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CROSS REFERENCE TO RELATED APPLICATION
Of interest is U.S. application Ser. No. 793,428, "Telecommunication
Management and Control System", filed by the present inventors on May 3,
1977.
BACKGROUND OF THE INVENTION
The invention relates to a communications line control system and more
specifically relates to a control system for controlling and recording the
use of long-distance communication circuits.
Until recently, PBX or CENTREX users were limited to dial access and manual
access through an operator to long-distance or bulk facilities. In a dial
access system, the users completed the call or, if all of the bulk
facilities were busy, obtained blocking, i.e., trunk busy signals. In a
manual system, an operator placed the call, generally after toll ticketing
it manually, over bulk facilities or long distance and, if requested,
manually queued the call by calling back the user when the appropriate
bulk facility was available. More recently, the telephone company has
introduced various modes of flexible route selection systems (FRS) whereby
a user's call may be automatically processed on a number of different
types of bulk facilities, depending on the route selected by the user. In
order to enhance the use of the bulk facilities, the concept of automatic
queueing of calls by holding onto their line for a specific time,
generally 30 to 60 seconds, was implemented. Such automatic queueing
allowed more efficient use of the bulk facilities and thereby lowered the
cost per minute to the user. However, in each of these cases, cost is
generally traded off with service, as will be explained.
A manual system is inefficient with respect to obtaining access for a user
to a particular desired bulk facility because the operator controls the
call and it is somewhat inefficient with respect to utilization of the
bulk facility per se. In a manual system, the operator must note that the
desired facility has become available, generally by observing a light, and
then call back the user before placing or dialing the call on the bulk
facility. During this interim period, the facility is not used, thus
rendering the system inefficient.
Dial access systems, wherein the user dials the facility directly on a
hit-or-miss basis, are inefficient. The user often obtains a busy signal
and, since no indication is provided as to when the facility will become
available, the line often sits idle while the user waits.
Dial access systems can be provided with an alternative method of accessing
bulk facilities, commonly termed "hold-on" queueing, whereby the user
waits for a bulk facility to become available with his telephone off-hook.
In such systems, the user is either passed immediately onto a line or
waits, generally for up to 60 seconds, for a line to become available. If
no line in the desired bulk facility becomes available during that period,
the call is overflowed to other more costly facilities or direct distance
dial trunks (DDD). While hold-on queueing increases the likelihood of the
user gaining access to the bulk facility, as compared to dial access
systems without hold-on queueing, the user is often overflowed before a
bulk facility is accessed. The average duration of a business telephone
call is on the order of five (5) minutes. Accordingly, the likelihood of a
bulk facility becoming available during the 60 second hold-on period is
relatively small. Larger hold-on periods are impractical in that the
user's line is tied up during the hold-on period.
The longer the user is willing to wait, the greater the likelihood that a
particular bulk facility, line or group of lines will be available for
placing the call. Thus, it is desirable to provide a call-back system
wherein the user can wait for a relatively long period of time for a
facility to become available, without tying up his line for that period or
requiring that the facility stand idle while the user or operator redials
the called number.
A call-back system in accordance with the present invention provides the
automatic calling back and placing of calls through electronic means and
is able to store the called number so that neither the user nor operator
has to redial the called number when the bulk facility becomes available
and, further, wherein the user's line is not tied up during the waiting
period. The caller enters the least-cost routing system by dialing an
access code through his PBX or CENTREX. After obtaining a system dial
tone, entering an account number (if required), the long distance number
(10 digits, speed or tie line) is dialed. The computer checks the
least-cost routing table to see if an appropriate line is available. If a
line is available, the call is automatically outdialed, but if one is not
available, the caller is given an All Trunks Busy signal and then return
of the system dial tone. The caller then enters the extension of the PBX
or CENTREX to be called back. The computer processor stores the call-back
number and the long-distance number and places the call in an appropriate
queue, in accordance with a predetermined priority classification of the
user or call.
The call continues to move up in the queue and when the appropriate line
becomes available, the computer controls the system to dial out the
extension of the caller through the PBX or CENTREX. When the caller goes
off-hook, the system then grabs the available line (which has been saved
during the call-back period) and automatically places the call on the bulk
facility for the caller.
If the caller is using his telephone at the time of call-back, the system
detects the busy indication and places the call-back in queue and will
continue to try until the call-back can be placed.
