Voice alarm signalling system

Voice and alarm signalling capability between supervisory personnel at monitor and control sites located at separated transceiver facilities of a (repeatered) multichannel communication network is provided by a multichannel multiplexed encode/decode scheme in which voice and/or alarm signals generated at one station are digitally encoded and formatted so as to be inserted into the data stream of the normally conveyed data traffic over the active channels of the network. At the receiving terminal site, these inserted signals are removed from the high data rate digital data stream and delivered to decoding equipment which reconstructs the original voice and/or alarm signals for delivery to the audio equipment of station operation personnel. The encoded signals are inserted as overhead bits for each active channel, so that a fault on one channel will not prevent the completion of trasmission of the intended communication between terminal site personnel.

FIELD OF THE INVENTION 
The present invention relates to communication systems and is particularly 
directed to a scheme for encoding and decoding voice and alarm signals 
used for network supervisory purposes in a repeatered, multi-channel 
communication network. 
BACKGROUND OF THE INVENTION 
In copending application Ser. No. 149,291, filed May 12, 1980 by P. Casper 
et al entitled Repeatered, Multi-Channel Fiber Optic Communication Network 
Having Fault Isolation System, assigned to the assignee of the present 
application, there is described a high data rate digital signalling 
environment wherein the transmission of high density signalling traffic, 
such as T-4 telephone trunk voice signals and data, is carried out over a 
plurality of fiber optic transmission channels between geographically 
relatively remote signal interfacing terminal stations. The terminal 
stations may be coupled to receive the signals to be transmitted from 
trunk interface port connections, microwave interface equipment, etc., and 
include electro-optic transceiver equipment for coupling multi-megabit 
digital data signals over a fiber optic communication network. At these 
stations processor-based control equipment is provided which serves to 
perform control and monitoring functions that govern the overall operation 
of the network. As is explained in the above-referenced application, the 
network includes protection equipment that serves to maximize the 
integrity of each channel, the protection equipment being substituted in 
place of a normally used fiber optic link in the event of unacceptable 
signal degradation or channel failure. The control and operation of this 
protection equipment as well as the control and operation of other 
portions of the system may be effected internally by way of the 
processor-based monitor and control equipment. These actions may also be 
carried out externally through operator intervention, by-passing an 
internally programmed control sequence when necessary. 
Of course, as will be readily appreciated by those skilled in the art, it 
is common practice in sophisticated communication networks to employ 
operator command consoles through which monitor and control actions may be 
effected. In an environment where separate and remote facilities are 
provided for this purpose, such as in the environment of the network 
described in the above-identified application, some means of providing a 
signalling link, preferably a voice link, between the station operators is 
required in order that system supervisory personnel can communicate 
directly with each other and take whatever effective action is necessary 
to enable the network to perform as intended. 
A common expedient for providing this voice signalling capability is a 
conventional telephone communication system through which the network 
operators call one another just as do other subscribers of the system. 
Unfortunately, this approach subjects the intended voice link between 
stations to the performance of the external telephone equipment, including 
circuit availability and channel integrity. In a fiber optic communication 
network such as that described in the above-referenced application, a 
major feature of the network is its use for conveying high density 
telephone trunk traffic between relatively remote stations over a 
plurality of fiber optic channels. If, in such a network, voice 
communications between station operators were to be conducted through 
external telephone equipment whose signals, in turn, were formatted for 
transmission over the very network being monitored and controlled by the 
station operators, it can be seen that serious consequences could result 
from a fault on the channel over which the voice signals for 
operator-to-operator communications were being conducted. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, voice and alarm signalling 
capability between supervisory personnel at monitor and control sites 
located at the separated transceiver facilities of a (repeatered) 
multichannel communication network is provided by a multichannel 
multiplexed encode/decode scheme in which voice and/or alarm signals 
generated at one station are digitally encoded and formatted so as to be 
inserted into the data stream of the normally conveyed data traffic over 
the active channels of the network. These encoded signals are generated at 
a data rate considerably less than that of the high data rate signals 
conveyed by the network and are inserted (multiplexed) periodically as 
auxiliary or overhead data bits in the digital data stream of each active 
channel of the network. At the receiving terminal site, these overhead 
bits are demultiplexed from the high data rate digital data stream and 
delivered to decoding equipment which reconstructs the original voice 
and/or alarm signals for delivery to the audio equipment of station 
operation personnel. Because the encoded signals are inserted as overhead 
bits for each active channel, a fault on one channel will not prevent the 
completion of transmission of the intended communication between terminal 
site personnel. Moreover, by having redundant access to all of the 
channels over which the telephone traffic conveyed by the network is 
serviced, station operation personnel have the capability of monitoring 
the "ear-input" quality of the voice signals heard by the subscribers of 
the network. 
