TECHNICAL FIELD

The invention relates to a method and apparatus in a telecommunication system for activating subscriber terminals in a digital subscriber connection including a line terminal assigned to the station side of the system, a network terminal assigned to the subscriber installation and one or more subscriber terminals, the line terminal being connected to a central clock pulse oscillator on the station side, and the net¬ work terminal and subscriber terminals containing Local clock pulse osci llators.

BACKGROUND ART

It is already known to switch over subscriber terminals from an idling state to an activated state with the aid of special activation signals in the form of DC signals.

DISCLOSURE OF INVENTION

A problem occuring in DC activation is the requirement of detecting dif¬ ferent DC Levels to enable distinguishing between idle condition cur¬ rents and activating currents. Since the idle condition current is used to maintain certain functions in the terminal during the idling state also, the level of the idle condition current is thus limited by the activation signal Level, there being Limits to how Low the former may fall and how high the latter may rise. This results in a small margin between the different voltage levels and thereby increases sensitivity to interference. Furthermore, in possible standardization one will be tied to a technique which is not optimized for the future.

The method and apparatus in accordance with the invention are charac¬ terized by the claims, and solve the problem by the activation being carried out digitally in loops with the aid of binary code words.

The system comprises, as mentioned, of a Line terminal LT on the sta¬ tion side of a connection, a network terminal NT assigned to the sub¬ scriber installation and one or more subscriber terminals ST.

Activation can be performed in synchronous or asynchrσnous/pLesiochro- nous operation, and may be initiated either from the subscriber side (the subscriber terminal ST) or from the station side (the Line termi¬ nal LT).

In activation started from the subscriber terminal ST, there is sent from it an activation request AR giving rise to temporary synchroni- zation of the clock in the network terminal NT with the clock from the terminal ST, and also -temporary activating the network terminal NT. The clock signal in the terminal ST is plesiochronous in relation to the clock signal in the Line terminal LT, which terminal is connected to the station clock functioning as master. In activation of the net- work terminal, the activation request is sent from it to the line ter¬ minal LT which, on received activation request via the station (EX ⁾ , sends out the activation order AO to the terminal NT in the same way as the activation was started from the line terminal LT. The activa¬ tion-synchronization signal received in the terminal NT gives rise to the final activation of the terminal, its synchronization to the clock puLse from the line terminal, and transmission, of equal signals to the subscriber terminal ST. An activation-synchronization signal received in the terminal ST from the terminal NT provides the final activation of the former and its synchronization to the clock pulse from the line terminal LT.

In starting activation from the line terminal LT no activation request is sent, but an activation order is sent, as previously mentioned, di¬ rectly to the terminals NT"and ST, since activation orders always go out from the terminal LT, which functions as master. Both activation request and order are processed on the station side at a higher Level than that of the line terminal. In detection of an activation request from the line terminal, a stafroiB EX sends an activation order via said terminal. Since the station EX is not part of the inventive sub-

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ject, it is not described here but is only mentioned for clarifying the inventive concept.

The subscriber terminals are normally powered from the network termi¬ nal NT. Certain more complex terminals,e.g. display screens, are pro- vided with their own power supply, however. In order to prevent total communication interruption for a power failure in the terminal NT, cer¬ tain very simple terminals may be remotely powered from the line ter¬ minal LT. These simple terminals or so-called Plain Ordinary Tele¬ phone Service (POTS) terminals may be given priority and be addressed by an address code included in the synchronization signal.

A further advantage with activation by normal transmission, as in the selected case, is thus that a plurality of individual terminals, e.g. POTS terminals, can be addressed, which is not possible with DC acti¬ vation. The hardware utilized for normal transmission is used with the seLected activation method; only very simple supplementation being ne¬ cessary. This makes the method both reliable and economically advan¬ tageous.

DESCRIPTION OF FIGURES

An apparatus in accordance with the invention is described in detail with the aid of an embodiment and with reference to the accompanying drawings, on which

Figure 1 is a block diagram of a system in which the apparatus in ac¬ cordance with the invention is applied,

Figure 2 is a more detailed diagram of the apparatus in a subscriber terminal and a first part of a network terminal, and Figure 3 is a diagram of the apparatus in a second portion of the net¬ work terminal and in the line terminal.