Obviously, during the waiting period, the caller can accomplish other work
and the system operates in the most efficient and economical manner by
"holding" the calls until the correct line is available.
It is most important to recognize that the smaller the group of bulk
facilities, the more important it is to have a long waiting time in order
to maximize access by a particular user to the bulk facility. As an
example, if there is a single line group (like an intrastate line or an FX
line) and the users of the calling company average 5 minutes per telephone
call, it becomes apparent that the likelihood of obtaining the single line
becomes greater, if it is in use, the longer the caller waits. If the
waiting period is 30 or 60 seconds for the 5 minute call, the chances of
getting the line are small, about 60/300 seconds or 20%, depending on when
the caller enters the system. If the caller has automatic call-back
capabiility, as in a system in accordance with the present invention, he
may wait up to the predesignated time, usually 10 minutes and the
likelihood of having the call placed on the bulk facility is excellent.
This system is, in fact, about 20% more efficient than an automatic
queueing system using hold-on and, because of the automation of placing
the calls and knowing when the line is available, about 12% more efficient
than operator queueing.
Copending application Ser. No. 793,428, "Telecommunications Management and
Control System", filed on May 3, 1977 by the present inventors, relates to
a method and apparatus, hereinafter referred to as the "least cost routing
system", for switching long-distance telecommunications circuits wherein a
central processing system is coupled to each of a plurality of remote
satellite switching units. Each remote satellite switching unit includes a
circuit routing matrix for connecting a local station to a selected
long-distance line which may, for example, be a local trunk line, bulk
rate lines such as WATS, foreign exchange or tie lines or lines between
remote units. The remote satellite switching unit also includes a
microcomputer system for detecting the status of outgoing lines from a PBX
or CENTREX and the destination of a requested call. This information is
transmitted to the central processing system which, in turn, selects the
least expensive line at any given time for transmitting the long-distance
call. The least expensive available line information is transmitted back
to the microcomputer system which provides command signals to the circuit
routing matrix to connect the requested call to the selected outgoing
long-distance line. The central processing system compiles a record of the
party placing the call, the long-distance line used, the time duration of
the call and line utilization of the system, and further observes the
status of the remote unit, etc. to compute a periodic account statement
for the subscriber.
The present invention is embodied in a similar system. It should be
appreciated, however, that, in the present invention, the circuit routing
matrix and outgoing line status detection may be incorporated into the
central processor (computer) rather than residing in remote satellite
switching units. The disclosure of such aforementioned copending
application Ser. No. 793,428 by the present inventors is herein
incorporated by reference.
A detailed description of a preferred embodiment of the present invention
is hereinafter given, with reference to the following drawings wherein:
FIG. 1 is a simplified diagram of the system configuration of the present
invention;
FIG. 2 is a schematic block diagram of the central processing system of the
present invention;
FIG. 3 is a block diagram of a switching unit of the present invention;
FIGS. 4 through 10 are more detailed schematic illustrations of the
components employed in a switching unit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
At the outset, a general overview of the operation and advantages of the
system of the present invention will be presented, followed by a detailed
description of the preferred embodiment thereof.
The present invention achieves cost reduction in long-distance
telecommunications calls through the highly efficient use of bulk-rate
communications facilities including WATS, foreigh exchange (FX) and tie
lines. Because a business organization pays a fixed monthly amount for
each such facility, the higher the traffic load or usage per facility, the
lower the cost of long-distance on a per minute basis. Thus, in operation,
the present system determines from the area code of the number being
called whether the subscriber or calling party has an FX or tie line
terminated in that area. If not, or if these lines are presently in use, a
determination is made as to the lowest cost WATS line available. If the
appropriate bulk facility is not available, the user is given an
indication of this and enters his extension into the system in order to be
called back. The user is placed in the appropriate queue for the
particular bulk facility and the system continues to process calls,
keeping the user in the queue for a preselected interval, e.g. ten minutes
if necessary, and calls back the user when the line becomes available.
Thus, the present invention achieves effective utilization of bulk
communications lines which may approach a 95% time utilization during peak
hours. The availability of local lines insures that no call will wait
longer than the predetermined selected interval.