In order to implement the required encoding and decoding functions for 
interfacing voice/alarm signals with the data traffic handled by each 
network channel, the system according to the present invention employs a 
voice/alarm interface module at each terminal site where network operation 
personnel monitor and supervise network performance. Each of these modules 
is coupled to receive and accept signals produced from a conventional 
telephone handset, such as dial pulses and voice signals, and includes 
tone signalling circuitry that generates a pair of tones to be used for 
station address signalling, and analog voice coupling circuits for voice 
signalling. The analog signals (dual tone or voice) are digitized via a 
companding A-D converter and formatted for delivery to the transceiver 
equipment inserted with each channel of the network for transmission as 
prescribed overhead bits of each active channel. 
Each module also contains deformatting and D-A conversion circuitry which 
receives the serial overhead bits from any selected one of the active 
channels and reconstructs the original analog signals for delivery to the 
audio equipment of the terminal station. Part of each module is configured 
to detect station address signals, such as those produced by rotary dial, 
key tone, etc., signalling units. Station address and alarm signalling is 
effected through the use of the above-mentioned dual tone pair, the 
frequencies of which are chosen to prevent tone detection circuitry in the 
module from detecting voice inputs as address or alarm signals.

DETAILED DESCRIPTION 
As was mentioned briefly above the present invention has particular utility 
in a repeatered, multichannel fiber optic communication network such as 
that described in the above-referenced application. However, it should be 
understood that the invention is not limited to such an environment but 
has application to the signalling links where data may be transmitted in a 
digitally encoded format. Still for purposes of facilitating the present 
description it will be assumed that the environment is that of a 
multichannel, repeatered, terminal-to-terminal communication network, a 
general illustration of which is shown in FIG. 1. 
Referring now to FIG. 1, there is shown a general block diagram of a 
repeatered, multichannel communication network to which the present 
invention may be applied, where information is to be conveyed between 
geographically separated locations identified as a West location and an 
East location. For purposes of facilitating the description and 
illustration of the invention, the network will be reduced to a simplified 
communication configuration contained only two spaced apart locations 
between which information is to be conveyed. It should be understood 
however, that more than two separate locations may be interconnected with 
each other over respective network sections established between each pair 
of locations. FIG. 1 illustrates the configuration of an individual 
section of the network wherein a pair of terminal stations 10 and 12 
geographically remote from each other at respective West and East 
locations are coupled together over a plurality of normally active 
transmission channels 13 and a protection channel 14 to be described 
further below. Where the overall network is comprised of more than only 
the two separate locations shown in FIG. 1, separate sections are 
associated with each pair of locations between which communications are to 
be conveyed, with the sections being linked together in a back to back 
chain configuration to complete the overall network. Since the network 
configuration will be assumed to be reduced to only a single section 
coupling a pair of geographically separated locations to each other, the 
terms network and section may be considered to be synonymous, except in a 
few isolated instances where reference to separate sections of a larger 
(than two) network will be made. For purposes of the present description 
it will be assumed that the information to be conveyed over the network is 
in the form of digitized telephone traffic, although it should be 
understood that the particular type of information transmitted via the 
system is not critical. The digitized telephone signals may represent 
voice, data, etc., namely, whatever signals may be digitized into a 
suitable format for high speed, high density data communication. 
Situated at one end of the network at a West location and coupled to a 
telephone signalling interface (not shown) is a first terminal station 10. 
Terminal station 10 provides full duplex transmission capability between a 
telephone interface such as an interoffice trunk, or digital microwave 
interface and a multichannel communication highway such as the fiber optic 
highway described in the above-referenced application, comprised of an 
N-channel link 13 and a protection channel link 14. Each channel is 
configured of a pair of communication links, one for transmitting signals 
in one direction (e.g. West to East) and the other for transmitting 
signals in the reverse direction (e.g. East to West). In the present 
description it will be assumed that six channels make up the system, 
including five normally active or used channels and one normally quiescent 
or protection channel. It should be understood, however, that the number 
of channels that may be employed is not limited to the particular number 
chosen in the example described, but may be any suitable number as the 
need demands. The protection channel 14 is normally not used but is 
provided in the event of a failure of one of the five active channels of 
link 13. 
From terminal station 10 at the West end of the network, fiber optic links 
13 and 14 are coupled to a repeater 11 which is further coupled to 
additional links 13 and 14 to terminal station 12 at the opposite end or 
East end of the network. Repeater 11 provides the necessary signal 
regeneration to ensure proper signal transmission, via the channel links, 
reception and data recovery at the receiving terminal station 12. While 
only a single repeater 11 has been shown in FIG. 1 so as to simplify the 
drawing, it should be understood that more repeaters may be serially 
situated along the link between terminal stations 10 and 12 as the 
distance between terminal stations at opposite ends of the network 
increases. 