PREFERRED EMBODIMENT

As will be seen from Figure 1, the apparatus in accordance with the invention is included in a telecommunication system for the activation

of subscriber terminals in a digital subscriber connection, this sys¬ tem including a line terminal LT assigned to the station side, a net¬ work terminal NT assigned to the subscriber installation and one or more subscriber terminals ST.

A bus Line BL internally connects the subscriber terminal ST with the network terminal NT on the subscriber side. The signals are trans¬ ferred in time division multiplex (TDM) form and in the form of bursts. The information is transferred on the subscriber line SL between the network terminal NT and the Line terminal LT in the form of a serially continuous bit flow, i.e. in the normal transfer betueen the subscriber and station sides.

On activation, the terminals are changed from idling state to active state. Each of the subscriber terminals ST contains a transmitter KG1, a receiver M4 and a local cLock pulse oscillator CL1.

The network terminal NT contains double transmitters S1, KG3, receivers M1, M3, and clock pulse oscillators CL2, CL3, since it sends and re¬ ceives data bursts in TDM form,to and from the bus line, but sends and re¬ ceives series, continuous data flows to and from the subscriber line. The line terminal LT contains a receiver M2 and a transmitter S2. The terminal obtains clock pulse control from the central station clock MCL.

Depending on the position, in the activation cycle, the transmitter S1 may consist either of a code transmitter KS1 for transmitting a conti¬ nuous cyclic bit pattern, or a frame code generator RG 1 for transmit- ting data information in frame format. The same conditions apply for the transmitter S2 in the Line terminal. This transmitter may either be a code transmitter KS2 or a frame code generator RG2. The receivers - M2 in the line terminal and M3 in the network terminal are also depen¬ dent on the position in the activation cycle. The receiver M2 may be a code receiver CD1 for detecting the received code pattern from the code transmitter KS1, or a frame detector RD2 for detecting data in frame format from the frame code generator RG1. The receiver M3 may

be a code receiver CD2 for detecting code patterns from the code transmitter KS2, or a frame detector RD1 for detecting data in frame format from the frame code generator RG2. The enumerated contents of the terminals relate solely to the equipment which is of importance for the activation method. The TDM technique is already known and is therefore not described.

Figure 2 illustrates the function for activation and synchronization in the subscriber terminal ST and half the network terminal NT. A se¬ quence where the activation is initiated from the subscriber side will now be described first.

A first type 4013 flipflop FF1 in the subscriber terminal ST receives on a clock input an activation request AR, e.g. in the form of a Logi¬ cal ONE signal.- The activation reqαest may be released by the subscri¬ ber Lifting the receiver, for example, if the terminal is a telephone handset. The flipflop output sends a ONE signal to the setting in¬ put on a second type 4013 flipflop FF2. The output signal from flip- flop FF2 activates the setting input on a third type 4013 flipflop FF3, the output signal of which, by connection to ENABLE inputs on a local clock pulse oscillator CL1 and to a first code generator KG1, starts transmission of clock pulse signals from the clock and trans¬ mission of a code pattern, a so-called send window from the code gene¬ rator. This generator contains a type 74 HC 161 address counter A1, to which there is connected a type 2716 PROM P1. Different types of send window are stored in the memory P1 corresponding to binary words of given appearance. The clock signals are connected to inputs on the code generator KG1 and control the burst feed-out of binary code words from the memory P1. In the selected case, the code words are 19 bits long. The code words, i.e. the send windows, are fed to a first input on a gate circuit 01, which is a type 4081 AND circuit. A second input on the AND circuit receives the output signal, i.e. the activation re¬ quest, from the flipflop FF1 via a type 4071 OR circuit 0R1. Bit bursts are sent from the output of the gate circuit 01 to the time division multiplexed bus line BL via an adapter unit IU1 for further passage through the bus to the input on the network terminal NT via a further

adapter unit IU2. The code words from the code generator KG1 are also supplied to the input on a type 4516 counter C1, which after receiving three consecutive frames sends a resetting signal to the flipflop FF1 via a second type 4071 OR circuit 0R2, the activation process then being stopped.

