Note: Descriptions are shown in the official language in which they were submitted.
FIELD OF THE INVENTION:
This invention relates to telephone systems
and in particular to a system for providing centrex
services and enhanced services to telephone sets which
would otherwise not be able to properly interface with a
centrex system or to use certain centrex services.
BACKGROUND TO THE INVENTION:
A centrex system which is connected to a
central office has long been known to provide PABX and
other types of features to subscribers. Typically there
is a separate subscriber line from the centrex system to
each telephone set. This provides non-blocking
capability. In order to utilize the centrex system,
specialized telephone sets are required which respond to
the specialized centrex supervisory signals and which
can transmit specialized supervisory signals to the
centrex system. Such specialized tel~phone sets are
therefore expensive.
If a group of subscribers wishes to have fewer
features, or more features than those provided by the
centrex system, yet to use the centrex system, this has
not been feasible, since it is expensive to provide
various grades of centrex telephone, and it has not
heretofore been possible to provide centrex lines with
service features more than those which are possible to
be provided by the centrex system.
SUMMARY OF THE PRESENT INVENTION:
In accordance with the present invention, a
system is provided for interfacing telephone sets with a
centrex system which always accesses the centrex
system. There is preferably one dedicated centrex
line for each telephone set, and thus there is no
blocking in the interfacing system. However the present
invention provides the means to drive a variety of
different telephone sets which have capabilities in
.. : .
. .
.
-2- 2~2~98
excess, or less than thoæe provided by the centrex
system, and those excess capabilities can be handled and
services provided by the present invention.
The capability of the present invention can
S be modified or defined by use of a plug-in read only
memory (ROM) cartridge, which cartridge can control the
capability of the present invention to operate
particular telephone sets. Therefore, for example, the
present invention can be utilized to interface a
capability tier of various digital telephone sets which
are available, e.y. from Mitel Corporation, for example
those having displays, those not having displays, those
having soft keys (having variable functions indicated on
a display), etc.
As a result, the present invention provides
increased flexibility to the user and substantially
reduced cost, since specialized expensive centrex
telephone sets need not be used, and the level sf
capability of centrex services may be invoked or changed
to a level desired by the customer, without reference to
the telephone company.
In addition, the present invention allows
inexpensive tip and ring 2500 type lines to be used
between the present invention and the centrex system,
yet high capability telephone sets can be used because
of the interpretation function to various supervisory
signals provided by the present invention.
The loop length of the present invention to
the centrex system may be e.g. 4-5 km, and an additional
loop length from the present invention to the telephone
set can be an additional 2-3 Xm. Thus a substantially
incxeased loop length may be used ov~r that of normal
centrex lines. Normal centrex lines have a limited loop
length of e.g~ 2-3 km, due to specialized line
interfaces required at the centrex and at the
, , - :: ;
- . : . :, ,., :,: . :;.. :,. ;
~, ;.~, , ~ ;
. : ~: :: . .
:: ::: : , : . .
-3- 2~2~
specialize.d centrex telephone sets, and high capability
(specialized) lines. The present invention therefore
increases the radius around the centrex systam in which
centrex services may be provided~
S In accordance with the present invention, a
system for interfacing telephone sets with a centrex
system is comprised of peripheral circuits for
interfacing telephone lines connected to telephone sets
and for interfacing csntrex lines, a set handler
connected to the peripheral circuits ~or connecting
individual telephone lines and individual centrex lines,
the set handler comprising apparatus for translating
supervisory and/or control signals received from the
telephone sets into supervisory and control signals of
types recognizable by the centrex system, whereby a
centrex call can progress as provided by the centrex
system.
Preferably each telephone set is assigned and
may be connected to a dedicated centrex line on a one to
one basis.
The set handler may be comprised of apparatus
for translating supervisory and/or control signals
received from the telephone sets and for providing
services to the telephone sets which are in addition to
or in substitution ~or those provided by the centrex
system in response thereto.
The present invention is pr~ferably comprised
of apparatus for translating supervisory and/or control
signals received from the centrex system and in response
providing services to the telephone sets which are
otherwise are not capable of being dealt with by the
telephone sets.
The present invention may be comprised o~
apparatus for translating supervisory and/or control
signals received from the centrex system and in response
.~:'. ` ` . ,: ~
, , ,:
" 20~2~98
-4-
for providing services to the telephone sets which are
in addition to or in replacement for those provided by
the centrex system.