To achieve this, a central processing system preferably communicates with a
substantial plurality of remote satellite switching units via leased
telephone lines or other commmunications links such as, for example,
satellite communications links. In the preferred embodiment, data is
transferred between the central processing system and the satellite
switching units in block mode using a suitable variable length message
format such as ASCII. The central processing unit controls all switching
functions and records the necessary data required for billing, generating
traffic statistics, etc. from the remote satellite switching unit. It
should be appreciated, however, that a call-back system in accordance with
the present invention can utilize a single central processor,
incorporating the functions of the remote satellite switching units. The
central processor and switching units can thus be an integral structure if
desired.
Three classes of trunk lines serve as an input to the switching units,
namely, rotary dial or tone dial branch trunks which pass from a
subscriber's CENTREX or PBX system, standard local lines and incoming WATS
service lines. The output trunks from the switching units also fall into
three classes, that is, bulk rate lines including outgoing WATS lines, tie
lines and/or foreign exchange (FX) lines, local trunk lines and lines to
recording devices. The present invention is capable of detecting either
tone or rotary dial from the input telephone circuits thereto and
addresses the output telecommunication circuit, by means of tone or rotary
dial signalling.
To place a long-distance call, a subscriber dials a special access number
via the PABX or CENTREX unit. The switching unit responds with a first
dial tone. The subscriber then enters a one-to-seven digit account number.
The switching unit acknowledges the number with a second dial tone if the
account number is valid or with an error signal if the number is invalid.
In the case of an invalid number, the first dial tone is reconnected after
providing an error tone, thus permitting a second try. After a second
invalid attempt, the subscriber is disconnected and the central processing
system flags that attempt. If valid, a second dial tone is heard by the
subscriber who then dials the desired long-distance number. In response
thereto, if no usable trunks are available, the system returns a busy
signal, e.g., three tone bursts and then returns a dial tone to the
subscriber. The subscriber may then hang up or may enter his call-back
number which is up to seven digits. This call-back number is generally the
telephone extension of the subscriber but may be an access code plus the
extension of the subscriber. Assuming that a number of subscribers have
encountered busy bulk rate lines and have requested the system to call
them back when a line becomes available, the system preferably has three
queues. Subscribers are called back in the descending order of queues
depending upon their respective positions within the queues. The number of
subscribers that can use the first or second queues is limited so that
those in the highest priority queues can have their calls connected to
long distance lines first. A user or call priority system can be
established by entering the call-back number into one of the respective
queues in accordance with predetermined account numbers or priority codes.
When an appropriate trunk is available for the subscriber who is waiting
for a call-back, the subscriber is called back. When the subscriber goes
off-hook, the tone signalling is transmitted into the network and at the
same time is fed back to the subscriber's telephone unit so that the
subscriber knows the call has been placed.
When the subscriber is called back, the unit will allow three rings to
occur before aborting the call-back. If the subscriber's extension is
busy, the system will recognize this and place the call-back in the
appropriate queue. If the subscriber desires to cancel the call, he may go
back on-hook at any time after hearing the transmission of the tone
signalling.
If desired, a special account number can be utilized on long-distance calls
in order that a particular account can be billed for the call. Thus, the
subscriber enters his subaccount number and upon receipt of the second
dial tone, the # key on the telephone tone keyboard and any number up to
ten digits followed by a second # key is keyed into the system. The system
records the number and returns the dial tone after which the subscriber
then dials the desired long-distance telephone number. An abbreviated dial
number can be keyed into the system in order to simplify the calling
procedure on the part of a subscriber. Thus, for example, if there is a
group of numbers which are used most frequently, these numbers can be
coded into a two-digit number and utilized in lieu of dialing or keying an
entire number. To use an abbreviated dial number, upon receipt of the
second dial tone, the subscriber enters an *, a two-digit number
corresponding to the number desired to be dialed followed by the entry of
a #. From rotary phones, two digits are entered, but the second digit
cannot be zero or one. The system then automatically retrieves the full
number from storage and places the call to the desired party. To enter an
abbreviated dial number into the system, the subscriber first enters his
account number. Upon hearing the second dial tone, he enters an *, any two
digits followed by an * and then a ten-digit telephone number. The system
signals its acceptance of the telephone number with a single tone burst or
signals its rejection with a two-tone burst. In connection with the
aforementioned, it should be understood that the specific format for
placing an abbreviated dial number call, etc., can be varied in keeping
with the invention by simply changing the logic, i.e., the algorithm, in
the central processing system and in the switching unit.
