Note: Descriptions are shown in the official language in which they were submitted.
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01 This invention relates to a trunk circuit control system,
02 and in particular to a distributed control system which minimizes
03 the number of conductors interconnecting the trunk circuits with
04 the remainder of the telephone switching system.
05 Telephone switching systems such as PBXs utilize various
06 kinds of trunk circuits, such as outgoing trunks, incoming
07 trunks, special service trunks, etc. In addition, such trunk
08 circuits often utilize special outpulsing circuits, timing cir-
09 cuits, signal modification circuits for filtering spurious line
signals, control circuits, etc.
11 In a system such as an electronic PBX, typically a stored
12 program computer i5 utilized to control various functions of its
13 operation. In such a case each of the trunk circuits is
14 connected to the computer data and address bus, for instance by 8
individual conductors. In addition, each trunk circuit has
16 connected to it power supply conductors, signal carrying
17 conductors, and other intertrunk or intercircuit conductors.
18 Clearly the number of conductors to be connected to a single
19 trunk circuit is fairly large. With PBXs becoming physically
smaller and smaller as the size of the individual electronic
21 components used therein are miniaturized and integrated, the
22 physical size of the interconnecting backplane becomes one of the
23 major factors limiting the the size efficiency of the apparatus.
24 In addition, it will be recognized that due to the
requirement for different kinds of trunks as noted above, their
26 control and signal processing features are usually sufficiently
27 different that each kind has its own unique design. Further,
28 while the internal design of the switching system is usually
29 carefully controlled, exterior circuits which interface the
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01 trunks are subject to sometimes uncontrolled forces, such as
02 weathering, the induction of common mode signals, random noise
03 spikes, dropouts etc. Accordingly trunk circuits are often
04 specially designed and optimized to function with existing trunks
05 which are subject to the aforenoted hostile forces, and thus
06 different kinds of trunk circuits have different and special
07 designs for specialized use in such a system.
08 For the above reasons, and due to the physical design of
09 the system, usually a predetermined maximum number of trunks of a
particular kind can be used in a PBX. Printed circuit boards
11 carrying certain special trunk circuits are disposed in one
12 physical location and are usually wired into the PBX system with
13 minimum expansion capability. Furthermore, due to the extensive
14 wiring required in the PBX, the total number of trunk circuits
used is limited by the speed of operation of the bus for a given
16 address and data bus, and is limited by the length of the bus.
17 Furthermore, the larger the number of wires interconnecting the
18 trunk circuits, the more probability there is for crosstalk to
19 occur, as the wires must increasingly run close together.
The present irlvention, on the other hand, reduces substan-
21 tially the length and size of the backplane of a PBX. The above
22 i8 achievable by utilizing a distributed control system, by which
23 an individual microprocessor with associated memory is physically
24 located on a printed circuit board with one or more of the
trunk circuits. An electronic signal, stored in an
26 interchangeable memory of the microprocessor causes the
27 microprocessor to operate each of the associated trunks as a
28 particular predetermined kind of trunk.
29 The result of this is to minimize substantially the back-
plane communication requirements between the main PBX control
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01 processor and each of the printed circuit boards carrying the
02 trunks, since communication is restricted to that required be-
03 tween the main PBX control processor and each of the microproces-
04 sors. Since the main communication bus to the trunk printed
05 circuit boards is thus physically minimized, substantial increase
06 in the number of trunk-carrying printed circuit boards which
07 might be used in the PBX is facilitated, thus allowing an
08 economical scale up to a large size PBX, for instance of up to
09 2,000 lines, in a small console, for what is believed to be first
time.
11 Furthermore, since the determination of each kind of trunk
12 i8 based on stored signals or the equivalent in the microproces-
13 sor memory, and since each of the trunk printed circuit boards is
14 otherwise identical physically to each of the others, it is a
simple matter to change the quantities of the different kinds of
16 trunks at will, simply by changing a plug-in trunk module in the
17 printed circuit board and the signal content of the ;
18 microprocessor memory. Accordingly the PBX capability can be
19 expanded, contracted or varied according to the needs of the PBX
user with little difficulty.
