CA1185024A - Signalling in pbx systems - Google Patents
Signalling in pbx systemsInfo
- Publication number
- CA1185024A CA1185024A CA000386626A CA386626A CA1185024A CA 1185024 A CA1185024 A CA 1185024A CA 000386626 A CA000386626 A CA 000386626A CA 386626 A CA386626 A CA 386626A CA 1185024 A CA1185024 A CA 1185024A
- Authority
- CA
- Canada
- Prior art keywords
- signalling
- wire
- pair
- voltage
- central device
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M9/00—Arrangements for interconnection not involving centralised switching
- H04M9/002—Arrangements for interconnection not involving centralised switching with subscriber controlled access to a line, i.e. key telephone systems
- H04M9/003—Transmission of control signals from or to the key telephone set; signalling equipment at key telephone set, e.g. keyboard or display equipment
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
- H04L25/40—Transmitting circuits; Receiving circuits
- H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
- H04L25/4906—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using binary codes
Abstract
ABSTRACT OF THE INVENTION
"SIGNALLING IN PBX SYSTEMS"
The exchange ZSt is star-connected to the telephones TSl to TSx via four-wire subscriber lines each comprising a signalling wire-Pair c, d used for two-way alternate digital data transmission. This data transmission is by line voltage variation in one direction (ZSt to TS)and by line current variation in the other direction. To inhibit noise on the speech wire-pair a, b a sending unit Sz has a reactive circuit R1, Cl, R2, R3, C2 to deform rectangular pulses whose harmonics are normally bad from the point of view of noise.
Since this deformantion tends to introduce phase shifts, a receiving circuit Ez corresponding to the one Et used at the receiving end (TS) detects the transmitted pulses and provides synchronising signals for a control unit Pz which synchronises an oscillator Oszl with the receiving end oscillator Osz2.
(Fig. 1)
"SIGNALLING IN PBX SYSTEMS"
The exchange ZSt is star-connected to the telephones TSl to TSx via four-wire subscriber lines each comprising a signalling wire-Pair c, d used for two-way alternate digital data transmission. This data transmission is by line voltage variation in one direction (ZSt to TS)and by line current variation in the other direction. To inhibit noise on the speech wire-pair a, b a sending unit Sz has a reactive circuit R1, Cl, R2, R3, C2 to deform rectangular pulses whose harmonics are normally bad from the point of view of noise.
Since this deformantion tends to introduce phase shifts, a receiving circuit Ez corresponding to the one Et used at the receiving end (TS) detects the transmitted pulses and provides synchronising signals for a control unit Pz which synchronises an oscillator Oszl with the receiving end oscillator Osz2.
(Fig. 1)
Description
502~L
Signalling in PBX systems This invention concerns si~nalling in PBX systems where a plurality of telephone sets are connected to a central device in a radial configuration (star-arrangement). In small private branch exchanges (PBXs) ~here two-way alternate signalling ta~es place between the individual telephone sets and a central control device common to themr this signalling takes place via a signalling wire-pair which, together with the speech wire-pair, forms the four-wire subscriber line. The telephone sets receive mainly connection data for visual display elements fitted to them; the display elements may for example be in the form of LED's and/or a display-indicator. By means of the display-indicator, a particular subscriber can for example be informed about the call number selected or about accumulated charges. The engaged condition of the internal or the existing external circuits can be indicated by lighting up of the respective LED's.
The data for all display elements on a telephone set can be gathered together in one data block and transmitted as binary digital signals. This can be effected by digital signals whose binary values are defined by different amplitudes of the signalling line voltage. The ~-bit, for example, can correspond to the quiescent value of the signalling voltage, while the l-bit can represent an active signal in the form of a voltage reduction. Control of the assigned voltage states is by means of a sending unit, which in turn is controlled by a oontrol uhitr wihicb can for ex~mple be a processor, contained in tih~ central d~vice. The-signalling wire-pair is also used to transmit information wnich comes frcm the telephone sets and in par,icular si~s the ac,uation oi in.dividual]ieys. ~esides 5~)~4 the number selection keys, other ke~s can be provided which allow specific operating procedures or by the actuation of which it is possible to sign~l the type of connection intended. It is therefore possible to distinguish whether an internal connection to another telephone set of the private branch exchange is to be established, or an external connection to a telephone set of the public network or to a telephone set of another private automatic branch exchange.
The binary values of the data coming from the telephone sets can be characterized by different signalling line current values. In the case of two-way alternate signalling the data for each direction can be combined in a data block.
The data blocks are transmitted continually and not only when there is a change in the data which they contain. It is also possible to have hit-by-bit interleaving of the data to be assigned to both directions within a data block.
Two-way alternate signalling requires accurate timing of the sending functions. To achieve this, the clock pulse used as a basis for sending the data bits in the telephone set must coincide in time with the clock pulse which determines the sending of the data bits in the central device. Since it is a prerequisite when signalling for the voltage or the current on the signalling line to be varied, it is necessax~ to ensure that the permissible noise voltage is not exceeded by the sending pulses thereby generated. This also applies when the four-wire subscri~er lines have a very short line leng~h.
It is an object of the invention to sa~isfy the requirements o~ synchroni7ation and suppression of noise by simple means.
.
S0;24 According to this invention there is provided apparatus ror use in a small private branch exchange system in which a pluralty of telephone sets are connected in a star-arrange~ent to the central device via respective associated four-wire subscriber lines each comprising a speech wire-palr and a signalling wire-pair which latter wire-pair provides two-way alternate digital data .ransmission between the associated telephone set and the central device, the transmission in one direction being provided by variation of signalling line voltage and in the other direction by signalling line current variation, the transmission from the central device to the telephone sets employing a higher packing density than in the other direction, said apparatus comprising a sending unit for transmitting voltage pulses as said digital data via the signalling wire-pair (signalling line voltage variation), a reactive circuit arranged to deform rectangular vol~age pulses produced for transmission as said digital data and two substantially corresponding receiving circuits one of which is connected to the sending unit and arranged at the transmitting.end to provide a synchronising signal as a result of detection of each transmitted pulse, the other receiving circuit being for use at the receiving end for pulse detection and synchronisation so that timing signals at transmitting and receiving ends can be made mutually synchronous .
Due to deformation of the pulses forming the binary digits, the deformation consisting essentially in rounding of the pulse cornersr the noise voltagP occorring in the speech wires as a result of signalling is reduced in comparison with the use of rectang-llar pulses. Consequently, the per~issible n~ise voltage nee~ not be exceede~ even with ;
~s~
very short subscriber lines. For most applications with two-way alternate sign~lling, a low transmission frequencyr for example 250 Hz, is used. With such a frequency, the harmonics are in a range which is preferable for the ear.