Like terminal station 10, terminal station 12 provides full duplex 
transmission capability between an associated local telephone interface 
(not shown) and the multichannel communication highway. Each terminal 
station contains suitable data encoding/decoding transceiver equipment for 
coupling incoming digital telephone traffic onto respective ones of the 
channels 13 and 14 for transmission to the other station. This transceiver 
equipment provides for multiplexing the serialized digital telephone 
traffic with auxiliary or overhead data that is used for synchronization 
and control purposes. Although, as far as the present invention is 
concerned, the particular data format or multiplexing transceiver 
equipment that is used is not critical and will not be described in detail 
here, it may, advantageously, comprise components such as those described 
in the above referenced application and attention may be directed to that 
application for a detailed explanation of the same. Suffice it to say, for 
the purposes of the present description, that the multiplexing equipment 
of each terminal station is equipped to couple prescribed auxiliary or 
overhead bits in common to the transceiver equipment for each channel. 
With this general communication network configuration providing the basic 
transmission facility to which the present invention may be adapted, 
terminal station 10 is further associated with a voice/alarm interface 
module 17 while terminal station 12 is coupled to its own respective 
voice/alarm interface module 18. It is through these modules that 
supervisory personnel in stations 10 and 12 communicate with each other 
using the repeatered channels of the network. The interface module 
receives input voice or alarm signals from an attendant at one terminal 
station, encodes these signals and applies them in common to each 
transceiver associated with channels 13 and 14 for redundant, parallel 
transmission to the other terminal stations. At the receiving terminal 
station the encoded voice/alarm data on one of the channels is selected 
and decoded by that station's voice/alarm interface module to reconstruct 
the original signal input by the attendant at the other terminal station. 
The configuration and operation of an individual interface module will be 
explained in detail below with reference to FIGS. 2A-2C. 
Referring now to FIGS. 2A-2C, there is shown in schematic block diagram 
form a voice/alarm, encode/decode interface module for implementing voice 
and alarm signal communications between terminal stations via the 
multichannel links of the network shown in FIG. 1. At one terminal station 
encoded alarm or voice signals are inserted into the data stream as 
overhead bits, transmitted over each of the available data links, and 
subsequently decoded at the addressed terminal station to recreate the 
transmitted alarm or voice. Telephone addressing schemes, such as rotary 
dial, frequency pulse keying, etc. are employed for identifying the 
terminal station being called. While only two terminal stations (10 and 
12) have been referenced in conjunction with the description of the 
system, it is again to be understood that a communication system embraced 
by the present invention may include more than two terminals, each of 
which forms one end of a point-to-point multichannel link. With this 
capability, each terminal station will have a telephone number address 
that may be dialed from an attendant's handset at another terminal station 
and the description of the interface module to follow will explain the 
equipment associated with a respective terminal station for implementing 
the voice/alarm encoding and decoding functions necessary to convert the 
telephone address, alarm and voice signals into the proper format for a 
response and completed communication. 
In order to facilitate an explanation of the voice/alarm interface module, 
the module may be considered to be subdivided into these section: 1--an 
encoding section which receives incoming dial pulse, voice or alarm audio 
signals, digitizes and encodes the signals and forwards the encoded 
digital signals onto the transceiver/multiplexer circuitry of the terminal 
station for transmission over each channel; 2--a decoding section which 
receives encoded digital signals transmitted from another terminal 
station, decodes the signals and outputs analog audio signals to the 
attendant's audio equipment. In the case of station address signals that 
identify the terminal station being called, the decoding section carries 
out address signal detection functions and energizes an alarm to the 
terminal station operator. Finally, there is an alarm monitoring section 
that responds to a longer than momentary signal lead input to energize an 
alarm. Each of these sections will be described separately below. For 
purposes of simplifying an understanding of the invention, the various 
sections of the voice/alarm interface module under consideration will be 
assumed to be those associated with the module 17 associated with terminal 
station 10. 
ENCODING SECTION 
When the attendant at terminal station 10 wishes to place a call to another 
terminal station (e.g. terminal station 12), the attendant addresses that 
station by way of a conventional handset signalling device, such as rotary 
dial, frequency pulse keys, momentary switch, etc. provided at the 
station. The type of signalling device used is not critical and merely 
provides means for addressing the voice/alarm interface module at another 
terminal station. 
Input address signalling lines 101 for dial pulse signals, lines 102 for 
rotary pulse signals and lines 103 for momentary switch pulses (CALL) are 
coupled to a conventional pulse-to-tone converter 104 which produces a 
dual audio tone output at a selected pair of frequencies of 2.9 KHz and 
3.3 KHz on line 105 in the presence of a closed contact pulse on any one 
of lines 101-103. The set of frequencies of 2.9 KHz and 3.3 KHz was chosen 
to ensure that the equipment will be capable of distinguishing between 
voice and tone signals. In some instances a voice frequency signal may 
have such a frequency content that it might be recognized as a tone 
signal. However, with the use of a pair of non-harmonically related 
frequencies spaced apart by the 400 Hz differential, which will not be 
duplicated by a voice signal, a clear line of demarcation between true 
voice signals and a true tone pair can be effected. The tone pair signals 
themselves are produced by a pair of tone generator/detector circuits 60A 
and 60B, the tone outputs f.sub.A =3.3 KHz and f.sub.B =2.9 KHz of which 
are coupled over lines 106A and 106B to be summed together in summing 
amplifier 180 and applied over line 265 to the tone input of pulse-to-tone 
converter 104. The pulse signals that are applied to converter 104 over 
one of input lines 101, 102 and 103 effectively gate the dual tone 
summation signal on line 265 and apply the resulting tone burst signal to 
output line 105. The gating pulses, per se, are coupled over output line 
239 to one input of gate 238. 