21 Since all of the printed circuit boards which carry the
22 trunk circuits are identical, the cost of production thereof is
23 reduced due to the economics of scale. The telephone company
24 stocking requirements for replacement trunk circuit printed
circuit boards is simplified, since only a single standard trunk
26 circuit printed circuit board need be stocked.
27 The invention is, in general, in a telephone switching
28 system which utilizes central processor operated trunk circuits,
29 a printed circuit board, a microprocessor including a memory,
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01 apparatus for connecting a plurality of trunk circuits in a
02 standard and similar manner to the microprocessor on the printed
03 circuit board, a switching system control processor for operating ;:
04 the microprocessor, and a data and an address bus interconnecting
05 the central processor and the microprocessor. This results in
06 the number of conductors connecting the printed circuit board
07 being no greater than would be required for a single trunk
08 circuit, and substantially reduces the number of conductors
09 connected to the buses over the number which would be required if
a plurality of trunk circuits were all connected to the bus
11 system as in the prior art.
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01 As was noted above, a predetermined signal stored within
02 the memory means causes the microprocessor to operate
03 interchangeable trunk circuits as predetermined types of trunks.
04 It should be noted that when referring to a signal stored within
05 the memory means, it is intended that this can include a variety
06 of storage modes, such as the use of a read-only memory (ROM),
07 which stores information by the use of blown fuse interconnection
08 patterns, by the use of permanently stored charges which are
09 alterable by the use of ultraviolet light, etc. In this respect
the memory acts similarily to a plug patchboard with an
11 interconnection pattern of wires which causes the microprocessor,
12 upon accessing the memory, to utilize a particular subroutine
13 which may be standard for particular trunks connected thereto.
14 A better understanding of the invention will be obtained
by reference to the single drawing, and to the description below.
16 The single drawing is a block diagram of the apparatus of the
17 invention.
18 In the preferred form of the invention, a switching system
19 such as a PBX has a multiplicity of printed circuit boards 1,
each carrying a plurality of trunk circuits 2. A microprocessor 3
21 is physically located on each of the printed circuit boards.
22 Each microprocessor is connected in a similar manner to the trunk
23 circuits 2 which it is to control. A memory 4, preferably
24 interchangeable, is associated with each microprocessor. Each
microprocessor is connected via a board-edge connector (not
26 shown) to a data bus 5 and to an address bus 6, which buses are
27 both connected to a control processor 7.
28 It should be noted that in the absence of microprocessor
29 3, with four trunk circuits per printed circuit board, and util-
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01 izing an 8 bit control processor, each printed circuit board
02 would have at least 32 terminals, with the accompanying complex~
03 ity of conductor junctions in the PBX interconnection backplane.
04 In the present invention, connection of each printed circuit
05 board requires only 8 terminals for address and data, a reduction
06 of 75%.
07 Further, in the aforenoted prior art system, for a given
08 number of instructions to be transmitted to and received from
09 each trunk circuit by the central processor, either an extremely
fast control processor or a large bus must be utilized. In one
11 case, a high operation speed of the control processor must be
12 utilized in order to access the large number of trunks, which in-
13 crea~e its vulnerability to crosstalk, while in the large bus
14 type of system, the backplane of the PBX becomes excessively com-
plex and large.
16 On the other hand, in the present invention the processing
17 logic is distributed. A minimal size of bus between the control
18 processor and the distributed microprocessors need only be used.
19 Furthermore, the microprocessors need only be accessed by the
system control processor at considerably less frequent intervals
21 than would be the case for each of the trunks, since the micro-
22 processors themselves contain, with their memories, sufficient
23 control capability for the trunks, and do not require the con-
24 stant control as do the trunks themselves. The communication
link between the control processor and each of the microproces-
26 sors is thereby substantially simplified, as is the physical
27 interconnection pattern of the backplane. The likelihood of ;^
28 crosstalk is thereby reduced, and the required speed of the main
29 control processor is also reduced.