BRIEF INTRODUCTION TO THE DRAWINGS:
A better understanding of the invention will
be obtained by reference to the detailed description
below, in conjunction with the following drawings, in
which:
Figure 1 is a basic block diagram of the
invention, and
Figure 2 is a more detailed block diagram of
the invention.
DETAILED DESCRIPTION OF THE INVENTION:
Turning to Figure 1, a centrex system 1 is
illustrated having various tip and ring lines 3, each of
which is destined for use with an individual telephone
set. These lines are terminated in an interface 5.
Subscriber lines 7 connect the interface to the
respective telephone sets 9. A ROM 11 is preferably
plugged into the interface 5, to define the
characteristic level or types of service to be provided
by interface 5.
In operation, a telephone set 9 will go off-
hook. The hook switch closure associated with the off-
hook condition is sensed in interface 5 and a
corresponding hook switch closure expected on a line 3
which is dedicated to that telephone set is transmitted
(appears on a line 3) to centrex 1 by interface 5 and is
sensed therein. The subscriber line is connected to the
centrex line 3. In return centrex 1 transmits dial tone
on that line 3, which is passed through int~rface 5 to
the telephone set 9 which has yone off-hook.
The subscriber which is associated with the
off-hook telephone set now dials for example a seven
digit number which is passed through to centrex 1.
~ . ..~ ::
;, : :.
:i.i `
-s- ~52~8
Interface 5 also monitors any signalling from the
telephone set 9 which i5 non-standard for the centrex.
For example, the centrex will normally provide a hold, a
conference call, or other services which are invoked by
signalling directly from the telephone set 9~ However
if the telephone set 9 provides a slgnal which is non-
standard from centrex 1, interface S will detect it and
replace it with the signal expected by the centrex 1.
This will often occur if the telephone set is not a
special centrex set.
Furthermore, interface 5 may provide services
not normally provided by centrex 1, for example a local
paging capability, the driving of soft keys including
labelling of particular pushbuttons on the telephone
sets on an associated display, etc. When a telephone
set generates command signals to invoke such services,
either automatically or upon a request for service
signal resulting from depression of a specialized or
predetermined pushbutton on the telephone set, interface
~0 5 can block those signals from being passed to the
centrex 1, and provides the service, e.g. by
transmitting control signals to the telephone set 9 and
centrex system. For example if a local page is to be
invoked, the interface should transmit a hold ~ignal to
the centrex causing the centrex to place a hold on the
line 3 and then it should connect the subscribar's
handset to a local paging amplifier.
The services which may be provided to the
subscribers can be defined and/or programmed in a plug-
in memory module ROM 11, which controls whichtranslation features and which level of service may be
provided. For example, if it is known that the
telephone sets 9 do nvt contain displays, ROM 11 will
control the interface 5 so that display control signals,
e.g. to display calling or called line numbers, or soft
,: ~
. .
-'', '~ : '
'., , ~',
key labels, are not generated and are not transmitted to
the telephone sets either from the centrex or from the
interface.
Figure 2 illustrates a block diagram of the
S invention. Each of the centrex lines 3 and subscriber
lines 7 is terminated in an appropriate line circuit,
shown as PIC (peripheral interface circuit) 13 or ~5
respectively. Each peripheral interface circuit can
contain several (e.g. four) line circuits, which provide
four wire pairs, i.e. four tip and ring lines to the
centrex system. The peripheral interface circuits 13
and 15 may be digital network interface circuits sold by
Mitel Corporation under the product number MT8972B,
described in the Mitel Digital Communications Handbook.
The peripheral interface circuits connect to
the input and output time-divided lines of time-and-
space division switch 17, referred to below as a DX
switch. This switch is described in U.S. Patent
4,510,597, issued April 9th, 1985, invented by Conrad
Lewis. A DX switch which can be used in element 17 is
sold by Mitel Corporation as the product type MT8980D or
as product type MT8981D, which are also described in the
aforenoted Handbook. In a successful prototype of the
invention, DX switch 17 had eight time divided input and
eight output lines (links), of which six of each were
connected to corresponding peripheral interface circuits
as shown in Figure 2. The remaining two input and
output links were allocated to common control.
