A SUBSCRIBER MULTIPLEXER, A TELEPHONE SYSTEM AND A METHOD FOR COMMUNICATING THE CONDITION OF A SUBSCRIBER INTERFACE

Abstract: This invention relates to a subscriber multiplexer (MUX1, MUX2) comprising means for receiving signals transmitted from subscriber interfaces (L1-L30) and feeding said signals further to a telephone exchange (1) via a PCM connection, and means for feeding signals transmitted from the telephone exchange (1) via a PCM connection further to the subscriber interfaces (L1-L30). For detecting the condition of the subscriber interfaces, the subscriber multiplexer (MUX1, MUX2) comprises measuring devices (2) for checking the condition of the subscriber interface (L1-L30) of the subscriber multiplexer, and a control means (3) for activating the measuring devices (2) in response to a measurement request signal (S1) transmitted by the telephone exchange (1) via a PCM connection, and for transmitting a message (V2) describing the measurement result to the telephone exchange. The invention further relates to a telephone system and a method for communicating the condition of a subscriber interface of a subscriber multiplexer.

Description: A SUBSCRIBER MULTIPLEXER, A TELEPHONE SYSTEM AND A METHOD FOR COMMU N I ¬ CATINGTHECONDITIONOFASUBSCRIBER INTERFACE This invention relates to a subscriber multiplexer comprising means for receiving signals tran¬ smitted from subscriber interfaces and feeding said signals further to a telephone exchange via a PCM con¬ nection, means for feeding signals transmitted from the telephone exchange via a PCM connection further to sub- scriber interfaces, and measuring devices for checking the condition of a subscriber interface of the subscri¬ ber multiplexer. The invention further relates to a telephone system comprising a telephone exchange, and a subscriber multiplexer connected to the telephone exchange by a PCM connection, the multiplexer comprising subscriber interfaces and measuring devices for checking the condition of subscriber interfaces by means of check measurements. The invention further relates to a method for communicating to the telephone exchange the condi- tion of the subscriber interface of a subscriber multiplexer connected to the telephone exchange via a PCM connection. A subscriber multiplexer is previously known the subscriber interfaces of which are connected to subscriber stations, such as telephones and similar, by means of a converter means and two-wire lines. The con¬ verter means adapts in that case the subscriber station electrically to the subscriber multiplexer, and carries out the necessary analog-to-digital conversions. The subscriber station multiplexer is connected to the tele¬ phone exchange via a PCM (Pulse Code Modulation) connec¬ tion, in which one channel of the PCM connection is allocated for each subscriber interface. The frame stru¬ cture of the PCM connection between the subscriber multiplexer and the telephone exchange is typically in accordance with CCITT (The International Telegraph and Telephone Consultative Committee) recommendation G.704, the interface of the subscriber multiplexer and the telephone exchange typically being an interface in acco- rdance with CCITT recommendation Q.512. The weakness of the above mentioned subscriber multiplexer is the difficulty in monitoring the condi¬ tion of subscriber interfaces, since monitoring the condition of a wire connected to a subscriber interface requires the visit of a maintenance person in site. The maintenance person connects a separate service terminal including measuring devices to the subscriber multiplexer, subsequent to which the maintenance person detects the condition of the subscriber interface e.g. by means of measurements of current, voltage and/or insulating resistance. Checking the condition of the interface of a subscriber multiplexer is thus a highly inconvenient and slow measure, and also relatively costly, as it requires a visit of a maintenance person in site. The object of this invention is to solve the above mentioned problems and to provide a subscriber multiplexer that allows remarkably simple checking of the condition of its subscriber interfaces. This is achieved with a subscriber multiplexer of the invention, which is characterized by comprising a control means for activating the measuring devices in response to a measu¬ rement request signal transmitted by a telephone exchange via said PCM connection, and for transmitting a message describing a measurement result to the tele¬ phone exchange, said message informing the telephone exchange that the measured subscriber interface is in order or that it is faulty. The invention further relates to a system in which the subscriber multiplexer of the invention may be utilized. The system of the invention is character¬ ized in that the subscriber multiplexer comprises: a control means which is adapted to transmit a first mess¬ age to the telephone exchange and to activate the measu- ring devices in response to the measurement request signal transmitted by the telephone exchange, and adapted to transmit a second message describing the measurement result to the telephone exchange if the subscriber interface is in order, and to wait for a time-limit signal transmitted from the telephone exchange prior to transmitting the second message if the subscriber interface is out of order. The invention further relates to a method by means of which the result of the measurement may be transmitted from the multiplexer to the telephone exchange. The method of the invention is characterized in that