Due to the deformation introduced and the associated attenuation of the harmonics, the transmission level can be raised without at the same time increasing the speech line noise voltaye. The result is a reduction of susceptibility to noise.
Since the pulses registered by the receiving circuits are used to provide synchronization pulses, there is no longer a phase shift between the drive signal for the sending unit and the pulse actually transmitted, which is caused during deformation by means of the reactive circuit.
Since synchronization takes place relative to a predetermined direction with each pulse to be assigned to-this direction within a data block, the required clock pulse can be derived from an oscillator which, in the simplest of designs, need not have a high degree of frequency stability.
The control of display elements at the telephone sets requires transmission with a greater packing density than in the opposite direction since active data is only ever transmitted from the telephone set when a key is actuated.
At other times, for example, 0-bits corresponding to the quiescent value of the line are sent. Preferably said deformation is carriad out for those pulses which are generated by the amplitude variation of the signalling line voltage and serve to transmit information from the central device to the telephone sets.
An embodiment of this inven~ion will now be described, by way of example, with -eference .o the accompanying drawings in which:-~ ~5029L
~ 5Figl is a block circuit di~gr~m o~ PBX ~stem e~bodyin~
this invention,~nd Fig2 is a set of graphs illustrating the operation of the system shown in Figl.
The block circuit diagram of FIG 1 shows the basic structure of a small private branch exchange in which two-way alternate signalling takes place between central device and individual telephone sets~ Only the details necessary for understanding the invention are shown.
In the small private branch exchange shown in FIG 1, the individual telephone sets TSl to TSx are connected in radial configuration (star-arrangement) to a central device ZSt via a four-wire subscriber line Ltg. Each subscriber line consists of a speech wire pair a, b and a signalling wire pair c, d. The wires a, b are used for transmitting the speech data and ringing current. The wires c, d are used for two-way alternate signalling between the individual telephone sets and the central device, while at the same ti~e supplying the necessary supply voltage to those units of each telephone set which are associated with the signalling and which are shown combined for telephone set TSl in a digital transmission unit BS. This supply voltage is fed by current transformer supplied by the mains voltage, which in the same way can also deliver the supply voltage to be connected to the speech wires ~or supplying the microphone. This is indicated by the circuit symbol signifying a multiple correction at one output of the unit SE.
The speech circuit SS is connected to the speech wires a, b leading ~o each telephone set; the speech circuit SS, apart from processing the speech data in connection with the ~502~
- 6 ~
handset H~, c~ntains a terminating cixcult. Internal connections can be estahlished between the individual telephone sets and the possibility exists of connection to an external line EL, which can be a line to the public telephone network or to another private branch exchange.
For example, for a total of 16 telephone sets which together with the central device form the small private branch exchange, four external lines can be provided. The type of connection desired can, for example, be signalled by the actuation of the pushbutton keys provided for the purpose on each telephone set. For telephone set TSl the possibility of initiating the transmission of certain data by operating keys is indicated by the key pad TB. The key Tw is intended to symbolize the keys of a conventional number selection keyboard, while the key Te represents a series of keys by means of which specific additional operating proce-dures can be initiated. If, for example, depression of a key intended ror the purpose - which may be one of the keys Te - gives a signal of the intention to set up an external connection, then subsequent operation of the number selection keys results in output of the assigned selection data. In systems with normal dial pulse generation by loop interruptibn, this, controJ,led by the control unit Pz in the central device, can be effected by the unit IW. ~he unit MF provides the possibility of delivering the necessary selection data in a known manner in a multiple-frequency co~e. The control unit Pz also supplies the connectinq commands for the switching matrix network KN, by means of which the connection can be switched through by appropriate actuation of its crosspoints. If an internal connection to another telephone set of the private branch exchange is desiredr the control unit issues appropriate connecting commands for the switching matrix network.
~502~
-- 7 ~
sefore being processed, the data transmitted from a telephone set can be b~lffer-stored by the control unit Pz in a me~ry which is not specifically illustrated. Transmission of this data can take place by means of binary digital signals, whose binary values are characterized by a predefined quiescent current value or by a drop in the signalling ~ine current. This current drop can be brought about in every telephone set by the sending device ~, which in turn is controlled by a control unit Pt which first receives and processes the stimuli coming from the keys. This control unit is also used to register the lifting of the handset and to pass information to this effect to the central device.
The sending device S can consist essentially of an electronic switch by means of whIch a first o~ two current regulator units, namely current regulator unit IRl wh~ch serves to supply the control unit Pt, is switched to an inactive state.
During this time, the powex supply to this control unit is maintained by means of a storage element contained in the regulator unit.
In the unit BS of each telephone set there is a second regulator circult IR2 through which visual display elements, referenced by the display element L, are supplied with power.
These display elements can be light emitting diodes by means o~ which, for example, the engaged condition of the respecti~e Pxternal lines or the engaged condition of the internal lines is indicated. These L~D's can be connected in series in order to reduce their current consumption.
Those LED's which are to be switched off can each be e~fectively bypassed by means of an electronic switch.
These swit~hes are con~rolled by the control unit Pt, which for its part receives appropxiate connection information fxol;l tne central device via receiving circuit Et.
A constant current is consumed by the regulator circuit IR2. The current flowing via the c, d wires of the signalling line therefore has a value which essentially corresponds to the sum of the current drawn by both regulator uni~s. Addea to this current value is the current consumed by the sending device S and by the receiving circuit Et, which in comparison is negligibly low. If, for example, the regulator unit IRl is switched off by the sending device, then the current flowing in the signalling wire-pair is reduced by the value of the current otherwise consumed by this regulator. Consequently, a modulation of the current flowing on the signalling line takes place.
The binary values of the digital data to be transmitted are therefore formed by the current drop, which can correspond to a l-bit, and, for example, by the quiescent current value of the signalling line, which then corresponds to the O-bit.
This data coming from the te]ephone set can be gathered separately in a data block, data blocks then being transmitted alternately to the central device and from the central device to the telephone set. The data to be transmitted from a telephone set can also be interleaved with the data transmitted from the central ~evice bit-by-bit within a data block which is to be formed.
Tne digital data transmitted from the telephone sets is registered by a receiving circuit El to Ex coupled to one wire of each signalling wire-pair and passed to the control unit Pz in the ceniral device. There is therefore a separate receivlng circuit for each teleph~ne. ~his receiving S~2'~
~ g circuit can consist essentially of a resistor inserted in the d-wire and a transistor or operational amplifier to evaluate the voltage drop across this resistor. On the basis of the data received, the control Ullit intiates the functions which are to follow.