Line 105 is coupled to one input of each of summing amplifiers 111 and 121. 
The output of summing amplifier 111 is coupled over line 266 to a low pass 
filter 267. Summing amplifier 111 is also coupled to receive incoming 
voice signals from auxiliary voice interface circuitry at terminal station 
10. For this purpose a strapped voice input twisted pair 112 is 
transformer coupled via isolation transformer 113 and line 114 to one 
input of summing amplifier 111. Line 114 is also coupled to one input of 
another summing amplifier 117, the output of which is coupled over line 
116 to deliver applied audio signals (voice or tones) to the earphone or 
speaker of the attendant's audio set, e.g., handset or headset. The output 
of amplifier 121 is coupled over line 120 to an isolation transformer 119. 
The output of isolation transformer 119 is coupled via twisted pair 118 to 
strapped audio output equipment. Thus, through summing amplifier 117 and 
121, the tone signals produced by converter 104 are applied to local audio 
equipment. 
The tone or voice signals produced at the output of low pass filter 267 are 
coupled over line 135 to a companding A - D converter 136 which is clocked 
by a suitable clock generator 156 (1.536 MHz) via line 155. The output of 
clock generator 156 is further coupled to a timing signal generator 271 
and to the ENCODE/DECODE CLOCK input of a multiplex terminal unit (MTU) 
140. Timing signal generator 271 is comprised of suitably configured 
combinational logic to produce timing signals that control the operation 
of A - D converter 136, register 138 and MTU 140. The basic clock is 
derived from the 1.536 MHz clock on line 155 and generator 271 responds to 
outputs of MTU 140 on links 275 and 276 to produce sequential operational 
timing signals, described below. The sampled and quantized audio signal is 
digitized into a suitable code resolution, e.g., eight bits, to produce an 
eight-bit serial output code for each sample, which code is coupled over 
link 137 to serial shift register 138. The serial NRZ output of shift 
register 138 is supplied over line 139 to the NRZ IN terminal of (MTU) 
140. (MTU 140 may comprise a commercially available NRZ-MANCHESTER-NRZ 
encoding/decoding unit such as an HD1-15531 unit manufactured by Harris 
Corporation). MTU 140 encodes the serial NRZ data on line 139 into a 
sixteen-bit Manchester word (3 sync bits, 8 data bits, 4 spare bits and 1 
parity bit) at a suitable bit rate (128 Kbs) and outputs the encoded 
bipolar data over line 141 to buffer amplifier unit 142. Buffer amplifier 
unit 142 includes six amplifiers (for the five channels of link 13 and the 
one protection channel of link 14 shown in FIG. 1.) through which encoded 
data signals are converted to ECL logic levels and applied over link 143 
to each of the five normally used and the one additional uplink 
transmission channel for application to the transceiver in terminal 
station 10 associated with each channel. As was pointed out above, the 
timing of the fetching of the digitized data by MTU 140 is controlled via 
timing signal generator 271 which responds to the 1.536 MHz clock on line 
156 and the outputs of MTU 140 on links 275 and 276 to produce shift clock 
pulses on line 276 to read out the contents of register 138 and line 272 
which delivers control timing signals to A-D converter 136 as MTU is ready 
to receive and encode more data samples. As a new audio data sample is to 
be encoded, timing signal generator 271 delivers an encode enable control 
signal over line 274 to the encode enable input of the MTU 140. 
In operation, when the attendant at terminal station 10 places a call to 
terminal station 12, the address of the terminal station is applied via a 
dialing device to pulse-to-tone converter 104. Pulse-to-tone converter 104 
pulses out an audio signal corresponding to the summed tone pair signals 
on line 265 from tone detector/generators 60A and 60B, in accordance with 
these pulses, on output lines 105 and 239. The tone pair on line 105 is 
coupled through summing amplifier 111 and low pass filter 267 to A - D 
converter 136, wherein the pulsed tone pair signals are digitized. These 
digital signals representative of the address of the called station are 
then encoded by MTU 140 and applied over each line of output link 143 to 
be applied in parallel to the transceiver units associated with each 
outgoing channel. Through the multiplexing circuitry of the transceiver 
units, the encoded tone pair address bits are inserted into the outgoing 
data streams of each channel and transmitted over each data link to the 
remote terminal station. In a similar manner, voice signals, either from 
the attendant's handset equipment or from auxiliary audio equipment, are 
coupled directly to the other inputs of summing amplifier 111 and 
subsequently digitized and enabled for transmission over each channel. 
