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Claims  |
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We claim:
1. A communication switching system for establishing two-way communication
paths between a plurality of peripheral devices, said switching system
comprising: a common control, a plurality of highway pairs each having a
send highway and a receive highway, each of said send highways having one
end connected to said common control and each of said receive highways
having one end connected to said common control, means time dividing the
usage of said send highways and said receive highways into repetitive
frames each having a plurality of time slots including a plurality of
audio time slots, a plurality of peripheral devices associated with each
of said highway pairs, means in each peripheral device providing it with
sending access to one of the audio time slots of its send highway,
receiving control means in each peripheral device conditionally enabling
it to receive from at least one selected one of the audio time slots of
its receive highway, and means in said common control for forwarding the
signal appearing in each audio time slot of each of said send highways to
the corresponding audio time slot of any selected one or more of said
receive highways, each of said second highways including a communication
send line and a send clock line, each of said receive highways including a
communication receive line and a receive clock line, each of said
peripheral devices being connected to its communication send line for
sending access to its send highway and being connected to its
communication receive line for receiving access to its receive highway,
said means time dividing the usage of said send highways and said receive
highways into repetitive frames comprising means for injecting clock
signals onto said send clock lines and said receive clock lines, each of
said peripheral devices having a means connected to said send clock line
for timing its sending access to its communication send line, and each of
said peripheral devices having a means connected to its said receive clock
line for timing its receiving access to its communication receive line,
said means for injecting clock signals onto said send clock lines and said
receive clock lines comprising means for injecting send clock signals onto
said send clock lines at the ends thereof remote from said common control,
means in said common control for extracting the set of send clock signals
from said send clock lines and for mixing said set of send clock signals
to produce a single common clock signal, and a receive clock driver driven
by said common clock signal for producing a set of receive clock signals
injected respectively onto said receive clock lines at the ends thereof
adjacent said common control.
2. A communication switching system for establishing two-way communication
paths between a plurality of peripheral devices, said switching system
comprising: a common control, a plurality of highway pairs each having a
send highway and a receive highway, each of said send highways having one
end connected to said common control and each of said receive highways
having one end connected to said common control, means time dividing the
usage of said send highways and said receive highways into repetitive
frames each having a plurality of time slots including a plurality of
audio time slots, a plurality of peripheral devices associated with each
of said highway pairs, means in each peripheral device providing it with
sending access to one of the audio time slots of its send highway,
receiving control means in each peripheral device conditionally enabling
it to receive from at least one selected one of the audio time slots of
its receive highway, and means in said common control for forwarding the
signal appearing in each audio time slot of each of said send highways to
the corresponding audio time slot of any selected one or more of said
receive highways, said common control having for each of said send
highways a gating means in advance of said forwarding means operable in
response to a BLOCK signal associated with a given selected time slot to
inhibit transmission of signals appearing in such time slot to said
forwarding means.
3. A communication switching system as defined in claim 2 further
characterized by means for selectively providing each of said gating means
a sequence of BLOCK signals associated with a given time slot to cause the
transmission to said forwarding means in said given time slot a sequence
of bursts of signals spaced by absences of signals, and means in at least
one of said peripheral devices responsive to such spaced bursts of signals
for generating out-pulse dialing signals for transmission to an associated
trunk line.
4. A communication switching system as defined in claim 2 further
characterized by means for selectively providing each of said gating means
a sequence of BLOCK signals associated with a given time slot to inhibit
the transmission from the associated send highway to said forwarding means
in said given time slot during a given time interval, means operable
during said interval for transmitting dial tones to said forwarding means
in said given time slot, and means in at least one of said peripheral
devices responsive to said dial tones for transmitting said dial tones to
an associated trunk line.
5. A communication switching system as defined in claim 2 further
characterized by said plurality of time slots of each of said repetitive
frames also including a plurality of command time slots, a message sender
means associated with each of said highway pairs for injecting command
messages into said command time slots of its receive highway, means in
each of said peripheral devices for receiving command messages transmitted
on its associated receive highway and responsive to such command messages
for controlling on which of the audio time slots of its receive highway it
is to receive, a central processor for formulating the command messages
injected onto said receive highways by said message senders and for
providing instructions for controlling said forwarding means, at least one
tone decoder associated with each of said highway pairs, means in each of
said peripheral devices for generating dialing signals injected into its
associated audio time slot of said send highway, means operable to
temporarily assign said tone decoder to a peripheral device of the same
highway pair as said tone decoder during the times said peripheral device
injects dialing signals into its audio time slot of its send highway, said
tone decoder including means for producing a BLOCK signal associated with
the time slot to which said tone decoder is temporarily assigned for
transmission to the associated one of said gating means to inhibit
transmission of the signals appearing in said audio time slot to said
forwarding means, and said tone decoder including means for receiving the
dialing signals appearing in the audio time slot to which it is
temporarily assigned and for supplying dialing information derived from
said dialing signals to said central processor.