SYSTEM CONFIGURATION
Refer now to FIG. 1, where there is disclosed, in simplified block diagram
form, the preferred embodiment of the communications switching system of
the present invention. The switching system of the present invention
includes central processing system 11 of conventional design known in the
art and a plurality of remote satellite switching units 13. Again, an
integral central processor-switching unit can be utilized, if desired. As
contemplated, in the preferred embodiment, the central processing system
11 can provide control signals for controlling multiple satellite
switching units separately and in tandem. Each satellite switching unit 13
has a plurality of input lines connected thereto from voice connecting
arrangements 15. The voice connecting arrangement 15 provides isolation
between the output lines of a PABX or CENTREX unit 17 and the satellite
switching unit 13. Also connected to the input of the satellite switch 13
are local telephone lines 21 which are connected to the switch 13 via a
voice connecting arrangement 15. If desired, an INWATTS line can be
connected to the satellite switching unit 13.
At the output of the switching unit, a plurality of bulk rate and DDD
telephone circuits 26 are coupled to an output voice connecting
arrangement 27. As illustrated, the bulk rate lines typically include
OUTWATS lines, foreign exchange lines and tie lines. In order to assure
the availability of long-distance lines, the output of the switch 13 is
also connected to conventional business DDD lines which can be utilized to
convey long-distance communications, as desired.
The satellite switch 13 is operated in accordance with command signals from
the central processing unit 11. These signals are coupled to the satellite
switching 13 via a private data line 34 of conventional arrangement known
in the art. Should for any reason the private data line become unusable,
an alternative data line interconnect is obtained by automatic dial-up via
the DDD network in a conventional manner known in the art.
It should be understood that information signals containing, in coded form,
information with respect to the party called, the calling party, the
status of lines, etc., are conveyed via the data line switch 34 to the
Central Processing System 11 to provide the Central Processing System with
information by which a decision can be made as to which output lines
should be connected, disconnected, etc. It should also be understood that
while a private data line is used in the preferred embodiment of the
present invention, other data circuit methods for transmitting command
signals to the satellite switches and information from the switches to the
Central Processing System 11 can be utilized.
CENTRAL PROCESSING SYSTEM
Refer now to FIG. 2, where there is disclosed a more detailed schematic
block diagram of the Central Processing System 11. The Central Processing
System employs a minicomputer system which includes a digital computer for
performing the processing of the data from the remote satellite units. In
the preferred embodiment, the minicomputer system is an assembly of
standard components from Interdata, Inc., Model 7/32 Computer System;
however, it should be understood that a number of other systems in the
industry meet the application requirements of the invention. Interdata
standard components are used in the operation of the Central Processing.
The specific hardware and software thereof and, further, the application
program package used in the interoperation of the remote satellite unit
are identified in the appendix to the aforementioned application Ser. No.
793,428, by the present inventors.
The interoperation with the remote satellite unit is via data communication
circuits as aforementioned. The data communication circuits include
private line facilities and alternately can employ the switched network on
a dial-up basis. The interface with these facilities are commercially
available and, for example, are provided by the Bell Telephone System and
other independent companies. By convention, the interface between the
Minicomputer System and the telephone circuit includes data modem which,
in the preferred embodiment, employs a Bell 103 type unit or equivalent.
Further, the interface with the DDD network employ data access
arrangements (DAA) which, in the preferred embodiment, are commercially
available CBS data couplers.
Finally, as illustrated in FIG. 2, the central processing unit is redundant
with 100% duplication of the minicomputer system and related peripheral
components for the purpose of reliability. Interconnection between either
system and the data channels modem hardware is via the Fall Back Switch
arrangement, which in the preferred embodiment, employs a commercially
available Spectron Corporation Model FBS 1224.
REMOTE SATELLITE UNIT
Refer now to FIG. 3 where there is disclosed a more detailed schematic
block diagram of the remote satellite switching unit 13. Trunk lines from
one or more inlet exchanges are connected to a line control unit 41 of the
switching satellite unit 13 via the voice connecting arrangements 15.
Trunk lines to the outlet exchanges are connected from the circuit routing
matrix 51 via voice connecting arrangements 27.
The line control units 41 have the function of providing detection and
control of analog and DC signals on the trunk lines by means of a stored
program in the microcomputer system 49. The line control units 41
interconnect directly with the inlet voice connecting arrangements 15 and
with outlet voice connecting arrangements 27 via the circuit routing
matrix 51. The voice connecting arrangements typically employed for
interposition with Bell facilities are Bell VCA - CDQ2W for tie trunks
interconnect and CDH for any of the other aforementioned interconnects.
