1970s Technical Control

8/9/2019 1970s Technical Control

1/6

1970s Technical Control

A data Communication Historical Series

By Bob Pollard

Technical Control (T C or Tech. Control)The term Technical Control is a military designation for facilities (line, circuit, and channel) termination

equipment, MODEM(s), jacks and patch panels, and all the necessary test and control equipment. Similarequipment is used in the private sector, and therefore, a discussion of one will describe the other. esternUnion maintenance personnel would refer to a Technical Control facility as a Wire and Repeater Center(room).

Typical 1940s Western Union Telegraph test and switch board

Most military T C facilities are associated with a large message-switching center. In the private sector,such as Western union, the Wire and Repeater rooms (centers) are located in most large cities withinterconnecting trunk lines between cities and the local circuits terminate into the closest Wire andRepeater room. The military uses Crypto equipment for data security purposes and again the privatesector utilizes similar equipment for scrambling and decoding the data bit stream.

A Tech Control facility would have the necessary equipment to perform the following functions:

A cable connection (cross cut mainframe) facility for connecting outside local or distant lines(circuits) to the internal equipment interfaces.
http://sites.google.com/site/mdprcp/TC-1A.jpg?attredirects=0


2/6

Jack Matrix for line and equipment testing and rerouting of failed lines and equipment.

MODEM and other Device racks for mounting the required MODEM(s) and devices.

Crypto interface facilities. The Crypto equipment would be located in a high security area.

Cable connection Mainframe:The cable connection mainframe would normally be located in the general area of the T C. The

mainframe is the point where all connections between the outside terminal equipment and lines fromdistant points are connected to the internal T C and center equipment. Each outside line enters thebuilding via a cable from the Communications Company (Telephone / Vendor Company) and eachindividual line is terminated at the mainframe on an assigned terminal block connection(s). The T C hastest and patching jack sets assigned to each line, and these are also terminated on a terminal blockconnection(s). Wire straps are then connected between the line terminal blocks and the appropriate jacksets in T C. MODEM(s) are handled in a similar manner. They are assigned jack sets in T C that areassociated with particular pre-assigned lines. This is accomplished via straps on the terminal block(s). Asecure cable facility is routed between T C and Crypto.Technical Control facility:The technical Control facility consists of many panels of jacks (plug-in jacks) that are individuallyassociated with a line or piece of equipment. A line and associated MODEM would have jacks next toeach other. The jacks are internally wired (connected) so the line and MODEM are normally connected toeach other. This normal connection could be broken if a patch cord was inserted into the jack. The patchcord will break the original connection and route the circuit through the patch cord. The other end of thepatch cord would be inserted into a substitute equipment/line jack. This allows for substitution of failedlines or equipment by patching a good line in place of a failed line or a failed MODEM could be replacedby a good one via a patch cord. Other associated jacks provide a means of testing lines and equipmentwithout breaking the connection between the line and MODEM.

In addition to the jack matrices Tech Control has many switches, meters, patch cords and thenecessary test equipment to trouble-shoot failed lines and equipment. Different patch cords are used thatallow flexibility for testing or connecting equipment together. For example: a black cord connects a 2-wirecircuit directly, jack tip to tip and jack ring to ring. A red cord reverses the connection, tip to ring and ringto tip. This reversal allows equipment to be connected back to back. In other words the DC side of aMODEM could be connected to the DC side of another MODEM. This connection reversal connects the

send leg of one MODEM to the receive leg of another MODEM and in the reverse direction receive leg tothe send leg. This referred to as a bust back or back to back connection.This back to back connection is done to test the line and/or MODEM(s) or extend a line. In a test mode,full duplex line, any data transmitted by the distant end is routed back to them because the receivedsignal is patched to be sent back on the other MODEM, which is the distant end receive line. This type ofpatch could also be used to extend a line (cut through) to another office.Jacks and patch cords:Figure 1 illustrates how individual jacks are connected to the send and receive side of a Carrier device, amultiplex unit, a tuner, an amplifier or pad (power reducer) and the send and receive lines, which aretelephone channels; two individual telephone channels, one for send (2 wires) and one for receiving (2wires), are required. Since the Carrier, multiplex unit (modulator or demodulator) and frequency tuner are

connected to telephone lines an amplifier is used on the Carrier receiving line because the power level is17 dB lower than the normal Carrier operating power level. On the send side to the telephone line thepower level would be reduced 17 dB. This power level change is necessary when the connection is to atelephone line. The tuner and modulator are necessary because the Carrier device is functioning on a subchannel, a small frequency portion of the total available telephone channel bandwidth (usable 3300-hertz).The sub band (individual) frequency is generated through the combined Carrier device modulatorand tuner, which means the telephone channel, does not provide the analog signal (frequency or power.

The Carrier device is used for discussion since it requires many jacks to serve all the necessaryfunctions and test facilities, which illustrates how complex a jack matrix can be for some devices. The


3/6

MODEM device does not require the same number of jacks since the power amplifier, receive side, andpad (power reducer), send side, are not used. Also the modulator / demodulator and tuner sections areelectrically combined in a different manner.

The following is a component description of Figure 1. The subject jacks would be located adjacent toeach other within the total panel of jacks.