DECODING SECTION 
The description of the decoding section of the module to follow will 
proceed from the standpoint of a received call from another terminal, 
i.e., the data contained in the received overhead bits that have been 
demultiplexed by the transceiver/demultiplexing equipment of the terminal 
station. It will also be assumed that the address tone pair designates the 
address of the terminal station 10. 
Via a suitable thumbwheel switch located externally to the module, the 
attendant can select one of the six incoming channels to be monitored for 
address, voice/alarm data. The digital code produced by the setting of the 
thumbwheel switch will be applied over lines 147 which designate over 
which line the communication return from the other station is to be 
received. Accordingly, one of the lines of link 146, after appropriate 
logic level translation, is coupled via multiplexer 144 over line 145 to 
the Manchester data input of MTU 140. The incoming Manchester words that 
are comprised of successively received address or voice/alarm bits are 
decoded by MTU 140 into a twelve-bit NRZ data word (8 data bits, 4 spare 
bits) and supplied over line 148 to serial-in, parallel-out shift register 
134. Clocking of the decoded NRZ words from MTU 140 into register 134 is 
controlled by TAKE DATA and SHIFT CLOCK OUT signals applied by MTU 140 
over lines 151 and 149, respectively, to AND gate 150, the output of which 
is coupled via line 152 to the clock or shift control input of register 
134. Line 151 is further coupled to a load inhibit input of a storage 
register 132 and to a counter 158. When MTU 140 detects valid data it 
supplies a VALID DATA signal on line 130 to the clock input of storage 
register 132, so that the decoded data byte clocked into serial-in, 
parallel-out register 134 may be loaded via link 133 in parallel into the 
eight stages of register 132. 
The contents of storage register 132 are coupled over link 131 to 
companding D - A converter 127 which supplies an analog output over line 
126 to lowpass filter 125. Filter 125 removes quantization noise from the 
audio signal and applies the resulting signal over line 124 to summing 
amplifier 121, tone detectors 60A and 60B and to a controlled attenuator 
261. One input of AND gate 263 is coupled via line 268 to the output of OR 
gate 251, while a second input of AND gate 263 is coupled via line 167 to 
the Q outut of a retriggerable one-shot 165. The Q output of one-shot 165 
is normally low except during receipt of incoming address dial pulses, as 
will be explained below. The output of AND gate 263 is coupled over line 
262 to the control input of controlled attenuator 261, which contains a 
controlled active resistor, such as an FET, that reduces the amplitude of 
a tone signal output of filter 125 to a level acceptable for human hearing 
and applies the attenuated tone signal over line 264 to one input of 
summing amplifier 117 so that the incoming tone signals may be delivered 
to the attendant's voice output circuit. 
In addition to the initial decoding of received tone and voice input 
signals, the voice/alarm interface module contains dial pulse/call and 
alarm signal monitoring circuitry which is capable of decoding the digits 
dialed or an alarm signal generated by either the local calling party or 
received over the multichannel link from a remote calling party. For 
incoming dialed address signals from a remote terminal station, such as 
terminal station 12 to terminal station 10, the module compares the dialed 
digits to its own station code and signals the attendant if it determines 
that the call is for terminal station 10. Circuitry is also included for 
generating a misdialing error signal if the dialed digits are not properly 
dialed by either the local calling party on an outgoing call, or by the 
remote calling party on an incoming call. If an alarm tone is generated by 
either party, this signal is also detected and causes a local alarm signal 
to be generated at each terminal station. 
As was explained above, an incoming call will contain dialed digit tone 
pair pulses to be eventually followed by voice signals from the remote 
terminal. In the configuration shown in FIGS. 2A and 2B, the dial signal 
monitoring circuitry is capable of handling up to one thousand addresses, 
using a three digit dialed decimal number addressing scheme. It should be 
understood, of course, that the size of the address code is not critical 
and may be tailored to suit the requirements of the user without departing 
from the basic implementation of the present invention. 
Now, using the three decimal digit addressing scheme referred to above, 
when a call is placed, the dialed decimal digits are encoded in a dual 
tone formal and delivered over the multichannel link to another terminal 
station. In the present example it will be assumed that terminal station 
10 has the three digit decimal address 010, so that using rotary dial 
equipment, for example, at the remote calling station, the calling party 
will have dialed the sequence: ten pulses - one pulse - ten pulses. Thus, 
at terminal station 10 there will be received a sequence of ten tone 
pulses - one tone pulse - ten tone pulses. As the first received group of 
ten tone pulses are decoded and reproduced in analog form at the output of 
D - A converter 127 they are filtered by low pass filter 125 and applied 
to tone detectors 60A and 60B. The outputs of tone detectors 60A and 60B 
are coupled over respective lines 161A and 161B to OR gate 251. The output 
of OR gate 251 is coupled via line 268, OR gate 238 and line 252 to the D 
input of a flip-flop 162. Flip-flop 162 is clocked via line 159 from the 
output of a divide-by-ten counter 158 which is coupled via line 151 to the 
TAKE DATA output of MTU 140. The TAKE DATA output from MTU 140 provides a 
clock signal at 8 KHZ to control the sampling rate of converter 127, via 
register 132, and counter 158 divides this clock signal down to a value 
suitably less than half the sampling rate for proper tone signal 
monitoring. Thus, during the presence of tone pulses detected by either of 
tone detectors 60A and 60B, counter 158 will clock flip-flop 162 via line 
159, causing its Q output line 163 to go low and its Q output line 164 to 
go high. 