Each inlet voice connecting arrangement 15 is assigned to a line control
unit 41 and the associated inlet port on the circuit routing matrix 51.
Each outlet voice connecting arrangement 27 is assigned to an outlet port
on the circuit routing matrix. The voice connecting arrangements include
six interface leads per circuit which are conventionally identified as
CT/CR, CS/CG and CBS1/CBS2. The CTR and CR leads carry voice transmission,
tone address signalling and call progress signalling as is known in the
art. The CS/CG lines carry service request, answer/disconnect and DC dial
pulsing information. Finally, the CBS1/CBS2 lines carry line status
indication, seize/release and DC dial pulsing information. In the
preferred embodiment, two of these leads, that is, the CG and CBS2 leads,
are used as signal ground return for both of the voice connecting
arrangements 15 and 27 and the remote switching unit 13. These leads are
bonded to a common ground electrode. Accordingly, a four lead interface
per circuit is employed in the present invention and the circuit routing
matrix 51 is of the four pole type.
The output of each line control unit 41 is connected to the matrix switch
assembly 51 which, as will be more fully explained hereinbelow, includes a
matrix switching arrangement together with decoders and drivers therefor.
The circuit routing matrix 51 has the function of providing an
interconnect for the voice and signalling path between the line control
units 41 and the 2-of-8 tone transceiver 55 and the trunk lines to the
outlet exchanges. The circuit routing matrix is controlled by means of
control signals from the microcomputer system 49.
The 2-of-8 tone transceivers 55 have the function of providing detection of
touch-tone signals keyed into the system from a local subscriber telephone
unit. These signals are converted to binary digital signals which are
coupled to the central processing unit via the data line. In addition, the
push button tone transceivers 55 transmit 2-of-8 tone signals via the
circuit routing matrix 51 to outlet exchanges under the control of the
microcomputer system 49.
Private and Switch Network Data Arrangement 61 provides transmission of
signals on the data line linking the central processing system 11 with the
microcomputer system 49. The arrangement for passing low speed data
signals is of conventional design for the purpose of converting the
digital signals from the microcomputer 49 to appropriate analog signals
for transmission over the data link and for receiving analog signals over
the data link and converting these signals to digital signals for
processing by the microcomputer system 49. In the preferred embodiment, a
dedicated line 56 is provided so that access between the central
processing system 11 and the microcomputer 49 is on a continuous basis.
Should the private line for some reason be out of order, a backup line,
which preferably is a direct dial line, is also connected to the data
transceiver. The use of a DDD network for data communications is a
conventional technique employing Bell Data Access Arrangement CBS.
The operation of the line control unit 41, the switch matrix assembly 51
and the push button tone transceivers 55 is controlled by the
microcomputer system 49 which includes a central processing unit and
memory. Conventional control logic known in the art is employed in
interfacing the microcomputer system 49 with the line control unit 41, the
circuit routing matrix 51, the push button tone transceivers 55 and data
transceivers 61. Finally, a progress tone signal generator 58 is provided
for generating busy signals, error signals, etc. to advise the local
subscriber of the status of the telephone call being placed. The progress
tone signal generator accordingly is a conventional audio signal generator
which is connected to the line control unit through a matrix to be
explained more fully hereinbelow.
FIGS. 4-10 and the following description thereof is a more detailed
description and schematic presentation of the Remote Satellite Unit. The
unit is a hardware assembly of modules manufactured specifically for
performing the aforementioned control of communications circuits. The
hardware assembly is referred to in the preferred embodiment as an SST-1
Satellite Switch Terminal. As depicted in FIG. 3, it is composed of a
Microcomputer System 49, a Line Control Group 41, a Circuit Routing Matrix
51, a Tone Transceiver Group 55, a Tone Generator Group 58 and a Private
and Switch Network Data Line Arrangement 61. A detailed disclosure of each
of these equipments is given hereinbelow. Although one embodiment will be
described, it is to be understood that various changes and modifications
may be made by those skilled in the art without departing from the spirit
of the invention.
Refer now to FIG. 4, which is a detailed schematic illustration of the
Microcomputer System 49. The Microcomputer System 49 used to in the
preferred embodiment is a UP-607 Processor and SI-609 Scanner/Interrupt
and consists of commercially available components and elements that
interface with one another in an industry conventional configuration as
shown in FIG. 4. The Microcomputer System controls and communicates with
external components and equipment 41, 51, 55 and 61, in software
selectable modes by industry conventional methods through a system bus 90.
