Teletype 33 General Description And Operation

TELETYPE CORPORATION
Skokie, Illinois, U.S.A.
SECTION 574-123-l00TC
Issue 3, June 197 4
33 CALL CONTROL UNIT
GENERAL DESCRIPTION
AND OPERATION
CONTENTS
PAGE
1.
GENERAL
.....
.
. .
..
. . .
.
1
2.
DESCRIPTION AND
OPERATION
....
. . .
. .
1
CALL CONTROL UNIT
FOR SWITCHED NETWORK
SERVICE ...........
1
CALL CONTROL UNIT FOR
PRIVATE WIRE SERVICE ..
8
1. GENERAL
1.01 This section provides a general
description and operation of the 33 call
control units. It is reissued to consolidate 33
information. Marginal arrows are not used to
indicate changes.
1.02 This section describes two call control
units which may be considered basic
units. They are:
(1) Call Control Unit for Switched Net-
work Service
(2) Call Control Unit for Private Wire
Service.
1.03 The call control unit is the electrical
link which joins the various compo-
nents of the set to one another, and the set to the
transmission facilities.
1.04 References to left, right, front, or rear
consider the call control unit as viewed
by the operator.
1.05 This equipment is intendecl. to be oper-
ated in a room environment within the
temperature range of 40° F to 110° F. Serious
damage to it could result if this range is exceeded.
In this connection, particular caution should be
exercised in using acoustical or other enclosures.
2. DESCRIPTION AND OPERATION
CALL CONTROL UNIT FOR SWITCHED NET-
WORK SERVICE
2.01 The call control unit for Switched
Network Service (Figure 1) supplies de
signals to a data set. The data set modulates these
signals into tone frequencies which are trans-
mitted over the telephone lines. A data set at the
receiving station demodulates the tone fre-
quencies back to de signals which are then
handled by the call control unit for operation of
the teletypewriter set. For a better understanding
of the call control unit, 2.02 briefly describes the
data set.
2.02 Start-stop de signal pulses form essen-
tially a square wave which cannot
readily be transmitted over telephone lines. The
data set is basically a converter which changes the
de signals from the sending or calling station into
frequency-shifted tones for transmission over the
telephone network. A marking pulse from a
sending station is converted to a 1270-hertz
marking signal _(Fl mark) and a spacing pulse
becomes a 1070-hertz spacing signal (Fl space).
The data set at the receiving or called station
sends a 2225-hertz marking signal (F2 mark) and
a 2025-hertz spacing signal (F2 space). During
transmission of a message, the calling station
sends a mark and space tones (Fl mark and
space) while the called station sends a continuous
mark tone (F2 mark). In this way the telephone
facilities are operated on a full duplex basis.
If
the
signal received at either station (Fl mark and
space at the called station and F2 mark at the
calling station) shifts to a space tone for more
than one second, or if the received signal is lost
for one second, the data set will cause the station
to be disconnected. This provides assurance that
the connection is maintained for the entire period
of message transmission.
2.03 The call control unit used with the data
set operates with conventional tele-
phone central offices that have the necessary
©
1962, 1964, 1969, and 1971 by Teletype Corporation
All rights reserved
Page 1
Printed in U.S.A.