Line 163 is coupled to one input of an AND gate 168, a second input of 
which is coupled over line 166 to the Q output of retriggerable one-shot 
165. Line 165 from the Q output of flip-flop 162 is coupled to the input 
of one-shot 165 and to the reset input of a flip-flop 194. The Q output of 
one-shot 165 is coupled via line 167 to the clock inputs of flip-flops 194 
and 198. The D input of flip-flop 194 is strapped to +V, so that if line 
164 is high, flip-flop 194 is set in response to an output signal from the 
Q output of one-shot 165 on line 167. The Q output of one-shot 165 is 
further coupled to the clear input of a dialed counter 170, to the clock 
input of flip-flop 231 and to the trigger input of a further one-shot 210. 
The output of AND gate 168 is coupled to the clock input of dialed digits 
counter 170. Counter 170 counts the number of pulses produced for each 
dialed digit and couples its contents over link 171 to a comparator 172. 
Comparator 172 is also coupled via links 173, 174 and 175 to gate circuits 
176, 177 and 178. Gate circuits 176-178 are coupled to BCD digit code 
links 179-181, respectively, the latter being hard-wired to prescribed 
logic levels that identify the digit address of terminal station 10. Thus, 
for the example chosen, link 179 will couple the 4-bit code "1010" to gate 
circuit 176, link 180 will couple the code "0001" to gate circuit 177 and 
link 181 will couple the code "1010" to gate circuit 178. Gate circuits 
176-178 are sequentially enabled by AND gates 187, 186 and 185 
respectively, as incoming dialed digit pulses are analyzed. For this 
purpose flip-flops 198 and 201 are coupled in cascade to form a stepping 
circuit that is incremented for each newly-received digit as a new delayed 
pulse is produced by one-shot 165. This action causes flip-flop 198 and 
201 to selectively enable one of AND gates 187-185 as each new dialed 
digit tone pulse sequence is detected by tone detectors 106A and 106B. As 
was pointed out above, one-shot 165 is retriggerable and produces a pair 
of complementary delay pulses of a suitable width in response to a trigger 
signal at its input. This delay pulse width is wide enough to encompass 
the maximum time span of a dialed digit pulse. When a sequence of pulses 
that make up a digit is clocked through flip-flop 162 over line 164, 
one-shot 165 is repeatedly retriggered, thereby extending the width of the 
delay pulses on lines 166 and 167 until it times out after the last pulse 
of the digit. Therefore, AND gate 168 remains enabled for the entirety of 
the duration of the dialed digit. 
As AND gates 187-185 are selectively enabled, the strapped BCD code input 
to one of gate circuits 176-178 is applied over a respective one of links 
173-175 to comparator 172 to be compared with the dialed digit count 
accumulated in digit counter 170. If a match occurs, a signal is applied 
over line 232 to the D input of flip-flop 193. 
Flip-flop 193 is clocked via line 159 by the output of divider 158. The Q 
output of flip-flop 193 is coupled over line 192 to one input of AND gate 
191, the second input of which is coupled to the Q output of one-shot 165 
via line 167 as described previously. Flip-flop 193 and AND gate 191 
function to supply a dialed digit recognition signal for a respective 
dialed digit over line 190 to a shift register 189 when comparator 172 has 
detected a digit match, but the output of comparator 172 is prevented from 
being loaded into shift register 180 until the Q output of one-shot 165 
changes state indicating that the length of time sufficient to cover the 
span of the last pulse of the dialed digit has elapsed. 
Shift register 189 accumulates a count corresponding to the number of 
decimal digits employed for a station address (three in the present 
embodiment) and supplies an output signal over line 233 to OR gate 196 
upon the completion of a successful three decimal digit address comparison 
by address comparator 172. The output of OR gate 196 is coupled over line 
197 to the clock input of flip-flop 211, while the D input of flip-flop 
211 is coupled over line 295 and resistor 234 to high potential (+V). The 
Q output of flip-flop 211 is coupled over line 212 to a relay driver 214, 
the output of which is coupled over line 215 to the base of a switching 
transistor 219 within a relay circuit 216. The collector of transistor 219 
is coupled through the parallel connection of diode 217 and relay winding 
218 to positive potential while the emitter of transistor 219 is grounded. 
Relay contacts 220 of relay circuit 216 are coupled to a signalling alarm 
(e.g. bell) through lines 221. The reset input of flip-flop 211 is coupled 
over line 222 to a normally open ACKNOWLEDGE SWITCH 223 that is depressed 
by the attendant in answer to the ringing alarm signal. A ringing alarm 
signal is generated when flip-flop 211 is set by a signal on line 197 from 
OR gate 196, which causes the Q output of flip-flop 211 to go high. This 
signal is coupled through buffer 214 to turn transistor 219 on and switch 
the contacts 220 of relay 216. 