6. A communication switching system for establishing two-way communication
paths between a plurality of peripheral devices, said switching system
comprising: a common control, a plurality of highway pairs each having a
send highway and a receive highway, each of said send highways having one
end connected to said common control and each of said receive highways
having one end connected to said common control, means time dividing the
usage of said send highways and said receive highways into repetitive
frames each having a plurality of time slots including a plurality of
audio time slots, a plurality of peripheral devices associated with each
of said highway pairs, means in each peripheral device providing it with
sending access to one of the audio time slots of its send highway,
receiving control means in each peripheral device conditionally enabling
it to receive from at least one selected one of the audio time slots of
its receive highway, means in said common control for forwarding the
signal appearing in each audio time slot of each of said send highways to
the corresponding audio time slot of any selected one or more of said
receive highways, said plurality of time slots of each of said repetitive
frames also including a plurality of command time slots, a message sender
means associated with each of said highway pairs for injecting command
messages into said common time slots of its receive highways, means in
each of said peripheral devices for receiving command messages transmitted
on its associated receive highway and responsive to such command messages
for controlling on which of the audio time slots of its receive highway it
is to receive, a central processor for formulating the command messages
injected onto said receive highways by said message senders and for
providing instructions for controlling said forwarding means, each of said
peripheral devices having a number of different states, means in each of
said peripheral devices for varying its frame-by-frame pattern of the
sending of signals in its associated time slot of its send highway in
accordance with its state, and a status reporter associated with each of
said send highways, each of said status reporters having means for
determining the current status of each peripheral device connected to its
send highway by inspecting the frame-by-fram transmission pattern of each
audio time slot of such highway for use by said central processor in
formulating said command messages.
7. A communication switching system for establishing two-way communication
paths between a plurality of peripheral devices, said switching system
comprising: a common control, a plurality of highway pairs each having a
send highway and a receive highway, each of said send highways having one
end connected to said common control and each of said receive highways
having one end connected to said common control, means time dividing the
usage of said send highways and said receive highways into repetitive
frames each having a plurality of time slots including a plurality of
audio time slots, a plurality of peripheral devices associated with each
of said highway pairs, means in each peripheral device providing it with
sending access to one of the audio time slots of its send highway,
receiving control means in each peripheral device conditionally enabling
it to receive from at least one selected one of the audio time slots of
its receive highway, means in said common control for forwarding the
signal appearing in each audio time slot of each of said send highways to
the corresponding audio time slot of any selected one or more of said
receive highways, said common control having for each of said send
highways a gating means in advance of said forwarding means, said gating
means including means responsive to a BLOCK signal associated with a given
selected time slot to inhibit transmission of signals appearing in such
time slot to said forwarding means, at least one tone decoder associated
with each of said highway pairs, means in each of said peripheral devices
for generating dialing signals injected into its associated audio time
slot of its associated send highway, means operable to temporarily assign
a tone decoder to a peripheral device of the same highway pair as the tone
decoder during the times such peripheral device injects dialing signals
into its audio time slot of its send highway, said tone decoder including
means for producing a BLOCK signal associated with the time slot to which
it is temporarily assigned for transmission to the associated one of said
gating means to inhibit transmission of the signals appearing in said
audio time slot to said forwarding means, said tone decoder including
means for receiving dialing signals appearing in the audio time slot to
which it is assigned, each of said highway pairs having associated with it
at least one slot shifter, means in each of said slot shifters providing
it with sending access to one of the audio time slots of its send highway,
means in each slot shifter enabling it to be selectively assigned to
receive from any one of other auido time slots of its send highway and for
forwarding the signal which it so receives to the audio time slot to which
it is assigned for sending, and means for buffering the signals appearing
in the audio time slots of each send highway and for supplying such
buffered signals to all of the tone decoders and slot shifters associated
with such highway as the input send highway signals thereto.