~he data transmitted from the central device ZSt to the individual telephone sets, mainly involving connection information for visual display elements, are transmitted as binary digital signals via the relevant signalling wire-pair.
The binary values of the entire information for a telephone set which is to be gathered in a data block are formed by a quiescent voltage value and by a voltage drop.
In many cases the same data has to be transmitted to the individual telephone sets. This can be achieved by means of a common sending circuit Sz control~ed by the control unit Pz, whereby the sending circuit is multiple-connected at the output end with one wire o~ each of the signalling wire-pairs. In the practical example the sending circuit is coupled to each c-wire. The sendin~ circuit Sz conta~ns a voltage regulator SR, via which a predetermined 7 DC voltage supplied by the unit SE is applied to the signalling wire-p~ir. This serves as the supply voltage for the units coupled to this line in the respective telephone sets.
The active binary value corresponding for example to a l-bit is intended, as already mentioned, to be formed by a determinate drop in the voltage on the signalling wire-pair-The bit pattern corresponding to the information to be transmitted in a data block is transmitted by a corresponding .
~5~
~- 10 --trans~itter bit timer to the sending circuit Sz by the control unit P~. The transmitter bit timing is applied via the base resistor R5 to the base of the transistor T2 providecl as a level converter. At each active transmitter bit timing pulse for a bit pattern shown, for example, in graph a of FIG2, the transistor T2 is driven. ~s a result, driving potential is applied to the base of the transistor Tl via the load resistor R4 and the resistors R2 and R3. ~y turning this transistor on, the Zener diode ZDl is bypassed Consequently, the potential at the so-called earth connection of the integrated regulator circuit SR is reduced by the value of the Zener voltage. The output voltage of the regulator circuit follows this drop. At each transmitter bit timing pulse which is applied within the framework Of the bit pattern predefined by the control unit, the voltage across the signalling wire-pair drops by a determinate value, for example 3 V. Since individual telephone sets can be coupled directly or via only very short subscriber lines to the central device, it h~s to be ensured that no inadmissibly high noise voltage occurs on the speech line when the pulses are transmitted. Since a low transmission frequency of for example 250 Hz can be used for signalling, the harmonics in the case of rectangular pulse generation lie in a range in which the ear is very sensitive. In the sending circuit there are RC logic elements by means of which a deformation of the transmitted pulses is achieved.
This consists essentially in a rounding of the corners of the pulses to be transmitted. This is achieved by means of time circuits formed from the resistor Rl and capacitor Cl and from the resistors R2, R3 and capacitor C2. The capacitor C3 connectea across the voltage regulator serves to suppress the oscillation tendency of the regulator. If ~ ~s~
the individual telephone sets are intended to xeceive different data, this can be effected by means of a simple selection circuit Sl tc Sx, provided accordingly for each telephone set. By means of this additional sending circuit it is them possible to insert an additional data bit in a position, predetermined for each respective telephone set, in the data block transmitted by the common sending circuit Sz. This can be effected by means of--a voltage drop on the d-wire which leads to the ~elephone set which is to xeceive the information. ~s a result, the entire relevant information in the data block in question is ~valuated only by the receiving circuit contained in this assigned telephone set, while being ignored by the control units of the other ,elephone sets which evaluate pulses received. The selection circuit which in each case is coupled to a d-wire can, as shown for the circuit Sl, be in the form of a ~ener diode ZD2 inserted in this ~re; this Zener diode can be bypassed by means of transistor T3 which i5 driven by the control unit via resistor R6. If this transistor is turned on by a drive pulse supplied by the control unit, then the voltage across the signalling wire-pair is reduced by the value of the Zener voltage. In this way~ therefore, it is possible to insert a l-bit in the data block for a specific telephone set, while for all other telephone se~s there is a O-bit in this position. These latter telephone sets are so arran~ed that this received data block is not evaluated~
If it is intended for all the telephone sets to evaluate information, then the common sending circuit Sz in the central de~ice can transmit the appropriate selection bit in the daia block at the same time. Selection of a specific telephone set by inserting a selection bit defined by a voltage drop is possible, since in the telephone 5~
- 12 ~
set no reference potential is fixed ~or the wires of the signalling wire pair, In the telephone set, the receiving circuit Et inserted in the signalling line evaluates the voltage variations occurring on the wires of the relevant signalling wire-pair-In this way it is possible to determine the data bits defined by voltage drops. The receiver of the incoming data bits is very simply in the form of the transistor T6, whose emitter is connected to the c-wire while its base is connected via the base resistor Rl~ to the plus side of the capacitor C5 connected to the d-wire. ~lth t~ansistor T7 turned on, this capacitor C5 is charged via Zener diodes ZD3 to a voltage which is lower than the voltage on the c-wire by the value of the Zener voltage. If the sending circuit in the central device causes a voltage drop, then the voltage drops for example by 3 V, while the voltage across the capacitor CS
keeps the base potential of the transistor T6 roughly constant. If the Zener voltage of the Zener diode ZD3 is chosen such that together with the base emitter voltage of the transistor T6 it is less than or at most equal to the voltage drop which ha~ taken place, then the transistor is blocked. At the end of each voltage drop, the transistor rr6 becomes conductive again. Each voltage drop is therefore transmitted to the control unit P_ as an appropriate control pulse. Eor this purpose, the voltage drop occurring at collector resistor R15 is used. The collector circuit also contains a delay circuit consisting of th~ resistor R16 and the capacitor C6. This delay circuit serves the purpose of stopping momentary drops in the signal voltage due to noise from belng evaluated.
As already explained, there is a deformation of the active ~ ~S~)~4 signals, for~ed b~ volta~e drops, which are transmitted by the sending unit Sz of the central device ZS_. This is ef~ected by means of xeactive components and serves, especially with regard to short subscriber lines, to reduce the noise voltage on the speech lines. In the practical example, the corners of each pulse transmitted are rounded b~ RC networ~s formed from the resistor Rl and capacitor Cl, and from the resistors R2 and R3 and capacitor C2. ~s a result of these RC networks, a phase shift occurs between the transmitter bit timing pulse which is supplied by the control unit Pz and the signal ~ransmitted due to this timing pulse. Two-way alternate signalling, in which the data is either sent one block from the central device to the relevant telephone set and then one block in the opposite direction, or in which the data bits to be assigned alternately to the two directions are interleaved bit-by-bit within a da~a block, requires accurate synchxonization of the t~mes of transmission in the circuits described. The clock pulse used as a basis for transmitting the data bits in the telephone ~et must agree with the clock pulse which aetermines the transmission of the data bits in the central device. For this purpose, mutual synchronization of those units from which the clock pulse is derived is necessary.