Further, for a given physical size of PBX, the number of
31 trunks which can be accommodated is substantially increased since
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01 the backplane is simplified, for reasons which will be
02 explained below.
03 Special kinds of trunk circuits are used for different
04 applications, for instance to handle incoming calls, outgoing
05 calls, etc. In the present invention the connection pattern for
06 each of the trunk circuits 2 is identical to all of the others.
07 Each of the four trunks on each of the printed circuit boards is
08 connected to the corresponding microprocessor 3 in a standard and
09 identical manner.
; 10 Since each of the printed circuit boards is identical,
11 clearly the cost of the trunk circuits is substantially reduced
12 due to the economies of scale of manufacture, standard component
13 purchase requirements, standard stocking requirements for all of
14 the trunk circuit boards, etc.
The trunks are distinguished in their operation under di-
16 rect control of the individual microprocessors. Each of the
17 memories 4 is intended to store data which causes the
18 microprocessor to operate each of the individual trunk circuits
19 in a predetermined fashion. For instance, certain trunk circuits
plugged into a printed circuit board can be operated as incoming
21 trunk circuits, others as outgoing trunk circuits, etc. The
22 memory 4 can be a read-only memory (ROM), a nonvolotile random
23 access memory (RAM) etc. according to choice of the designer.
24 This memory acts as the equivalent of a plug patchboard, for
causing the microprocessor to operate each of the trunk circuits
26 2 in a predetermined manner.
27 As a result the functions of the trunk circuits can be
28 mixed, and they need not be located at physically predefined lo-
29 cations to accommodate external wiring as was necessary in the
prior art. Furthermore, the numbers and mix of different kinds
31 of trunks can be changed at will, merely by changing the ROM, or
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01 by changing the ROM interconnection pattern (i.e. by ultraviolet
02 erasing and reestablishing it using a different memory pattern).
03 Since the connector wiring locations at the backplane of the PBX
04 for individual printed circuit boards carrying different kinds of
05 special trunks are now always the same, in contrast to prior art,
06 the numbers and kinds of trunk circuits are expandable to the
07 maximum physical limits of the PBX cabinet. Substantially
08 increased versatility, and reduced cost of manufacture is thus
09 obtained.
In addition, since prewired but unfilled racks ready for
11 expansion to accommodate specific types of trunk circuits ~
12 are not required in the present invention, but only trunk circuit ;
13 sockets on standard and identical printed circuit boards, more
14 trunk printed circuit boards holding more trunks can be
accommodated in a given space than the prior art system. In the
16 alternative, the physical size of the PBX can be reduced.
17 Furthermore, in case of the discovery of a faulty trunk
18 circuit, the control processor 7 need only transmit a signal to
19 the microprocessor associated with the faulty trunk to busy it
out or otherwise mark the trunk as being unuseable. In the event
21 this causes intolerably decreased traffic handling capability of
22 the remainder of the trunks which are similar to the one which is
23 faulty, a spare trunk can be activated easily under control of
24 the microprocessor to substitute for the faulty trunk.
Substantially increased redundancy, and therefore increased
26 reliabilty of the PBX is thus achieved.
27 The embodiment shown in the drawing utilizes four trunks
28 on a printed circuit board; the invention should not be
29 considered as being limited thereto, since the number of trunks
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01 on a printed circuit board is limited only by the capability of
02 the associated microprocessor and memory which are mounted
03 physically on the same printed circuit board, and by the
04 capability of the printed circuit board to physically accommodate
05 a given number of trunks.
06 A person skilled in the art of understanding this inven-
07 tion may now conceive of various modifications and alternatives.
08 All are considered within the sphere and scope of this invention
09 as defined in the appended claims.
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