The Q output of flip-flop 211 is coupled to one input of AND gate 208 and 
to AND gate 204 via line 206, and is used to reset various components of 
the dialed digit monitoring circuitry in response to an ACKNOWLEDGEMENT 
signal, as will be described more fully below. The output of AND gate 208 
is coupled over line 207 to reset flip-flop 231. The output of AND gate 
204, which is also coupled to line 206, is coupled via line 188 to clear 
flip-flops 198 and 201 and shift register 189. AND gate 204 also has an 
input coupled via line 205 to the Q output of one-shot 210. The Q output 
of one-shot 210 is coupled via line 209 to the clock input of flip-flop 
235. The D input of flip-flop 235 is coupled to the Q output of flip-flop 
231, the clock input of which is coupled to the Q output of one-shot 165, 
as explained previously. The D input of flip-flop 231 is coupled over line 
184 to the output of AND gate 185. When AND gate 185 is enabled, so that 
the BCD code for the third digit is coupled via gate circuit 178 to 
comparator 172, the D input of flip-flop 231 goes high so that at the 
change in state of the Q output of one-shot 165, the Q output of flip-flop 
231 goes high, indicating a completion of the loading and comparison of 
the third digit or complete number of the station address by digit counter 
170 and comparator 172. After a time out interval governed by one-shot 
210, flip-flop 235 is clocked via the Q output of one-shot 210 over line 
209. If flip-flop 231 has been set by a recognition of three complete 
digits for terminal station 10, the Q output of flip-flop 231 will have 
been high causing the Q output of flip-flop 235 to go high in response to 
the clock pulse on line 209. The Q output of flip-flop 235 is coupled over 
line 237 to a timing signal generator 128. Generator 128 produces a low 
frequency (2 Hz) interruption signal for a brief period of time (5-10 
sec.) and applies this signal over line 129 to one input of AND gate 123 
and over line 129 and via inverter 130 to clear flip-flop 235. During the 
time out interval that timing signal generator 128 generates the 2 Hz 
signal, AND gate 123 interrupts the 800 Hz produced by divider 158 over 
line 159 to supply an audible tone over line 122 to summing amplifier 117. 
The purpose of the interrupted 800 Hz audio signal produced by AND gate 
123 is to provide a misdialing error alarm signal to the local attendant. 
As was pointed out above, for the purpose of describing a working example, 
the dialed digit address of terminal station 10 is assumed to be the BCD 
address "010". This address will be strapped in BCD format with the 
appropriate logic levels applied over links 179 through 181 to gate 
circuits 176 through 178. When the initial dialed digits of an incoming 
call for terminal station 10 are reconstructed by companding D - A 
converter 127, they are coupled through low-pass filter 125 and the 
successive tones are decoded into digital pulses by tone detectors 60A and 
60B. These pulses are coupled through gates 251 and 238 and applied to the 
D input of flip-flop 162, which is clocked by the output of divider 158. 
Flip-flop 162 effectively removes undesired transients in the output of 
tone detectors 60A and 60B and applies the pulses as they are received to 
AND gate 168. As the pulses are clocked through flip-flop 162, the initial 
change in state of the Q output of flip-flop 162 on line 164 triggers 
retriggerable one-shot 165. For the first pulse, the Q output of one-shot 
165 goes high for a prescribed period of time, (for example 200 
milliseconds to cover the greatest width of any pulse within a digit that 
may be encountered) while the Q output of one-shot 165 goes low for the 
same period of time. Incoming pulses are thereby gated through gate 168 
and counted by digit counter 170. In addition, during receipt of the tone 
pair pulses, AND gate 263 is enabled thereby inserting a resistor in the 
path between output line 124 from filter 125 and input line 264 to summing 
amplifier 117 so as to make the audio level of the tone pulses acceptable 
to the attendant. 
The state of flip-flops 198 and 201 at this time are such as to initially 
enable AND gate 187 and thereby gate circuit 176 so that comparator 172 
will compare the contents of the digit counter 170 with the strapped digit 
code on input link 179. When one-shot 165 has timed out through the last 
pulse of the first digit received, its Q and Q outputs change state, 
thereby enabling AND gate 191. If the contents of the first digit and the 
first strapped digit of the terminal station match, comparator 172 will 
have caused flip-flop 193 to be set, thereby enabling both inputs of AND 
gate 191 and causing an initial pulse to be loaded into shift register 
189, as one-shot 165 changes state. 