Forty-eight ports were provided, with a
maximum capacity of 192 64 Kbps channels, providing a
bandwidth of 12 Mbps. Bandwidth allocation was fixed,
. ~
-
': ' ; ', : ` ; '., .~
: , :, :, : ,: , , :
:: .- : , -
:, :: . - , : : ~ :
,~ ,:, . :::
7 X0~2~98
with sixteen channels allocated to each peripheral
interface slot. The six periphsral links (each of which
involves an input and an output line of the DX switch
17) are distributed to the forty~eight ports, with
different ~rame pulses sent to each group of twenty-four
in order to split the bandwidth in halfO This allows
twenty-four ports to use all 12 Mbp3 of the bandwidth,
or 2 Mbps/slot if required.
The remaining two input and output lines of DX
switch 17 as noted above are allocated to common
control. An input line and an output line of the DX
switch are connected to an HDLC circuit 19, and an input
line and an output line of the DX switch are com~ected
to a digital signal processor circuit DSP 21. An ASIC
digital signal processor 21 generates signals and
decodes signals under control of microprocessor 29.
ASIC 23 is also connected to the HDLC circuit 19 and to
one of the common control lines of DX switch 17. Inputs
from the peripheral interface circuits are connected to
ASIC 23 and to phase locked loop 25.
Phase locked loop 25 receives timing
information from the interface circuits 13 receiving
digital signals from lines 3, and provides
synchronization signals to ASIC 23 for detection by
microprocessor 29. Microprocessor 29 can thus
synchronize outgoing siynals with those detected networX
signals.
Data and address buses 27 are connected to
ASIC 23. A microprocessor 29, preferably type 68000
available from Motorola, Inc., random access ~emory 31
and ROM 11 are connected to bus ~7. ROM 11 is connected
to the bus via an externally accessible connector. ROM
ll contains the programs accessed by microprocessor 29
in a well known manner to control operation of the DX
switch 17, digital signal processor 21, and ASIC 23. If
. . -, . .
,
: :
; not designated in another manner, ROM 11 contains a map
of correlation of centrex lines to designated subscriber
lines.
Operation of the circuit is as follows.
Assume that there is an incoming call from the centrex
system on a line 3. The line circuit in PIC 13 receives
ringing, which is detected and a ringing present signal
is sent via DX switch 17. Microprocessor 29, reading
the DX switch 17, recognizes that a ringing signal has
been received on a particular line, accesses a program
in ROM 11 and then sends a signal v.ia ASIC 23 which
decodes the latter signal, and sends a command signal to
DX switch 17 via the common control line to peripheral
interface circuit 13 to send a local ringing control
signal from DSP 21 to the designated, dedicated
telephone set connected to one of lines 7 for that
incoming line 3 via its associated interface circuit 15.
While other telephone sets can be used, it
will be assumed for this disclosure that the telephone
set used in MITELTM SUPERSET 420TM~
When the subscriber answers and goes off-hook,
this is detected in its associated line interface
; circuit 15, which sends an off-hook signal to HDLC l9,
which encodes it and sends a signal to microprocessor
29. Microprocessor 29 accesses a program in ROM 11 and
~ sends a control signal to the telephone set, which
:~ signal is decoded in HDLC 19 and is sent via the control
: input of DX switch 17 through the associated peripheral
interface 15 and line 7 to turn on the telephone set
microphone and earpiece. The microprocessor 29 also
sends a message to the peripheral interface 13
associated with the incoming line 3 to terminate the
,:~
TM - Trade Mark
~, '
- :: :. ; ~ - : . .
,, , . !, . . , ~ , , .
- 9 -
loop to the centrex system. This causes the ringing
signal at the centrex line to cease.
The microprocessor 29 then instructs the DX
switch 17 to connect a two way voice channel between the
S incoming line 3 and the called line 7. A voice or low
data rate data communication may now proceed.
If a subscriber, during the call, would like
to use a feature, he pushes a feature key or soft key on
his telephone set. The line 7 is monitored by the
interface circuit 15, and in a manner just described,
upon reception of the feature key or soft key switch
closure ox other signal the interface circuit 15 sends a
signal to HDLC 19 reflecting the operation of the
feature key, and the HDLC translates this into a code
understandable by microprocessor 29. The microprocessor
then determines the appropriate action.
For example, if a hold or call transfer is
desired, both of which can be effected at the centrex,
the subscriber pushes a hold or transfer key on his
telephone set. Since the key switch closure on the
telephone set is likely not the signal expected by the
centrex system since a non-centrex type phone is being
used, the microprocessor, receiving a message via the
HDLC that the particular feature or function is desired,
causes the correct signalling to be sent to the centrex,
e.g. a flash or a special DTMF code. ROM 11 carries a
table of conversion codes which is accessed by the
microprocessor 29 for the particular function requested.