A first receiver unit M1 included in the network terminal NT contains a first type LM 311 threshold detector TD1, which detects the recep¬ tion of the activating code words sent from the subscriber terminal ST a- gainst a fixed threshold level. The output signal from the threshold detector activates a burst detector in the form of a fourth type 4013 flipflop FF4, the output signal of which activates the setting input on a fifth type 4013 flipflop FF5. Theoutput signal from the flipflop FF5 is applied to the ENABLE inputs on a local clock pulse osci llator CL2 and to a second code generator KG2 consisting-of -a second address counter A2, to hich there is connected a second PROM P2. A temporary synchronization of the clock in the terminal NT to the clock from the terminal ST takes place by the local clock pulse oscillator CL2 in the network terminal being controlled in phase by the output signal from the flipflop FF4.The sig¬ nal from the clock CL2 is applied to the input on the code generator KG2, in which new code words of 19 bits are generated, which are read out from the mentioned PROM P2. A word length check is made in a sync control circuit SC1 for checking the synchronization between these code words generated locally in the terminal NT and those received from the subscriber terminal ST. The circuit SC1 receives code words from the generator KG2 on a first plurality of inputs and on a second plurality of inputs the activation code words from the output of the threshold detector TD1, a check then being made that the code words on said first and second pluralities of inputs are equally in length, i.e. 19 bits according to the example. The check is carried out under control from clock pulse signals from the local clock pulse oscillator CL2. If the check is approved, i.e. if there is agreement between the code woeds, a logical ONE signal is sent from the synchronizing con¬ trol circuit as the activation request AR to the input on a transmit¬ ter log c TL1 via a second AND c rcuit 02.

The activation request on the output of the mentioned circuit 02 also activates a third OR circuit 0R3, the receiver in the terminal NT assuming an idling state by a resetting signal to the flipflop FF5 directly from the OR circuit 0R3 and by a resetting signal to the flipflop FF4 from the circuit 0R3 via a fourth OR circuit 0R4. Sync loss also leads to the idling state via the circuit 0R3. The next burst, i.e. code words from the code generator KG2, sets the burst de¬ tector FF4 to zero with the aid of the OR circuit 0R4. The burst de¬ tector is thus clear to detect new code words from the subscriber terminal ST.

As will be seen from Figure 3, the activation request AR sent from the AND circuit 02 is received on the input to the mentioned send lo¬ gic TL1. The send logic, consisting of a plurality of mutually linked logical circuits, sends control signals on an output to a two-way type 40257 data switch DS1. The latter in its first position switches through binary signals from a first code transmitter KS1. In its second position signals in frame format are switched through from a frame co¬ de generator RG1. In the mentioned activation from the subscriber, the data switch is put in a position such that a series, continuous, cyc- lie bit flow is transmitted from the sender KS1, via a sixth type

4013 flipflop FF6, through a first adaptive echo eliminator (adaptive hybrid) AG1, and through a transmission line SL to the line terminal LT on the station side. A first code receiver CD1 in the line termi¬ nal detects the incoming data flow via a second adaptive echo elimi- nator AG2 and,if an activation request is interpreted, it sends this to the station EX in the form of a log cal .ONE signal through a third AND circuit 03. The station then triggers an activation order signal AO to the input on a second send logic TL2 comprised of logical circuits in the line terminal LT. An inverter 11 interrupts the activation re- quest to the station when an activation order A0 is sent. Output sig¬ nals from the send logic activate a seventh type 4013 flipflop FF7, and also a second two-way type 40257 data switch DS2, so that data . in frame format in series form including synchronizing informations is sent out under control of the master clock pulse osci llator MCL from a second frame code generator RG2 back again to the network terminal