As the next two digits are received, the above oeprations are repeated and 
the contents of shift register 189 are advanced until three successive 
digits have been recognized and therefore three pulses have been loaded 
into shift register 189. At this time, the contents of the third stage 
will cause the output on line 233 to go high, thereby applying a signal to 
the clock input of flip-flop 211 over line 197. This sets flip-flop 211 
and thereby energizes relay circuit 216 to cause the alarm contacts that 
are coupled to lines 221 to be closed, and energize whatever circuit is 
coupled to the alarm contacts, such as a bell circuit. To answer a call, 
the attendant momentarily depresses the acknowledge switch 223, thereby 
resetting flip-flop 211 and terminating the alarm. The resetting of 
flip-flop 211 further enables AND gate 208 and AND gate 204. Time out 
one-shot 210 which was triggered by the output of one-shot 165 eventually 
has its ouptuts change state, thereby causing flip-flops 198, 201 and 231 
to be reset and shift register 189 to be cleared, so that, again, for 
subsequent calls the dialed digits that identify the address of terminal 
station 10 may be recognized and decoded, with the alarm eventually 
energized. 
Subsequent voice signals from the calling station are coupled through 
low-pass filter 125, as well as summing amplifiers 117 and 121 to the 
local orderwire output circuits to the attendant. During receipt of voice 
signals, the attenuating action of controlled attenuator 261 is not 
activated as AND gate 263 is disabled. 
If the digits decoded by comparator 172 have failed to match the strapped 
digit code for the terminal station, namely, the call was addressed to 
another terminal station, the output of comparator 172 would not have 
caused flip-flop 193 to be set, so that shift register 189 would not have 
been loaded with three consecutive pulses identifying a satisfactory 
comparison for all three digits. As a result, flip-flop 211 would not have 
been set and no alarm would have been generated by relay circuit 216. 
Eventually, one-shot 210 would have produced an output over line 205 to 
reset the components of the decoding circuitry, just as the end of a 
normal digit detection. 
If the calling party does not dial a complete number then, as flip-flops 
198 and 201 are incremented to count each dialed digit, the output of AND 
gate 185 will be of such a level as to change the state of flip-flop 231. 
As a result, the input to flip-flop 235 will be of a state such that when 
one-shot 210 times out, the output of flip-flop 235 supplies a signal over 
line 237 to timing signal generator 128. Timing signal generator 128 
produces an interrupting two Hz signal over line 129 for a period of 5-10 
seconds so that AND gate 123, which also receives the 800 Hz output of 
divider 158, supplies an interrupted 800 Hz tone over line 122 summing 
amplifier 117 advising the local attendant of an incorrectly dialed 
number. At the end of the interrupting period, the state of line 129 is 
such that inverter 130 clears flip-flop 135 and removes the dialing error 
signal tone. 
ALARM MONITORING SECTION 
In addition to signalling the attendant for the receipt of a sequence of 
dialed digits, the interface circuitry is also capable of detecting an 
alarm signal, namely a continuous tone in excess of a prescribed period of 
time, (for example, considerably greater than the time out period of 
one-shot 165 or 200 milliseconds). Typically, the depression of the 
momentary switch on the attendant's console through which a call tone is 
provided will be on the order of one-third to one-half a second. This tone 
will cause a steady output to be provided on line 164 from flip-flop 162, 
so that flip-flop 194 will be set and supply a signal line 195 through OR 
gate 196 to set flip-flop 211 and thereby energize the alarm via relay 
circuit 216. The attendant then answers the alarm by depressing the 
ACKNOWLEDGE switch 223 to reset flip-flop 211 and thereby disable relay 
circuit 216, as discussed above. 
The above described digit decoding and alarm monitoring sections also 
operate to monitor the proper dialing of an outgoing call. The pulses that 
are applied over one of the lines 101-103 to pulse-to-tone converter 104 
are applied over line 239 through gate 238 to the D input of flip 162. The 
remainder of the circuitry operates in the same manner described above for 
incoming pulse signals applied over line 268 to gate 238 in response to 
incoming tone pulse signals. 
As will be appreciated from the foregoing description of the present 
invention, voice and alarm signalling capability between supervisory 
personnel at monitor and control sites located at the separated 
transceiver facilities of a (repeatered) multichannel communication 
network is provided exclusive of normal telephone equipment by a 
multichannel multiplexed encode/decode scheme in which voice and/or alarm 
signals generated at one station are digitally encoded and formatted so as 
to be inserted, directly at the end of the network, into the data stream 
of the normally conveyed data traffice over the active channels of the 
network. Because the encoded signals are inserted as overhead bits for 
each active channel, a fault on interfaced telephone equipment or on one 
of the channels will not prevent the completion of transmission of the 
intended communcation between terminal site personnel. Moreover, by having 
redundant access to all of the channels over which the telephone traffic 
conveyed by the network is serviced, station operation personnel have the 
capability of monitoring the "ear-input" quality of the voice signals 
heard by the subscribers of the network. 
While we have shown and described one embodiment in accordance with the 
present invention, it is understood that the same is not limited thereto 
but is susceptible of numerous changes and modifications as known to a 
person skilled in the art, and we therefore do not wish to be limited to 
the details shown and described herein but intend to cover all such 
changes and modifications as are obvious to one of ordinary skill in the 
art.