Therefore, for example, if a subscriber pushes a key
that requests a service commanded by a signal that the
centrex expects as a flash, the microprocessor, in
accessing the table, receives a conversion code which is
an instruction to the interface 13 to perform a flash
tthe line 3 current is briefly broken).
.. :.
. . ~,: .
- lo-
The centrex system then responds by providing
the service, e.g. by placing a hold on the line,
transfer ring the line, etc. If the feature re~uest
command conversion in ROM 11 is such that the centrex
system 1 reyuires a DTMF code, the microprocessor 29
transmits a message, converted by ASIC 23, DSP 21 to
create appropriate DTMF tones, which pass under control
of microprocessor 29 through DX switch 17 into the
output channel leading to the interface circuit 13 which
is connected to the centrex line 3 in use.
The microprocessor 29 maintains track of each
call in RAM 31. Therefore if the telephone sets
connected in lines 7 have a display, such as the Mi-tel
Corporation digital SUPERSET 420TM telephone set,
microprocessor 29, using programs stored in ROM 11, can
provide command signals to the telephone set, using the
route and methods described above, so that a visual
display of the status of the call or a visual display of
the calling line number, or some other visual display is
provided to the telephone in use.
The centrex system sometimes applies special
ringing cadences, such as one long and three short
rings, etc. for certain groups of telephone sets, or for
certain purposes. The microprocessor 29 can detect and
decode this specialized ringing and can either cause the
telephone set to ring in the same cadence, or to merely
ring normally, or can provide a special message to the
telephone set display or cause the telephone set to
operate in a special manner. If, instead of ringing, a
tone signal is received from the centrex system,
microprocessor 29 decode the tone in a similar manner
described above provide information to the local
telephone set to which it is directed.
The centrex system usually can provide
services such as same number redial, redial busy
,
;
:
: :; : : ,
- .
~ .,
2~2~9~
subscriber, speed dial, etc. The present invention can
allow the subscribers connected to the present invention
to avoid invoking those services at the centrex system,
and to provide them instead. The m:icroprocessor 29 thus
S accesses programs in ROM 11 to cause the redial of
numbers which the microprocessor 29 has monitored as
having already baen dialed, and has stored in R~M 31
whereby a same number redial or redial busy subscriber
function may be invoked. Furthermore, RAM 31 can be
used to store speed dial numbers which are dialed by the
subscriber commanding them to be dialed by closing
specialized speed dial switches on the telephone set.
Indeed, the subscriber by dialing specialized codes can
store speed dial numbers at the centrex system, or at
the circuit just described in RAM 31, or at both.
Whether this or other features are provided
can depend on which operation programs are stored in
plug in ROM ll, which can be purchased by the usPr to
provide various grades of service. The present
invention can thus be specifically programmed to
interface different forms of centrex, or to provide
different features for different forms of centrex on a
telephone company by telephone company, feature group by
feature group basis.
It will be understood that the present
invention can be modified or expanded to interface
normal telephone switching systems rather than or in
addition to centrex systems, and with the addition of a
switching system responsive to dialed digits, be used as
a PABX or key telephone system.
Indeed, since the interface circuits 13 and 15
can communicate with the remainder of the circuit which
may be referred to as a control complex by means of
buses, the interface circuits may be grouped together
with a power supply and separated Erom the control
'
:. - : . '... ~ :
- ~
20~2~98
-12-
complex. Groups of peripheral circuits with associat~d
power supplies may be distributed around a building,
connected to a communication bus wh:ich terminates at the
control complex. This provides easy expandability of
S the system, and application to the particular
requirements of the particular group of sets of concern.
It will be recognized that the memory shown,
RAM 31, ROM ll, may be utilized in various forms. For
example, ROM ll may carry all of the normal operating
and normal feature control programs for microprocessor
29 and be permanently connected to bus 27, while an
auxiliary cartridge (not shown~ containing particular
special feature control programs may be plugged into bus
27. Alternatively ROM ll can carry the normal operation
programs for microprocessor 2g, a memory cartridge can
be plugged in to provide special feature programs, and
an additional application module can be added which
contains programs specialized for the particular
installation.
A person understanding this invention may now
conceive of alternative structures and embodiments or
variations of the above. All of those which fall within
the scope of the claims appended hereto are considered
to be part of the present invention.
.
: . .. .
~ : ,:
. ~