8. A communication switching system for establishing two-way communication
paths between a plurality of peripheral devices, said switching system
comprising: a plurality of highway pairs each including a communication
send highway and a communication receive highway, means time dividing the
usage of said communication send highways and said communication receive
highway of said highway pairs into identical repetitive frames each having
a plurality of time slots including a group of audio time slots, said time
dividing means including a single master clock servicing all of said
highway pairs so that the repetitive frames of time slots for each of said
send highways are identical to and in phase with those of the other of
said send highways and so that the repetitive frames of time slots for
each of said receive highways are identical to and in phase with those of
the other of said receive highways, a plurality of peripheral devices
associated with each of said highway pairs, means in each peripheral
device providing it sending access to one of the audio time slots of its
send highway, receiving control means in each peripheral device
conditionally enabling it to receive from at least one selected one of the
audio time slots of its receive highway, a switch associated with each of
said highway pairs of said switches having an output terminal connected to
said receive highway of its highway pair and also having a plurality of
input terminals, means connecting all of said send highways individually
to corresponding ones of said input terminals of each of said switches
whereby each of said switches receives the signals appearing on all of
said send highways, and switch control means for controlling each of said
switches whereby during each of said time slots either a selected one or
none of its said input terminals is connected to its said output terminal.
9. A communication switching system as defined in claim 8 further
characterized by said plurality of time slots of each of said frames also
including a group of command time slots, means in each of said peripheral
devices causing it to continuously receive the signals transmitted in said
command time slots of its said receive highway, a message sender means
associated with each of said highway pairs for injecting command messages
into said command time slots of its receive highway each of which messages
is addressed to a selected one of said peripheral devices associated with
said receive highways and instructs such selected peripheral device on
which of said audio time slots of said receive highway to receive, and
said receiving control means of each of said peripheral devices including
means responsive to the command messages addressed to it to cause said
peripheral device to receive on the audio time slot of its receive highway
as instructed by said command messages.
10. A communication switching system for establishing two-way communication
paths between a plurality of peripheral devices, said switching system
comprising: a plurality of highway pairs each including a communication
send highway and a communication receive highway, means time dividing the
usage of said communication send highways and said communication receive
highway of said highway pairs into identical repetitive frames each having
a plurality of time slots including a group of audio time slots, a
plurality of peripheral devices associated with each of said highway
pairs, means in each peripheral device providing it sending access to one
of the audio time slots of its send highway, receiving control means in
each peripheral device conditionally enabling it to receive from at least
one selected one of the audio time slots of its receive highway, a switch
associated with each of said highway pairs each of said switches having an
output terminal connected to said receive highway of its highway pair and
also having a plurality of input terminals, means connecting all of said
send highways individually to corresponding ones of said input terminals
of each of said switches whereby each of said switches receives the
signals appearing on all of said send highways, switch control means for
controlling each of said switches whereby during each of said time slots
either a selected one or none of its said input terminals is connected to
its said output terminal, a means providing a plurality of supervisory
tone signals on a corresponding plurality of supervisory tone lines, and
means connecting all of said supervisory tone lines individually to
corresponding ones of said input terminals of each of said switches
whereby each of said switches also receives all of said supervisory tone
signals so that under control of said switch control means each of said
switches may be set during each of said time slots to supply to its said
output terminal either the signal then appearing on any selected one of
said send highways, the signal appearing on any selected one of said
supervisory tone lines, or no signal. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to communication switching systems for selectively
establishing two-way communication paths between desired ones of a set of
telephone instruments, trunk line interfaces or other two-way
communication peripheral devices, and deals more particularly with such a
switching system of the type commonly referred to as a private automatic
branch exchange (PABX) for servicing a reasonably large number of
telephone instruments or other two-way communication peripheral devices,
for example up to several hundred of such devices, such as those used in a
given office, factory, government agency or similar business
establishment.
The communication system of this invention is in many respects similar to
that disclosed in copending U.S. patent application Ser. No. 665,551,
filed Mar. 10, 1976. The communication system of that application is one
using time division multiplexing for the transmission of signals on the
communication lines and has a processor implemented common control.