In the practical example, the clock rates required for the control unit Pz of the central device 7st are derived from the oscillator arrangement Oszl. For the control unit Pt of the telephone set TSl, the necessary clock rates are derived ~rom the oscillator arrangement Osz2 with divider circuits, which are not illustrated further, interposed.
The same applies to the other telephone sets TS.
The endeavour is to construct the individual units of small private branch exchanges in a cost-effective manner.
~850~
~ 14 -Consequentl~ simple oscillator circuits are used for which thexe`are no exacting demands with regard to their frequency stability. However, in order to adhere to the required clock accuracy~ it is necessary for them also to be synchronized within each data block transmitted, these synchronization pulses being derived from the pulses trans-mitted in a given direction. The transmitter bit timing and the pulse received in the individual telephone sets as a result of this transmitter bit timing cannot be used for this synchronization, because the phase shift mentioned above occurs on account of the RC networks provided for the purpose of deforming the send pulses. In order ~o eliminate this phase shift, the same simple receiving circuit as used in the individual telephone sets is coupled to the send line of the central device. In this way it is possible to effect the necessary timing in the central device for the arrival of signal pulses which are transmitted from a telephone set ~ue to the two identical receiving circuits,a predetermined edge o~ the transmitted pulse, lor exam~le the descending pulse edge, is recognized simultaneously by them.
Consequently, synchronization between the oscillator arrangement in the central device and the oscillator arrangements in the individual telephone sets can be re-established by recognition of this pulse edge, which then in each case results in a synchronization pulse. It is there~ore possible to repeat synchronization frequently within each data block, so that cheap oscillator circuits with a greater tolerance can be employed.
The receiving circuit Ez additionally connected to the send line in the central device/ in the same way as the receiving circuit Et which is provided in each telephone set, contains a Zener diode, namely the Zener diode ZD4, for voltage ~85~2~
evaluation. A certain Zener current is maintained for this Zener diode ~ means of a high-value resistor R7. Transistor T4 coupled to the Zener diode on its emitter side and via base resistor R8 is controlled by the voltage drop of the Zener diode. This transistor T4 corresponds in terms of its function to the transistor T6 in the receiving circuit Et.
A collector resistor of the transistor T4 is designated R9.
The voltage drop occurring across this resistor, which in each case de~ines a transmitted pulse, controls the transistor T5 via resistor R10. The resistor R10 in conjunc~ion with capacitor C~, forms a delav circuit which serves the purpose of preventing pulse spikes from ta~ing place.
The transistor T5 serves solely as a level converter. The voltage drop occurring at its collector resistor ~11 is supplied as a synchronizing signal to the control unit Pz via the resistor R12. This control unit can then reco~nize for example each descending edge of a transmitted pulse.
The same edge is recogni7ed with negligible delay times simultaneously by the control unit Pt on account of the received pulse transmitted to it in the same way. Each control unit then derives from ~his a synchronization pulse ~or the oscillator circuits Oszl and Osz2 respectively.
The receiving unit Ez, unlike the receiving unit E , does not contain those components provided in unit Et for specific matching to the line conditions. In the case of the receiving circuit Ez, which is arranged at the beginning of the line relative to the sending direction, the influence o~ the transmission line can be aisregarded.
The pulse aiagram in graph a of FIG 2 shows an example of a bit pattern for a data block to be transmitted from the central device. Each bit pattern shown corresponds to the transmitter bit timing applied by the control unit Pz to the 50~
. 16 com~on sending circuit ~z. The data block, which is trans~
mitted continually and not only when there are changes of information, can begin with a synchronization bit S~ which can have twice the n~rmal bit duration in order to distinguish it from the other data bits. The following data bit Se drawn in a broken line can be the selection bit which has been described and which is inserted into the data block by one of the selection circuits Sl to Sx in order to select a specific telephone set. In the example, the bit sequence "O,lrO,l" follows on. The position of these bits in the data block determines the selection address for individual visual display elements. This bit sequence determines the state of ill~nination of the display elements. The transmission of a l-bit, for example, will indicate that the assigned display element is to be switched to the active state. If the element is an LED, then it is thereby put in to its illuminated state. Thi-s is ensured by appropriate drive signals from the contro~ unit of the telephone set concerned.
,, An acknowledgment bit Q and a parity bit P can ~ollow. In the pæactical example illustrated in graph a F~G 2, an interval of the same length in each case is inserted betwee~
the data bits. During this interval, a data bit sent from the telephone can be inserted as a O-bit or a l-bit during bit-by-bit ~nterleaving.
Graph b in FIG 2 shows the potential profile on the signalling wire-pair res~-lting from the transmitter bit timing predeter~ined by the control unit as per graph _. As already explained, each clock pulse leads to a drop in the signal voltage. This drop from the signal voltage quiescent value Ur to the value Us thereby defines each l-bit. A phase :
:`
~1 ~&5(~4 shift t_ exists between each transmitter bit timing pulse and the pulse actually transmitted. This phase shift is produced by the RC networks which are connected into the sending circuit in order to deform the transmitted pulses before t~ansmission from the sending end. Consequently, the necessary reduction of noise voltage is also achieved in those cases where a telephone set is connected to the central device via a very shori subcriber's line. The transmitted pulse is received during its pulse time tz both in the receiving circuit at the sending end Ez and in the receiving circuit Et and fed to the relevant control unit Pz or Pt.
Each descending edge can be used for synchronization of the existing oscillator circuits. This is indicated in each case by the reference Sl in graph b. During the time Ts, a data bit can be sent from the relevant telephone set to the central device.
Signalling in PBX systems This invention concerns si~nalling in PBX systems where a plurality of telephone sets are connected to a central device in a radial configuration (star-arrangement). In small private branch exchanges (PBXs) ~here two-way alternate signalling ta~es place between the individual telephone sets and a central control device common to themr this signalling takes place via a signalling wire-pair which, together with the speech wire-pair, forms the four-wire subscriber line. The telephone sets receive mainly connection data for visual display elements fitted to them; the display elements may for example be in the form of LED's and/or a display-indicator. By means of the display-indicator, a particular subscriber can for example be informed about the call number selected or about accumulated charges. The engaged condition of the internal or the existing external circuits can be indicated by lighting up of the respective LED's.
