into and receive from the 1BM
9000 series system either through the input and output
communication adapters or
by direct connection with
the terminal interchanges at speeds up to 100 telegraph
words per minute.
At every point where the Airlines
Reservation System
data and control signals enter
or leave a common car-
rier service, they must pass
through a common carrier
data set. Depending upon
the speed, distance, and
complexity of the transmission,
the data set may need
to modulate, demodulate (or both), act as a special
connector, or consist of a demarcation strip.
The specifications for the low-speed data sets re-
quired for the most remote areas of a 9000 series
Single Interchange Sharing at the Same Location
Common Carrier Services
system must be decided by
the individual airline to
conform to particular system plans and common carrier
service. The predetermined specifications for data sets
located between agent sets and the terminal inter-
changes are that they be full-duplex
sets, able to carry
approximately 74 or 148
bits per second. Variable
factors in determining these
data sets include the dis-
tance of transmission, need or lack of need for modula-
tion, preference as to type of
modulation and demodu-
lation, and availability of differing
types of service at
the geographic locations involved.
The specifications for the higher-speed data sets
located at the data processing center and at every
terminal interchange connection with the main trunk
lines are given in the Electronic Industries Associa-
tion’s Recommended Standards 232. These sets must
handle at least 2,000 bits per second on a full-duplex
basis. They must both modulate and demodulate. At
the data processing center, each data set consists of a
modulation unit attached to the output line and a
demodulation unit for the input line. The possible
arrangements for data sets at the terminal-interchange
connections
to the trunk lines are shown in Figure 31.
Single Interchange
(N = 30)
Interchange 1 Interchange 2 Interchange 3 Interchange N
Output
Input Output | Input Output | Input Output | Input
Msgs Msgs Msgs Msgs Msgs Msgs Msgs Msgs
A
Demod Mod Demod Mod Demod Mod Demod Mod Demod Mod
Data Set* Data Set* Data Set* Data Set* Data Set*
Input
Output
on
to Data Proc-
essing Center
*2,000-bits-per-second data set
—~ >
Figure 31. Arrangements of High-Speed
Data Sets and Terminal Interchanges
Common Carrier Services 33
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