The basic central processing unit is a group of Large Scale Integration
(LSI) elements, which define the characteristics of the bus 90 and are a
part of the Intel Corp. MCS-80.TM. Microcomputer System. These elements
are a C8080A CPU 491, a D8224 Clock Generator and a Driver 492, C8228
System Controller 493 and a P8214 Priority Interrupt Control Unit 494. In
addition, the 8T95 and 8216 Interface Elements 492 and 494, respectively,
provide requisite bus buffer/driver capability.
An industry standard configuration of memory elements is employed in the
Microcomputer System and, as illustrated in FIG. 4, includes commercially
available C2708 UV Erasable Programmable Read-Only Memory (PROM) 495 and
P2102 Read Alternate Memory (RAM) 496. The stored program contained in the
PROM which is used in the remote satellite unit is appendixed in the
aforementioned copending application Ser. No. 793,428, by the present
inventors. The stored program is presented in its entirety in the assembly
language of the MCS-80.TM. Microcomputer System. Software select logic
used in addressing memory and other hardware elements throughout the
remote satellite unit employ conventional Small Scale Integration (SSI)
and Medium Scale Integration (MSI) logic elements. The specific decode
function is accomplished using 74LS138 MSI logic element.
The Microcomputer System provides a conventional serial data interface for
linking to the central computer system using a commercially available LSI
element Universal Asynchronous Receiver/Transmitter (USAR/T) 497, such as
Western Digital Corporation TR1602B or equivalent.
Refer now to FIG. 5, which is a more detailed schematic illustration of the
Line Control Group 41. The Line Control Group 41 is an assembly of Line
Control Units, as previously depicted in FIG. 3, each unit providing the
requisite control between an inlet telephone circuit and an outlet
telephone circuit via the Circuit Routing Matrix 51. As aforementioned,
the control is performed by a Microcomputer System 49 via a System Bus 90
in software selectable modes.
The line Control Unit is referred to in the preferred embodiment of the
present invention as an LT-610 Line Terminator. The unit consists of an
assembly of elements for the detection and control of analog and DC
signals on the trunk line. As aforementioned, the analog signals appear
across telephone circuit interface leads CT/CR; and the DC signals appear
between CBS1/CS and a signal common electrode.
As presented in FIG. 5, the interconnect between the inlet and outlet
telephone circuit is on the Line Control Unit via a Line Relay Group 411,
and then via the circuit Routing Matrix 51, as previously mentioned. The
Line Relay Group 411 employs Complementary-MOS (CMOS) analog switches and
dry reed relays for signal control. The CMOS elements used in the
preferred embodiment are commercially available RCA CD4016 units. They are
employed in the multiplexing of analog signals from the call progress tone
sources via Audible Tone Amplifiers 412 and from other analog inputs from
the Circuit Routing Matrix via Split Bypass Amplifier 413. The dry reed
relays employed in the preferred embodiment are commercially available
Struthers-Dunn MRRN Series Units. They are employed in the splitting of
the analog signal line between the analog multiplex bus and the inlet
signal pair CT/CR; in the splitting of the analog signal line between the
Circuit Routing Matrix inlet and the inlet signal pair CT/CR; and in the
individual breaking of the DC signal leads interconnected between the
Circuit Routing Matrix inlet and the inlet DC signalling pair CBS1/CS.
Further, as presented in FIG. 5, are the Line Control Unit elements for the
detection of analog and DC signals on the trunk line. These signals are
detected by sampling, via the Micro-Computer System application program,
the converted output of the Audible Tone Receiver 420 and the DC
signalling Buffer 419. The Audible Tone Receiver is an AM Detector, as is
well known in the art, and is designed for the detection of telephone
network type audible tone signals with protection against interference
from voice currents or other tone signalling systems; and the DC
Signalling Buffer 419 provides high to low level voltage conversion
between the trunk line interface CBS1/CS and the IC logic element
interface.