The data for all display elements on a telephone set can be gathered together in one data block and transmitted as binary digital signals. This can be effected by digital signals whose binary values are defined by different amplitudes of the signalling line voltage. The ~-bit, for example, can correspond to the quiescent value of the signalling voltage, while the l-bit can represent an active signal in the form of a voltage reduction. Control of the assigned voltage states is by means of a sending unit, which in turn is controlled by a oontrol uhitr wihicb can for ex~mple be a processor, contained in tih~ central d~vice. The-signalling wire-pair is also used to transmit information wnich comes frcm the telephone sets and in par,icular si~s the ac,uation oi in.dividual]ieys. ~esides 5~)~4 the number selection keys, other ke~s can be provided which allow specific operating procedures or by the actuation of which it is possible to sign~l the type of connection intended. It is therefore possible to distinguish whether an internal connection to another telephone set of the private branch exchange is to be established, or an external connection to a telephone set of the public network or to a telephone set of another private automatic branch exchange.
The binary values of the data coming from the telephone sets can be characterized by different signalling line current values. In the case of two-way alternate signalling the data for each direction can be combined in a data block.
The data blocks are transmitted continually and not only when there is a change in the data which they contain. It is also possible to have hit-by-bit interleaving of the data to be assigned to both directions within a data block.
Two-way alternate signalling requires accurate timing of the sending functions. To achieve this, the clock pulse used as a basis for sending the data bits in the telephone set must coincide in time with the clock pulse which determines the sending of the data bits in the central device. Since it is a prerequisite when signalling for the voltage or the current on the signalling line to be varied, it is necessax~ to ensure that the permissible noise voltage is not exceeded by the sending pulses thereby generated. This also applies when the four-wire subscri~er lines have a very short line leng~h.
It is an object of the invention to sa~isfy the requirements o~ synchroni7ation and suppression of noise by simple means.
.
S0;24 According to this invention there is provided apparatus ror use in a small private branch exchange system in which a pluralty of telephone sets are connected in a star-arrange~ent to the central device via respective associated four-wire subscriber lines each comprising a speech wire-palr and a signalling wire-pair which latter wire-pair provides two-way alternate digital data .ransmission between the associated telephone set and the central device, the transmission in one direction being provided by variation of signalling line voltage and in the other direction by signalling line current variation, the transmission from the central device to the telephone sets employing a higher packing density than in the other direction, said apparatus comprising a sending unit for transmitting voltage pulses as said digital data via the signalling wire-pair (signalling line voltage variation), a reactive circuit arranged to deform rectangular vol~age pulses produced for transmission as said digital data and two substantially corresponding receiving circuits one of which is connected to the sending unit and arranged at the transmitting.end to provide a synchronising signal as a result of detection of each transmitted pulse, the other receiving circuit being for use at the receiving end for pulse detection and synchronisation so that timing signals at transmitting and receiving ends can be made mutually synchronous .
Due to deformation of the pulses forming the binary digits, the deformation consisting essentially in rounding of the pulse cornersr the noise voltagP occorring in the speech wires as a result of signalling is reduced in comparison with the use of rectang-llar pulses. Consequently, the per~issible n~ise voltage nee~ not be exceede~ even with ;
~s~
very short subscriber lines. For most applications with two-way alternate sign~lling, a low transmission frequencyr for example 250 Hz, is used. With such a frequency, the harmonics are in a range which is preferable for the ear.
Due to the deformation introduced and the associated attenuation of the harmonics, the transmission level can be raised without at the same time increasing the speech line noise voltaye. The result is a reduction of susceptibility to noise.
Since the pulses registered by the receiving circuits are used to provide synchronization pulses, there is no longer a phase shift between the drive signal for the sending unit and the pulse actually transmitted, which is caused during deformation by means of the reactive circuit.
Since synchronization takes place relative to a predetermined direction with each pulse to be assigned to-this direction within a data block, the required clock pulse can be derived from an oscillator which, in the simplest of designs, need not have a high degree of frequency stability.
The control of display elements at the telephone sets requires transmission with a greater packing density than in the opposite direction since active data is only ever transmitted from the telephone set when a key is actuated.
At other times, for example, 0-bits corresponding to the quiescent value of the line are sent. Preferably said deformation is carriad out for those pulses which are generated by the amplitude variation of the signalling line voltage and serve to transmit information from the central device to the telephone sets.
An embodiment of this inven~ion will now be described, by way of example, with -eference .o the accompanying drawings in which:-~ ~5029L
~ 5Figl is a block circuit di~gr~m o~ PBX ~stem e~bodyin~
this invention,~nd Fig2 is a set of graphs illustrating the operation of the system shown in Figl.
The block circuit diagram of FIG 1 shows the basic structure of a small private branch exchange in which two-way alternate signalling takes place between central device and individual telephone sets~ Only the details necessary for understanding the invention are shown.
In the small private branch exchange shown in FIG 1, the individual telephone sets TSl to TSx are connected in radial configuration (star-arrangement) to a central device ZSt via a four-wire subscriber line Ltg. Each subscriber line consists of a speech wire pair a, b and a signalling wire pair c, d. The wires a, b are used for transmitting the speech data and ringing current. The wires c, d are used for two-way alternate signalling between the individual telephone sets and the central device, while at the same ti~e supplying the necessary supply voltage to those units of each telephone set which are associated with the signalling and which are shown combined for telephone set TSl in a digital transmission unit BS. This supply voltage is fed by current transformer supplied by the mains voltage, which in the same way can also deliver the supply voltage to be connected to the speech wires ~or supplying the microphone. This is indicated by the circuit symbol signifying a multiple correction at one output of the unit SE.
The speech circuit SS is connected to the speech wires a, b leading ~o each telephone set; the speech circuit SS, apart from processing the speech data in connection with the ~502~
- 6 ~
handset H~, c~ntains a terminating cixcult. Internal connections can be estahlished between the individual telephone sets and the possibility exists of connection to an external line EL, which can be a line to the public telephone network or to another private branch exchange.
For example, for a total of 16 telephone sets which together with the central device form the small private branch exchange, four external lines can be provided. The type of connection desired can, for example, be signalled by the actuation of the pushbutton keys provided for the purpose on each telephone set. For telephone set TSl the possibility of initiating the transmission of certain data by operating keys is indicated by the key pad TB. The key Tw is intended to symbolize the keys of a conventional number selection keyboard, while the key Te represents a series of keys by means of which specific additional operating proce-dures can be initiated. If, for example, depression of a key intended ror the purpose - which may be one of the keys Te - gives a signal of the intention to set up an external connection, then subsequent operation of the number selection keys results in output of the assigned selection data. In systems with normal dial pulse generation by loop interruptibn, this, controJ,led by the control unit Pz in the central device, can be effected by the unit IW. ~he unit MF provides the possibility of delivering the necessary selection data in a known manner in a multiple-frequency co~e. The control unit Pz also supplies the connectinq commands for the switching matrix network KN, by means of which the connection can be switched through by appropriate actuation of its crosspoints. If an internal connection to another telephone set of the private branch exchange is desiredr the control unit issues appropriate connecting commands for the switching matrix network.