Further, the system disclosed in the application may be said to be one
having, for the transmission of signals between peripheral devices, a
single highway pair consisting of a single send highway to which the
peripheral devices have sending access and a single receive highway to
which the peripheral devices have receiving access. In such system, the
number of peripheral devices is limited by the number of time slots made
available by the multiplexing format. In the particular system shown by
the application a maximum of 50 two-way communication peripheral devices
can be serviced.
The general object of this invention is to provide a communication
switching system comprised of a number of highway pairs, each generally
similar to the single highway pair of the aforesaid patent application,
whereby an increased number of peripheral devices may be included in the
system.
Another object of this invention is to provide a communication switching
system of the foregoing character whereby the size of the system, measured
by peripheral device capacity, is flexible and may be readily varied
incrementally by varying the number of highway pairs included in the
system.
A still further object of the invention is to provide a multiple highway
communication system which utilizes many of the same components as the
single highway pair system of the aforesaid patent application and which
system has or is capable of having the same desirable features as said
single highway pair system, these features including a low per station
cost for the system, ease in installing and maintaining the system, speedy
operation in setting up and disconnecting communication paths and handling
other services requests, and the ability to provide various different
system functions, such as camp-on, call forwarding, call conferencing,
call hold, etc. largely through programming of the processor memory and
without the need for keys on the telephone instruments.
Other objects and advantages of the invention will be apparent from the
drawings and from the following detailed description and claims.
SUMMARY OF THE INVENTION
This invention resides in a PABX communication system using time division
multiplexing over multiple transmission highways for establishing two-way
communication paths between a plurality of telephones, trunk line
interfaces or similar two-way communication peripheral devices. Each
broadly defined transmission highway is a highway pair made up of a send
highway and a receive highway servicing an associated group of peripheral
devices each having sending access to its send highway and receiving
access to its receive highway for communication with the system. One end
of each send highway and one end of each receive highway is connected to a
processor implemented common control. The multiplexing format of all
highways of the system is the same and consists of repetitive frames each
having a fixed plurality of time slots most of which are "audio" time
slots and a few of which are "command" time slots. Each peripheral device
has sending access to a particular one of the audio time slots of its send
highway and includes means enabling it to receive on any selected one or
more of the audio time slots of its receive highway.
The switching required for establishing two-way communication paths is
carried out in part in the peripheral devices and in part in the common
control. The switching performed in the peripheral devices consists of
conditioning, by way of command messages transmitted to it over the
associated send highway in the command time slots, a peripheral device to
receive on a particular audio time slot or slots of its receive highway.
The part of the switching which occurs in the common control is performed
by a plurality of highway switches, one for each highway pair, which under
processor control route signals appearing in one audio time slot of one
send highway to the corresponding audio time slot of the receive highway
or highways associated with the peripheral device or devices intended to
receive such signals.
The invention further resides in the common control including slot shifters
associated with each highway pair for shifting a signal appearing in one
audio time slot of one send highway to another audio time slot of that
highway in the event the corresponding time slot of the receive highway to
which the signal is to be forwarded is already in use. It further resides
in the use of tone decoders, gating repeaters and dual tone multiple
frequency (DTMF) generators for effecting either outpulsing from a
peripheral device associated with a dial pulse trunk line or touch tone
outputs from a peripheral device associated with a touch tone trunk line.
A further aspect of the invention resides in a supervisory tone generator
in the common control which supplies supervisory tones to each of the
highway switches whereby each highway switch may also be set to supply,
under processor control, any selected one of the supervisory tones to any
one of the audio time slots of the receive highway with which it is
associated. Also, each peripheral device includes a means for varying its
frame-by-frame transmission pattern in accordance with its state, and each
highway pair includes a status reporter which inspects the transmission
pattern from each audio time slot of its associated send highway and
furnishes status information so obtained and concerning each peripheral
device to the processor for use in establishing and disestablishing
communication paths.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram showing broadly a complete
communication system embodying this invention.
FIGS. 2a, 2b, 2c, 2d, 2e and 2f when arranged relative to one another as
shown in FIG. 3, form a single diagram, hereinafter referred to as FIG. 2,
showing in greater detail the communication system of FIG. 1.