The logic elements requisite to the software selectable Line Control Unit
operation by the Micro-Computer System via the System Bus 90, consists of
Standard MSI, SSI and discrete units interconnected in a conventional
manner. As shown in FIG. 5, in the preferred embodiment, the decode
function 414 employs 74LS138 MSI logic elements; the output data bus
interface 415 uses F9334PC MSI logic elements and the input data base
interface 418 uses 74LS251 MSI logic element. In addition, to support the
duration of inputted audible tones, a cadence generator 416 makes use of a
74123 MSI logic element. Further, in the preferred embodiment, a
conventional analog application of operational amplifiers employing
Motorola MC1458V is used for the previously described amplifiers and
receivers, 412, 413 and 420.
Refer now to FIG. 6, which is a detailed schematic illustration of the
Circuit Routing Matrix 51. The Circuit Routing Matrix 51 provides
switching between an inlet telephone circuit via a unit in the Line
Control Group 41 and an outlet telephone circuit; between an inlet
telephone circuit via a unit in the Line Control Group 41 and a unit in
the Tone Transceiver Group 55; or between an inlet telephone circuit via a
unit in the Line Control Group 41 and both the outlet telephone circuit
and a unit in the Tone Transceiver Group 55. As aforementioned, the
switching is performed by a Microcomputer System 49, via a System Bus 90,
in software selectable modes.
The Circuit Routing Matrix 51 is referred to in the preferred embodiment of
the present invention as an assembly of RY-612 Matrix and a BD-611 Buffer
Decoder. The matrix unit consists of a sub-array, related axis drivers and
ordinate decoders. The Buffer Decoder unit consists of array decoders, a
switching timing circuit and the requisite logic interface with the System
Bus 90 for the control by the Microcomputer System 49.
As presented in FIG. 6, the previously described interconnect is by way of
a 4-Pole Non-Blocking Array 511. The defined array is obtained by
cascading standard units of commercially available matrices. The matrix
unit used in the preferred embodiment is a C.P. Clare Mini Memory Matrix
969A48A4B. A 4-pole crosspoint in the matrix is switched by Axis Drivers
512 which employ power transistor circuitry. FIG. 6A provides a discrete
component schematic illustration of the circuitry used in the preferred
embodiment to operate with the Clare Matrix, specifically identifying the
commercially available drive and power transistor employed.
The logic elements requisite to the software selectable Circuit Routing
Matrix operation by the Microcomputer System via the System Bus 90
consists of standard MSI and SSI units interconnected in a conventional
manner. As shown in FIG. 6, for the preferred embodiment, the output data
bus interface 514 uses 75LS174 MSI logic elements and the switching pulse
duration timing circuit 515 makes use of a 74123 MSI logic element.
Refer now to FIG. 5, which is a detailed schematic illustration of the Tone
Transceiver Group 55. The Tone Transceiver Group 55 is an assembly of
transceiver units, as previously depicted in FIG. 3. A transceiver unit is
used in the activation of the interconnect between an inlet telephone
circuit and an outlet telephone circuit via the Circuit Routing Matrix 51.
As aforementioned, the control is performed by a Microcomputer System 49
via a System Bus 90 in software selectable modes.
The Transceiver Unit is referred to in the preferred embodiment of the
present invention as an RS-618 Register/Sender. The unit consists of an
assembly of elements for the receiving and transmission of 2-of-8 tone
signals on the telehone circuit and the control of a dial tone on the
telephone circuit.
As aforementioned, the tone signals appear across telephone circuit
interface leads CT/CR and are transmitted to and from the transceiver unit
via the Line Control Unit and the Circuit Routing Matrix.
As presented in FIG. 7, the tone signals across the interface signal pair
between the Transceiver Unit and the Circuit Routing Matrix are passed to
a 2-of-8 Tone Receiver 556 via Input Amplifier 551 and Dial Tone Reject
Filter 553. Further, tones are passed to the interface signal pair from
the 2-of-8 Tone Encoder 557 via Low Pass Filter 554 and Output Amplifier
552 or are passed from the Dial Tone Bus via Switch 555, and output
Amplifier 552. The Receiver 556 detects the presence of valid high and low
band sinewaves used in tone dialing in the telephone network. The Filter
553 permits the detection of the 2-of-8 tones in the presence of a
conventional dial tone as is known in the art. The Encoder 557 digitally
synthesizes the high and low band sinewaves from an inputed 2-of-8 code.
The filter 554 removes unwanted frequency components from the signal
generated in the digital synthesization. The Input Amplifier 551, Output
Amplifier 552 and Low Pass Filter 554 are of conventio | | |