~502~
-- 7 ~
sefore being processed, the data transmitted from a telephone set can be b~lffer-stored by the control unit Pz in a me~ry which is not specifically illustrated. Transmission of this data can take place by means of binary digital signals, whose binary values are characterized by a predefined quiescent current value or by a drop in the signalling ~ine current. This current drop can be brought about in every telephone set by the sending device ~, which in turn is controlled by a control unit Pt which first receives and processes the stimuli coming from the keys. This control unit is also used to register the lifting of the handset and to pass information to this effect to the central device.
The sending device S can consist essentially of an electronic switch by means of whIch a first o~ two current regulator units, namely current regulator unit IRl wh~ch serves to supply the control unit Pt, is switched to an inactive state.
During this time, the powex supply to this control unit is maintained by means of a storage element contained in the regulator unit.
In the unit BS of each telephone set there is a second regulator circult IR2 through which visual display elements, referenced by the display element L, are supplied with power.
These display elements can be light emitting diodes by means o~ which, for example, the engaged condition of the respecti~e Pxternal lines or the engaged condition of the internal lines is indicated. These L~D's can be connected in series in order to reduce their current consumption.
Those LED's which are to be switched off can each be e~fectively bypassed by means of an electronic switch.
These swit~hes are con~rolled by the control unit Pt, which for its part receives appropxiate connection information fxol;l tne central device via receiving circuit Et.
A constant current is consumed by the regulator circuit IR2. The current flowing via the c, d wires of the signalling line therefore has a value which essentially corresponds to the sum of the current drawn by both regulator uni~s. Addea to this current value is the current consumed by the sending device S and by the receiving circuit Et, which in comparison is negligibly low. If, for example, the regulator unit IRl is switched off by the sending device, then the current flowing in the signalling wire-pair is reduced by the value of the current otherwise consumed by this regulator. Consequently, a modulation of the current flowing on the signalling line takes place.
The binary values of the digital data to be transmitted are therefore formed by the current drop, which can correspond to a l-bit, and, for example, by the quiescent current value of the signalling line, which then corresponds to the O-bit.
This data coming from the te]ephone set can be gathered separately in a data block, data blocks then being transmitted alternately to the central device and from the central device to the telephone set. The data to be transmitted from a telephone set can also be interleaved with the data transmitted from the central ~evice bit-by-bit within a data block which is to be formed.
Tne digital data transmitted from the telephone sets is registered by a receiving circuit El to Ex coupled to one wire of each signalling wire-pair and passed to the control unit Pz in the ceniral device. There is therefore a separate receivlng circuit for each teleph~ne. ~his receiving S~2'~
~ g circuit can consist essentially of a resistor inserted in the d-wire and a transistor or operational amplifier to evaluate the voltage drop across this resistor. On the basis of the data received, the control Ullit intiates the functions which are to follow.
~he data transmitted from the central device ZSt to the individual telephone sets, mainly involving connection information for visual display elements, are transmitted as binary digital signals via the relevant signalling wire-pair.
The binary values of the entire information for a telephone set which is to be gathered in a data block are formed by a quiescent voltage value and by a voltage drop.
In many cases the same data has to be transmitted to the individual telephone sets. This can be achieved by means of a common sending circuit Sz control~ed by the control unit Pz, whereby the sending circuit is multiple-connected at the output end with one wire o~ each of the signalling wire-pairs. In the practical example the sending circuit is coupled to each c-wire. The sendin~ circuit Sz conta~ns a voltage regulator SR, via which a predetermined 7 DC voltage supplied by the unit SE is applied to the signalling wire-p~ir. This serves as the supply voltage for the units coupled to this line in the respective telephone sets.
The active binary value corresponding for example to a l-bit is intended, as already mentioned, to be formed by a determinate drop in the voltage on the signalling wire-pair-The bit pattern corresponding to the information to be transmitted in a data block is transmitted by a corresponding .
~5~
~- 10 --trans~itter bit timer to the sending circuit Sz by the control unit P~. The transmitter bit timing is applied via the base resistor R5 to the base of the transistor T2 providecl as a level converter. At each active transmitter bit timing pulse for a bit pattern shown, for example, in graph a of FIG2, the transistor T2 is driven. ~s a result, driving potential is applied to the base of the transistor Tl via the load resistor R4 and the resistors R2 and R3. ~y turning this transistor on, the Zener diode ZDl is bypassed Consequently, the potential at the so-called earth connection of the integrated regulator circuit SR is reduced by the value of the Zener voltage. The output voltage of the regulator circuit follows this drop. At each transmitter bit timing pulse which is applied within the framework Of the bit pattern predefined by the control unit, the voltage across the signalling wire-pair drops by a determinate value, for example 3 V. Since individual telephone sets can be coupled directly or via only very short subscriber lines to the central device, it h~s to be ensured that no inadmissibly high noise voltage occurs on the speech line when the pulses are transmitted. Since a low transmission frequency of for example 250 Hz can be used for signalling, the harmonics in the case of rectangular pulse generation lie in a range in which the ear is very sensitive. In the sending circuit there are RC logic elements by means of which a deformation of the transmitted pulses is achieved.