1. The frequency tuner, which is necessary for modulation or demodulation of the carrier frequency. 1A is partof the tuner.2. The carrier frequency (oscillator) for the modulator or demodulator.3. On the receive side, to the carrier device, this would be a power amplifier.4. On the send side, from the carrier device, this would be a pad (power reducer).5. The jack connected to the carrier device for transmitting (send) to the telephone line.6. The jack connected to the carrier device for receiving from the telephone line.7. The jack connected to the frequency tuner on the transmitting (send) line and strapped to jack 5 to completethe circuit.8. The jack connected to the frequency tuner (1A) on the receive line and is strapped to jack 6 (to receivecarrier) to complete the circuit.9. The jack connected to the frequency tuner on the telephone channel side and is strapped to jack 10 tocomplete the circuit.10. Jack 10 is connected to the amplifier (3) on the receiving side of the line. On the send (transmitting) side of

the line jack 10 is connected to a pad (power reducer) (4). Jack 10 is strapped to jack 9 to complete the circuit.11. Jack 11 is connected to the amplifier (3) on the receiving side or the pad (4) on the send side. Jack 11 isstrapped to jack 12 to complete the circuit.12. Jack 12 is connected to the telephone channel (line), one for sending and a second one for receiving sincesending and receiving functions must be separated, which requires two channels (lines). Jack 12 is strapped to

jack 11 to complete the circuit.13. Jack 13 is a jack used for connecting test equipment; includes an isolation pad (coil).

Figure 1

The patch cords used to plug into these jacks use a tip and ring that makes contact with the twohalves of the jack and breaks the internal jack strapped connections. The two halves are necessary sincethe circuit (line) uses two wires all the way from the carrier device to the telephone channel, which alsouses two wires. There would be two wires for sending and two wires for receiving, making a total of four

wires utilized from end to end for a full duplex circuit.

Patch cords are used for replacing faulty equipment, rerouting a line or for test purposes. If a patch cordwas plugged into jack 5 (send) the connection would be broken between jack 5 and jack 7, which woulddisconnect the Carrier device from the tuner. The open end of the patch cord could then be plugged intodifferent tuner (another jack 7), which would result in a replacement of the original tuner. The other side ofthe replacement tuner would have to be patched into the original line on the pad side, using the jacksrepresented by 9 (replacement tuner) and 10 the original pad connection. The end result would be apatch cord between jack 5 (original Carrier) and a jack 7 (replacement tuner) and a patch cord between a
http://sites.google.com/site/mdprcp/TC-2.tif/TC-2-full;init:.tif


4/6

jack 9 (replacement tuner) and jack 10 of the original pad, which is connected to the original telephonechannel.

There are different types of patch cords, such as a three-wire patch cord that would be used in jacksthat are connected to three circuits for various reasons. The patch cord and jack would use tip, ring andsleeve connections. The red patch cord (reversed) was covered earlier.

Figure 2 shows one end of a black patch cord; the other end would be duplicated.

Figure 2Figure 3 shows a typical T C service and control console.

Figure 3

Figure 4 shows several racks of Jack Panels, with patch cords plugged into several jacks and hangingbelow the jacks.A Technical Control can be a fairly simple arrangement of patch panels, racks of MODEM(s) and other

equipment, a cabling mainframe, test equipment and a monitor and control console. Or a Tech. Controlcan be an automated very sophisticated facility.
http://sites.google.com/site/mdprcp/TC-4.jpg?attredirects=0http://sites.google.com/site/mdprcp/TC-3.tif/TC-3-full;init:.tif


5/6

Figure 4

In the 1980s and into 2000 most large message switching centers had large T C facilities. But, due tothe proliferation of the Internet, large message (data) switching centers were phased out during the1990s and early 2000s since it was more economical to use the world wide communication facilitiesoffered by the WWW / Internet. This eliminated many T C facilities on military bases and in the privatesector. The Internet Routers (super computers) would now be the strategically located message (data)routing systems. The Router facilities use a similar more modernized type of automated testing, circuitrerouting and control facility.

CRYPTO:When encryption devices are used messages (data) are encrypted during transmission before enteringthe DC side of the MODEM and are decrypted at the receiving end on the DC side of the MODEM. Thisencrypted and decrypted data is routed through the jack matrices of Tech. Control.

A typical Terminal to Terminal communication via a data/message Switching Center would occur and beconnected as illustrated in Figure 5, a simple sequence; all connections are routed through the T C jackpanel matrix. A review of Figure 19-6A and Figure 19-6B will provide a more complete picture of theactual path a data signal would take.Terminal (send) > > > CRYPTO (encryption) > > > (DC) MODEM (AC) > > >Telephone line or leased line> > > (AC) MODEM (DC) > > > CRYPTO (decryption) > > > Communications switching Computer > > >CRYPTO (encryption) > > >(DC) MODEM (AC) > > > Telephone line or leased line > > > (AC) MODEM(DC) > > > CRYPTO (decryption) > > > Terminal (receive).

Figure 5

Figure 6 illustrates how a 1970s through 1990s automated Tech Control would be configured and the types ofequipment that would be used.
http://sites.google.com/site/mdprcp/TC-5.jpg?attredirects=0


6/6
http://sites.google.com/site/mdprcp/TC-6.tif?attredirects=0

Documents

1970s Technical Control