FIG. 3 is a diagram illustrating the manner in which FIGS. 2a to 2f are
arranged to form FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The general organization of a system embodying this invention is
exemplified by the system illustrated broadly in FIG. 1. Referring to this
figure, the illustrated system includes three highway pairs A, B and C
each servicing up to forty-six two-way communication peripheral devices
10, 10, the devices of highway pair A being designated A0 to A45, those of
highway pair B being designated B0 to B45 and those of highway pairs C
being designated C0 to C45. The number of highway pairs in a given system
may, however, vary without departing from the invention, it indeed being a
feature of the invention that the size of the system may be readily varied
by changing the number of highway pairs it contains. Also, the maximum
number of peripheral devices which each highway pair can service may vary
depending on the number of audio time slots provided in the multiplexing
format, and not all possible peripheral devices need be installed.
Each highway pair consists of a send highway and a receive highway
identified as shown in FIG. 1. Each peripheral device 10 of a particular
highway pair is connected to its send highway for sending access to the
system and is connected to its receive highway for receiving access to the
system. One end of each send highway and one end of each receive highway
is connected to a common control 12 and the opposite ends of each highway
are connected to a master clock and termination unit 14. Signals on the
send highways are transmitted inwardly toward the common control 12 and
signals on the receive highways are transmitted outwardly from the common
control, as indicated by the arrows in FIG. 1.
The master clock and termination unit 14 suitably terminates the adjacent
ends of the send and receive highways and supplies an identical clock
signal to all send highways to time divide the usage of the send highways
into repetitive frames of time slots according to the multiplexing scheme
used for transmission. In the common equipment 12, these clock signals are
received, regenerated and supplied to the receive highways for similarly
time dividing the usage of the receive highways.
Although a peripheral device sends on its send highway and receives on its
receive highway, the signals which it receives do not necessarily
originate on its send highway. For example, if device A1 wishes to send a
message to device B2, the signals which device A1 injects on send highway
A must be forwarded to receive highway B in order to reach device B2. As
described in more detail hereinafter, an important function of the common
equipment 12 is to achieve such forwarding of signals from the send
highways to the receive highways.
FIG. 2 shows in more detail the system of FIG. 1. Before considering this
figure in depth, it should be noted that the illustrated system is an
expanded version of the single highway pair system shown and described in
the aforementioned patent application Ser. No. 665,551. In particular, the
time division format, the nature of the individual send and receive
highways, the method of signal injection and extraction to and from the
highways, the construction of the peripheral devices (referred to as line
appliques and trunk appliques in the previous application) and the
construction and arrangement of many other parts of the system are similar
to that of the disclosure of the aforementioned application, and reference
may be had to said application for further understanding of these matters.
The time division format used in the system of FIG. 2 is identical with
that of the aforementioned application and involves a fifty-six time slot
commutation frame having a frame rate of 12.5KHz. Timing is provided by a
clock generating pulses at a rate of 700KHz. Synchronism is achieved by
dropping every fifty-sixth pulse from the stream of clock pulses to
establish the commutation frame rate. The dropped pulse is regenerated in
the peripheral devices and elsewhere locally as a sync pulse when needed.
The fifty-six pulses of each frame divide time into fifty-six time slots
for each frame. Four of these are "command" time slots used to transmit
command messages to the peripheral devices, one is a "sync" time slot
which is not used, and another is a "quiet" slot which carries an
unmodulated signal. During dialing, for example, a subscriber hears
nothing because his peripheral device is conditioned to receive on the
quiet slot at that time. The remaining fifty time slots, 0, 1, 2, . . .
49, are "audio" time slots which are used for talking paths between the
peripheral devices.
The command time slots convey digital information by way of pulses which
may or may not be present. A pulse appearing in a command time slot
represents a "logical 1" and the absence of a pulse represents a "logical
0". Each command message is made up of a sequence of logical 1's and 0's
transmitted during a number of consecutive commutation frames. Audio or
voice-band information is in turn carried by width modulated pulses in the
audio time slots. When a particular audio time slot is not in use, no
pulse appears in it as it is repeated in consecutive frames.
Referring to FIG. 2, each send highway is comprised of two transmission
lines, one being a "send" line on which the audio and command message
signals are transmitted and the other being a "clock" line used for timing
the sending access of the associated peripheral devices to the send line.