This consists essentially in a rounding of the corners of the pulses to be transmitted. This is achieved by means of time circuits formed from the resistor Rl and capacitor Cl and from the resistors R2, R3 and capacitor C2. The capacitor C3 connectea across the voltage regulator serves to suppress the oscillation tendency of the regulator. If ~ ~s~
the individual telephone sets are intended to xeceive different data, this can be effected by means of a simple selection circuit Sl tc Sx, provided accordingly for each telephone set. By means of this additional sending circuit it is them possible to insert an additional data bit in a position, predetermined for each respective telephone set, in the data block transmitted by the common sending circuit Sz. This can be effected by means of--a voltage drop on the d-wire which leads to the ~elephone set which is to xeceive the information. ~s a result, the entire relevant information in the data block in question is ~valuated only by the receiving circuit contained in this assigned telephone set, while being ignored by the control units of the other ,elephone sets which evaluate pulses received. The selection circuit which in each case is coupled to a d-wire can, as shown for the circuit Sl, be in the form of a ~ener diode ZD2 inserted in this ~re; this Zener diode can be bypassed by means of transistor T3 which i5 driven by the control unit via resistor R6. If this transistor is turned on by a drive pulse supplied by the control unit, then the voltage across the signalling wire-pair is reduced by the value of the Zener voltage. In this way~ therefore, it is possible to insert a l-bit in the data block for a specific telephone set, while for all other telephone se~s there is a O-bit in this position. These latter telephone sets are so arran~ed that this received data block is not evaluated~
If it is intended for all the telephone sets to evaluate information, then the common sending circuit Sz in the central de~ice can transmit the appropriate selection bit in the daia block at the same time. Selection of a specific telephone set by inserting a selection bit defined by a voltage drop is possible, since in the telephone 5~
- 12 ~
set no reference potential is fixed ~or the wires of the signalling wire pair, In the telephone set, the receiving circuit Et inserted in the signalling line evaluates the voltage variations occurring on the wires of the relevant signalling wire-pair-In this way it is possible to determine the data bits defined by voltage drops. The receiver of the incoming data bits is very simply in the form of the transistor T6, whose emitter is connected to the c-wire while its base is connected via the base resistor Rl~ to the plus side of the capacitor C5 connected to the d-wire. ~lth t~ansistor T7 turned on, this capacitor C5 is charged via Zener diodes ZD3 to a voltage which is lower than the voltage on the c-wire by the value of the Zener voltage. If the sending circuit in the central device causes a voltage drop, then the voltage drops for example by 3 V, while the voltage across the capacitor CS
keeps the base potential of the transistor T6 roughly constant. If the Zener voltage of the Zener diode ZD3 is chosen such that together with the base emitter voltage of the transistor T6 it is less than or at most equal to the voltage drop which ha~ taken place, then the transistor is blocked. At the end of each voltage drop, the transistor rr6 becomes conductive again. Each voltage drop is therefore transmitted to the control unit P_ as an appropriate control pulse. Eor this purpose, the voltage drop occurring at collector resistor R15 is used. The collector circuit also contains a delay circuit consisting of th~ resistor R16 and the capacitor C6. This delay circuit serves the purpose of stopping momentary drops in the signal voltage due to noise from belng evaluated.
As already explained, there is a deformation of the active ~ ~S~)~4 signals, for~ed b~ volta~e drops, which are transmitted by the sending unit Sz of the central device ZS_. This is ef~ected by means of xeactive components and serves, especially with regard to short subscriber lines, to reduce the noise voltage on the speech lines. In the practical example, the corners of each pulse transmitted are rounded b~ RC networ~s formed from the resistor Rl and capacitor Cl, and from the resistors R2 and R3 and capacitor C2. ~s a result of these RC networks, a phase shift occurs between the transmitter bit timing pulse which is supplied by the control unit Pz and the signal ~ransmitted due to this timing pulse. Two-way alternate signalling, in which the data is either sent one block from the central device to the relevant telephone set and then one block in the opposite direction, or in which the data bits to be assigned alternately to the two directions are interleaved bit-by-bit within a da~a block, requires accurate synchxonization of the t~mes of transmission in the circuits described. The clock pulse used as a basis for transmitting the data bits in the telephone ~et must agree with the clock pulse which aetermines the transmission of the data bits in the central device. For this purpose, mutual synchronization of those units from which the clock pulse is derived is necessary.
In the practical example, the clock rates required for the control unit Pz of the central device 7st are derived from the oscillator arrangement Oszl. For the control unit Pt of the telephone set TSl, the necessary clock rates are derived ~rom the oscillator arrangement Osz2 with divider circuits, which are not illustrated further, interposed.
The same applies to the other telephone sets TS.
The endeavour is to construct the individual units of small private branch exchanges in a cost-effective manner.
~850~
~ 14 -Consequentl~ simple oscillator circuits are used for which thexe`are no exacting demands with regard to their frequency stability. However, in order to adhere to the required clock accuracy~ it is necessary for them also to be synchronized within each data block transmitted, these synchronization pulses being derived from the pulses trans-mitted in a given direction. The transmitter bit timing and the pulse received in the individual telephone sets as a result of this transmitter bit timing cannot be used for this synchronization, because the phase shift mentioned above occurs on account of the RC networks provided for the purpose of deforming the send pulses. In order ~o eliminate this phase shift, the same simple receiving circuit as used in the individual telephone sets is coupled to the send line of the central device. In this way it is possible to effect the necessary timing in the central device for the arrival of signal pulses which are transmitted from a telephone set ~ue to the two identical receiving circuits,a predetermined edge o~ the transmitted pulse, lor exam~le the descending pulse edge, is recognized simultaneously by them.
Consequently, synchronization between the oscillator arrangement in the central device and the oscillator arrangements in the individual telephone sets can be re-established by recognition of this pulse edge, which then in each case results in a synchronization pulse. It is there~ore possible to repeat synchronization frequently within each data block, so that cheap oscillator circuits with a greater tolerance can be employed.
The receiving circuit Ez additionally connected to the send line in the central device/ in the same way as the receiving circuit Et which is provided in each telephone set, contains a Zener diode, namely the Zener diode ZD4, for voltage ~85~2~
evaluation. A certain Zener current is maintained for this Zener diode ~ means of a high-value resistor R7. Transistor T4 coupled to the Zener diode on its emitter side and via base resistor R8 is controlled by the voltage drop of the Zener diode. This transistor T4 corresponds in terms of its function to the transistor T6 in the receiving circuit Et.
A collector resistor of the transistor T4 is designated R9.
The voltage drop occurring across this resistor, which in each case de~ines a transmitted pulse, controls the transistor T5 via resistor R10. The resistor R10 in conjunc~ion with capacitor C~, forms a delav circuit which serves the purpose of preventing pulse spikes from ta~ing place.
The transistor T5 serves solely as a level converter. The voltage drop occurring at its collector resistor ~11 is supplied as a synchronizing signal to the control unit Pz via the resistor R12. This control unit can then reco~nize for example each descending edge of a transmitted pulse.
The same edge is recogni7ed with negligible delay times simultaneously by the control unit Pt on account of the received pulse transmitted to it in the same way. Each control unit then derives from ~his a synchronization pulse ~or the oscillator circuits Oszl and Osz2 respectively.
The receiving unit Ez, unlike the receiving unit E , does not contain those components provided in unit Et for specific matching to the line conditions. In the case of the receiving circuit Ez, which is arranged at the beginning of the line relative to the sending direction, the influence o~ the transmission line can be aisregarded.
The pulse aiagram in graph a of FIG 2 shows an example of a bit pattern for a data block to be transmitted from the central device. Each bit pattern shown corresponds to the transmitter bit timing applied by the control unit Pz to the 50~
. 16 com~on sending circuit ~z. The data block, which is trans~
mitted continually and not only when there are changes of information, can begin with a synchronization bit S~ which can have twice the n~rmal bit duration in order to distinguish it from the other data bits. The following data bit Se drawn in a broken line can be the selection bit which has been described and which is inserted into the data block by one of the selection circuits Sl to Sx in order to select a specific telephone set. In the example, the bit sequence "O,lrO,l" follows on. The position of these bits in the data block determines the selection address for individual visual display elements. This bit sequence determines the state of ill~nination of the display elements. The transmission of a l-bit, for example, will indicate that the assigned display element is to be switched to the active state. If the element is an LED, then it is thereby put in to its illuminated state. Thi-s is ensured by appropriate drive signals from the contro~ unit of the telephone set concerned.