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NT on the subscriber side, through said seventh flipflop FF7. In its second position the data switch switches through binary information from a se¬ cond code transmitter KS2. A third local clock pulse oscillator CL3, included in the network terminal, is synchronized conventionally to the master clock pulse rate transferred in the received bit flow. For detected frame synchronizing information in a frame detector circuit RD1 there are sent control signals to the send logic TL1 to enable, as previously described, transmission of information appropriate for the moment in frame format form towards the line terminal LT. Dectec- tion of frame-synchronous information in the terminal LT is carried out in a second frame detector RD2, and is interpreted as the activa¬ tion having been successful, this being indicated towards the station EX by an approval signal RS. The circuit RD1 further passes on the activa¬ tion order signal AO to a first input on a fourth AND circuit 04. The clock signal from -the clock GL3-controls a third code generator KG3 ^~ - containing a third address counter A3 and a third PROM P3 connected thereto, both of the same types as the ones previously enumerated. In activation, the memory P3 provides a send window and a receive wind- dow. The send window is applied to the second input of the fourth AND circuit 04, the AND circuit then sending bit patterns in the form of bursts through the adapter unit IU2 and the bus line BL to the subscriber terminal ST. The receiver window form the PROM P3 is app¬ lied to a first input of a fifth OR circuit 0R5, whereon the output signal from the OR circuit is applied to the input on the receiver flipflop FF4 which is thus blocked, and prevents synchronizing flanks occuring on the flipflop output when the terminal NT sends out bit bursts itself. Such flanks must only occur when the terminal NT re¬ ceives bursts from the subscriber terminal ST. The second input of the OR circuit 0R5 is inverting and the activation order signal is app- lied to it for setting the flipflop FF4 in a stand by condition on the occasions when the activation order is not present, the receiver then being ready to receive bit bursts from the subscriber terminal.

In the subscriber terminal ST the bit bursts from the network terminal are passing through the first adapter circuit IU1 and are fed to the input on the fourth receiver M4 containing a second type LM 311 thres-

hold detector TD2. The output signal from the dectector triggers the flipflops FF2 and FF3, the output signal from flipflop FF3 then synchro¬ nizing the rate of the local clock CL1 to the rate of the station clock MCL. The clock starts the code generator KG1, send windows being read out from the memory P1 to a first plurality of inputs on a second sync control circuit SC2, which receives on a second plurality of inputs the bit pattern sent from the network terminal. Comparison is made between the word lengths as previously described, and on agreement, an activation order signal AO goes from the outputof the circuit SC2 to the subscriber installation, the logical circuits of which are thus finally activated. A resetting signal is given through a sixth OR circuit 0R6 to the flipflops FF2 and FF3 from the code generator KG1 and the synchronizing control circuit SC1, respectively, for re¬ turn to idte condition and stand by for receiving the next bit burst from the terminal NT.

In the cases where three consecutive frames have been sent towards the network terminal, or when the activation order is sent towards the sub¬ scriber, the second OR circuit 0R2 is activated and the output signal from the OR circuit stops further sending of bit bursts towards the network terminal NT by blocking the flipflop FF1.

For station-initiated activation, the acitvation order AO goes to the send logic TL2, which activates the flipflop FF7 thus enabling the transmission of a code pattern from the code transmitter KS2 towards the subscriber side. In the network terminal NT the clock CL3 is syn- chronized to the master rate from the received bit flow, the code is detected in the code receiver CD2, which then starts the code transmit¬ ter KS1. The code transmitter KS1 sends continuous, cyclic bit patterns to the station side, where the code is detected in the code receiver CD1. After detection the frame code generator RG2 sends out data in frame format and synchronizing information towards the network termi¬ nal under control of the master clock. On the subscriber side, frame format-frame synchronization is detected in the frame detector RD1, which sends out an activation order towards the subscriber, and via the send logic TL1 controls sending of frame format data from the

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frame code generator RG1 back again to the station side. In the line terminal, the frame detector RD2 detects frame format-frame synchro¬ nization and indicates by an approval signal RS to the station ^• that the connection is bit- and frame-synchronous. The activation procedure is otherwise in entire agreement with activation from the subscriber side.