For the three illustrated highway pairs, the send lines are indicated at
SNDA, SNDB and SNDC, the three clock lines are indicated at SCLKA, SCLKB
and SCLKC. Similarly, each receive highway is comprised of two
transmission lines, one being a "receive" line over which the audio and
command message signals are transmitted and the other being a "clock" line
for timing the receiving access of the associated peripheral devices to
the receive lines. In the illustrated case, the three receive lines are
designated RCVA, RCVB and RCVC and the three associated clock lines are
designated RCLKA, RCLKB and RCLKC. Also, as explained in the
aforementioned patent application, each line is actually a two conductor
balanced line with all of the transmitted signals being balanced ones.
The master clock and termination unit 14 includes a master clock 16 which
produces clock pulses at the desired 700KHz rate. These pulses are
delivered to a sync pulse dropper circuit 18 which drops every fifty-sixth
pulse in the stream of clock pulses from the clock 16 to signal the
beginning and end of each commutation frame. The pulses from the pulse
dropper 18 are in turn supplied to a send clock driver 20 which supplies
three pulse trains, identical to that from the pulse dropper 18, to the
three send clock lines, SCLKA, SCLKB and SCLKC. A receive end termination
circuit 21 provides suitable terminations for the adjacent ends of the
receive and receive clock lines of the three receive highways. Similarly,
a sending end termination circuit 22 provides suitable termination for the
adjacent ends of the send lines of the send highways. The circuit 22 also
injects on each send line an unmodulated pulse in the quiet slot of each
frame with such quiet slot pulse being produced by a quiet slot pulse
generating circuit 24 having as an input the pulse train emanating from
the sync pulse dropper 18.
Included in the mix of peripheral devices serviced by the system of FIG. 2,
is a console including a telephone and also including a busy lamp field
and other features not available at other peripheral devices servicing
telephones or trunks. Two-way communication between the console and a
central processor 32 in the common control, to convey data required by the
special console features, is provided by a two-way data bus 28. With the
exception of this console connection to the common control, all other
peripheral devices communicate with the remainder of the system only
through the send and receive highways. In a typical installation, most of
these other peripheral devices are ones serving telephone instruments and
others are ones serving as interface units with trunk lines such as
indicated at 30, 30.
As exemplified by the peripheral device A1, each such device has one
terminal 32 for sending access to its send line and another terminal 34
for deriving clock pulses from its send clock line for timing the sending
access. Further, a terminal 36 provides receiving access for the
peripheral device to its receive line with such receiving access being
timed by clock signals supplied through another terminal 38 connected to
the associated receive clock line.
The common control 12 is controlled by a stored program central processing
unit 32 having an associated system memory 34 which stores the operating
program for the processor and data needed for functioning of the system.
For each highway pair, the illustrated common control includes four slot
shifters 26, 26, four tone decoders 36, 36, a single status reporter 38, a
gating repeater 40, a dual tone multiple frequency (DTMF) generator 42 and
a highway switch 44. Each gating repeater 40 has as inputs thereto the
send and send clock lines of its associated send highway. Other inputs are
a BLOCK signal appearing on an input line 46 and pulses, modulated by
touch tone signals, appearing on an input line 48 and produced by the
associated DTMF generator 42. The outputs from each gating repeater 40 are
two internal highways 50 and 52. The internal highway 50 is referred to as
a buffered send highway consisting of a buffered send line 54 and a
buffered clock line 56, the signals appearing on these lines being
buffered versions of the signals received by the gating repeater from the
associated input send and send clock lines. The internal highway 52 is
referred to as a gated send highway and consists of a gated send line 58
and a gated clock line 60. The signals appearing on the gated send line 58
are a buffered version of the signals appearing on the associated input
send line except that the repeater includes a gate between the input send
line and the gated send line which gate in response to the appearance of
BLOCK signals appearing on the line 46 in any given time slot inhibits or
blocks transmission of signals to the gated send line in that time slot.
When BLOCK signals do appear in a particular time slot, signals appearing
on the associated tone line 48 may be injected through the gating repeater
into the corresponding time slot of the gated send line. The gated clock
line receives clock signals which are a buffered version of the signals
appearing on the input send clock line. These clock signals are not gated
or inhibited by the BLOCK signals appearing on the line 46 but do pass
through the same type of circuitry as the send line signals so as to be
subject to the same time delays, distortions, etc. as the send line
signals.