,, An acknowledgment bit Q and a parity bit P can ~ollow. In the pæactical example illustrated in graph a F~G 2, an interval of the same length in each case is inserted betwee~
the data bits. During this interval, a data bit sent from the telephone can be inserted as a O-bit or a l-bit during bit-by-bit ~nterleaving.
Graph b in FIG 2 shows the potential profile on the signalling wire-pair res~-lting from the transmitter bit timing predeter~ined by the control unit as per graph _. As already explained, each clock pulse leads to a drop in the signal voltage. This drop from the signal voltage quiescent value Ur to the value Us thereby defines each l-bit. A phase :
:`
~1 ~&5(~4 shift t_ exists between each transmitter bit timing pulse and the pulse actually transmitted. This phase shift is produced by the RC networks which are connected into the sending circuit in order to deform the transmitted pulses before t~ansmission from the sending end. Consequently, the necessary reduction of noise voltage is also achieved in those cases where a telephone set is connected to the central device via a very shori subcriber's line. The transmitted pulse is received during its pulse time tz both in the receiving circuit at the sending end Ez and in the receiving circuit Et and fed to the relevant control unit Pz or Pt.
Each descending edge can be used for synchronization of the existing oscillator circuits. This is indicated in each case by the reference Sl in graph b. During the time Ts, a data bit can be sent from the relevant telephone set to the central device.
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for use in a small private branch exchange system in which a plurality of telephone sets are connected in a star-arrangement to the central device via respective associated four-wire subscriber lines each comprising a speech wire-pair and a signalling wire-pair which latter wire-pair provides two-way alternate digital data transmission between the associated telephone set and the central device, the transmission in one direction being provided by varia-tion of signalling line voltage and in the other direction by signalling line current variation, the transmission from the central device to the telephone sets employing a higher packing density than in the other direction, said appar-atus comprising a sending unit for transmitting voltage pulses as said digital data via the signalling wire-pair (signalling line voltage variation), a reactive circuit arranged to deform rectangular voltage pulses produced for transmission as said digital data and two substantially corresponding receiving circuits one of which is connected to the sending unit and arranged at the transmitting end to provide a synchronising signal as a result of detection of each transmitted pulse, the other receiving circuit being for use at the receiving end for pulse detection and synchronisation so that timing signals at transmitting and rec-eiving ends can be made mutually synchronous.
2. Apparatus according to claim 1 wherein said receiving circuits are arranged to supply synchronising signals on detecting the leading edges of the transmitted pulses.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3036182A DE3036182C2 (en) | 1980-09-25 | 1980-09-25 | Method for the mutual transmission of binary digital signals between a central facility and telephone subscriber stations connected to it |
| DEP3036182.1 | 1980-09-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1185024A true CA1185024A (en) | 1985-04-02 |
Family
ID=6112832
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000386626A Expired CA1185024A (en) | 1980-09-25 | 1981-09-24 | Signalling in pbx systems |
Country Status (12)
| Country | Link |
|---|---|
| EP (1) | EP0048925B1 (en) |
| AR (1) | AR230911A1 (en) |
| AT (1) | ATE6719T1 (en) |
| AU (1) | AU543544B2 (en) |
| BR (1) | BR8106120A (en) |
| CA (1) | CA1185024A (en) |
| DE (1) | DE3036182C2 (en) |
| FI (1) | FI74567C (en) |
| GB (1) | GB2085695B (en) |
| IN (1) | IN155068B (en) |
| NO (1) | NO153589C (en) |
| TR (1) | TR21185A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3248276A1 (en) * | 1982-12-28 | 1984-06-28 | Standard Elektrik Lorenz Ag, 7000 Stuttgart | INTERFACE CIRCUIT FOR A TELECOMMUNICATION SYSTEM |
| DE4107593C1 (en) * | 1991-03-09 | 1992-05-21 | Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung Ev, 8000 Muenchen, De |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3215779A (en) * | 1961-02-24 | 1965-11-02 | Hallicrafters Co | Digital data conversion and transmission system |
| CA1018270A (en) * | 1972-05-23 | 1977-09-27 | Federico R. Laliccia | Key telephone system using time division and space division control |
| US4046972A (en) * | 1976-10-27 | 1977-09-06 | Bell Telephone Laboratories, Incorporated | Key telephone station set circuit |
-
1980
- 1980-09-25 DE DE3036182A patent/DE3036182C2/en not_active Expired
-
1981
- 1981-09-10 IN IN1017/CAL/81A patent/IN155068B/en unknown
- 1981-09-18 AR AR286801A patent/AR230911A1/en active
- 1981-09-21 NO NO813203A patent/NO153589C/en unknown
- 1981-09-21 AT AT81107505T patent/ATE6719T1/en not_active IP Right Cessation
- 1981-09-21 EP EP81107505A patent/EP0048925B1/en not_active Expired
- 1981-09-24 GB GB8128946A patent/GB2085695B/en not_active Expired
- 1981-09-24 TR TR21185A patent/TR21185A/en unknown
- 1981-09-24 AU AU75644/81A patent/AU543544B2/en not_active Ceased
- 1981-09-24 CA CA000386626A patent/CA1185024A/en not_active Expired
- 1981-09-24 BR BR8106120A patent/BR8106120A/en unknown
- 1981-09-24 FI FI812977A patent/FI74567C/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| GB2085695A (en) | 1982-04-28 |
| FI74567C (en) | 1988-02-08 |
| NO153589B (en) | 1986-01-06 |
| ATE6719T1 (en) | 1984-03-15 |
| EP0048925A1 (en) | 1982-04-07 |
| FI74567B (en) | 1987-10-30 |
| BR8106120A (en) | 1982-06-15 |
| AR230911A1 (en) | 1984-07-31 |
| IN155068B (en) | 1984-12-29 |
| AU7564481A (en) | 1982-04-01 |
| TR21185A (en) | 1983-12-06 |
| AU543544B2 (en) | 1985-04-26 |
| NO813203L (en) | 1982-03-26 |
| NO153589C (en) | 1986-04-16 |
| DE3036182A1 (en) | 1982-04-01 |
| FI812977L (en) | 1982-03-26 |
| EP0048925B1 (en) | 1984-03-14 |
| GB2085695B (en) | 1984-09-12 |
| DE3036182C2 (en) | 1983-12-01 |
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| MKEX | Expiry |