To provide timing or clock signals for the receive highways and for various
components of the common control, the common control also includes a clock
mixer 62 having as inputs thereto all of the gated clock lines 60. This
mixer, from the input clock signals, produces an output clock signal,
referred to as "common clock", on the line 64. This common clock signal is
synthesized or regenerated from the several inputs to the clock mixer so
as to be the "best average" of the input signals and of essentially the
same nature as any one of them. The common clock signal on the line 64 is
in turn supplied to a receive clock driver 66 which generates three
identically corresponding clock signals delivered to the three receive
clock lines.
Each highway switch has an output terminal connected to the receive line
(RCVA, RCVB or RCVC) of its associated receive highway. It further has
three input terminals connected respectively to the three gated send lines
58, 58. Four other input terminals of each highway switch are also
individually connected to four supervisory tone lines 68, 70, 72 and 74 on
which appear, in each time slot, pulses width modulated by "reorder",
"busy", "ring" and "dial" tones and which are provided by a supervisory
tone generator 76. During any time slot each highway switch may be set to
connect its output terminal to any selected one or none of its input
terminals. Accordingly, during any time slot, the switch may be set to
pass ot its output terminal and to the associated receive line the signal
then appearing on any one of the gated send lines 58, 58, the signal
appearing on any one of the supervisory tone lines 68, 70, 72 and 74 or no
signal. The setting of the switch points of each highway switch during
each time slot is controlled by a switch control unit 78, one for each
switch, which supplies switch point setting signals to the switch through
a set of terminals 80. The switch control unit 78 is responsive to a set
of instructions, each identifying the switch setting for one time slot,
stored sequentially in an associated fifty-one word memory 81. The
fifty-one words or instructions stored in the memory 81 specify the switch
point settings during each of the fifty audio time slots and the quiet
time slot, and the contents of the memory are updated as required by the
CPU over the data bus 28.
Under control of a memory read control unit 82 and clock signals supplied
by the common clock line 64 during each time slot, a switch setting
instruction is read from each memory 81 during each audio time slot and
each quiet slot and is supplied to an associated latch 83 from which it is
in turn supplied to the switch control unit 78 for conversion to proper
switch setting signals on the lines 80. A highway switch does not forward
any signals during the command time slots of each frame, and therefore
during this portion of each commutation frame, no instructions need be
drawn from the associated memory 81. The switch memory includes a separate
buffer register into which the CPU, over the data bus 28, may enter a time
slot identifying number and a switch point instruction word. The time
interval occupied by the command time slots is, therefore, utilized for
inspection of the buffer register and for memory update if the buffer
register is found to hold new information.
Every two-way peripheral device 10 is assigned to a particular highway pair
and is also assigned a particular audio time slot. The assigned
highway/time-slot combination is therefore unique to that peripheral
device. For example, in FIG. 2 the highway assignment of each peripheral
device is identified by the letters A, B and C and its time slot
assignment is identified by the numbers 0 to 45 so that, for example, the
peripheral device identified as "B1" is assigned to highway B and audio
time slot 1.
All transmission from a two-way peripheral device is on the send highway of
its assigned highway pair, and during its assigned time slot. When there
is no transmission from a particular two-way peripheral device there is no
signal in the time slot assigned to that device on its send highway.
Further, all reception by a peripheral device is from the receive highway
of its assigned pair. The device receives all command messages which
appear on that receive highway (and which are transmitted by signals
appearing in the command time slots) but disregards messages not
specifically addressed to it. Each peripheral device has a means enabling
it to selectively receive during the fifty audio time slots and the quiet
slot, with the particular slots on which it is to receive being specified
by the command messages addressed to it. It may, therefore, be directed by
a command message to receive (from the receive highway of its assigned
highway pair) during any of the fifty audio time slots and quiet slots in
each commutation frame, or during none.
A one-way talking path from one peripheral device to another, for example
from port A1 to port B1, is established by two commands from the processor
32. First, the highway switch 44 which serves receive highway B is
instructed by the CPU to close the switch point to A1's send highway
(actually gated send highway A) during device A1's assigned time slot.
That is, highway switch B is instructed, during time slot 1 to close the
switch point connecting gated send line A to receive line B so that the
signal appearing in time slot 1 of send line A is forwarded to time slot 1
of receive line B. Secondly, device B1 is instructed by the CPU by way of
command messages sent on receive highway B to receive during port A's
assigned time slot, that is time slot 1. It should be noted here that the
signal which is transmi | | |