the measurement request signal received from the telephone exchange is acknowledged by transmitting the first message to the telephone exchange, and it is com- municated that the subscriber interface is in order by transmitting the second message to the telephone exchange, or it is communicated that the subscriber interface is out of order by transmitting the second message to the telephone exchange only subsequent to receiving the time-limit signal from the telephone exchange. The invention is based on the idea that check¬ ing the condition of subscriber interfaces is facili¬ tated and accelerated significantly when measuring devi- ces are integrated to the subscriber multiplexer, by means of which devices the operator may carry out check measurements of subscriber interfaces automatically from the operation and maintenance centre of the telephone network, and receive a message indicating the result of the measurement without this requiring a visit of a maintenance person to the subscriber multiplexer. The most remarkable advantages of the subscriber station multiplexer, the system and the method of the invention thus are that the condition of the subscriber interfaces may be detected at remarkably lower costs, more rapidly and in a simpler way compared with prior art solutions, without the signalling required for this remarkably com¬ plicating or loading the signalling of the telephone exchange or the subscriber multiplexer. In a preferred embodiment of the invention, the frame structure of the PCM connection connecting the telephone exchange and the subscriber multiplexer is in accordance with CCITT recommendation G.732, and the interface between the telephone exchange and the sub- scriber multiplexer is a V2-type interface in accordance with CCITT recommendation Q.512. In this case, the sig¬ nalling between the telephone exchange and the sub¬ scriber multiplexer pertaining to the measurement may be carried out in accordance with the invention com- pletely by using a single bit, i.e. bit c of time-slot T16 corresponding to the subscriber interface to be measured in the multiframe structure, for which bit no specific use is defined in CCITT recommendation G.732. Thus, the invention may also be utilized in prior art telephone systems in accordance with said recommenda¬ tion. The preferred embodiments of the subscriber multiplexer, the system and the method of the invention are set forth in the attached dependent claims 2-4, 6-7 and 9. In the following, the invention will be described in closer detail by means of a preferred embodiment of the invention, with reference to the attached figures, in which Figure 1 illustrates a frame structure in acco- rdance with CCITT recommendation G.732, Figure 2 shows a block diagram of the system of the invention, and Figure 3 shows a flow diagram of the progress of the test in accordance with the invention. Figure 1 illustrates a frame structure in acco¬ rdance with CCITT recommendation G. 732. Information to be transmitted both from the telephone exchange to the subscriber multiplexer and from the subscriber multiplexer to the telephone exchange is transmitted by means of a frame structure in accordance with Figure 1. It appears from Figure 1 that one multiframe consists of sixteen frames, and that one frame comprises 32 time- slots. Each time-slot, in turn, comprises 8 bits. Infor¬ mation pertaining to channels 1...30 is set in time- slots 1...15 and 17...31. Time-slot 0 is used for trans¬ mitting the synchronizing signal of the frame and time- slot 16 is used for signalling. It further appears from Figure 1 that in time- slot 16 of frame 2, signalling pertaining to channels 1 and 16 is transmitted by means of four bits a-d. In accordance with the recommendations, the values of said bits are set so that b=l, c=0 and d=l when no signalling takes place on said channels. It must be noticed that several countries, including Finland, have given recom- mendations of their own regarding the values of the above mentioned bits when no signalling takes place on a channel. For instance, according to the recommenda¬ tions given in Finland, the values of said bits are thus b=0, c=l and d=l. The value of bit c is thus totally opposite to what is supposed in the CCITT recommenda¬ tion. However, the invention will be described in the following in a case in accordance with the CCITT recom¬ mendation. The invention may, however, be applied in the Finnish telephone network with a small modification, i.e. by reversing the value of bit c from one to zero, or vice versa, in the following examples. In accordance with the invention, bit c is utilized for detecting the condition of the subscriber interfaces. In other words, if one wants to detect the condition of the subscriber interface corresponding to PCM channel 1, bit c, which is ringed in Figure 1, is used for signalling between the telephone exchange and the subscriber multiplexer. Figure 2 shows a block diagram of the system of the invention. Figure 2 shows a telephone exchange 1 (e.g. NOKIA DX210 or DX220), to which two subscriber multiplexers MUX1 and MUX2 are connected via terminals LT (Line Terminal). The subscriber multiplexers and the telephone exchange 1 are connected via a 2 Mbit/s PCM connection, the frame structure of which is in accord¬ ance with CCITT recommendation G.732, the frame struc¬ ture between the telephone exchange and the subscriber multiplexers being a digital V2 interface in accordance with CCITT recommendation Q.512. In Figure 2, thirty subscriber stations (tele¬ phones and similar subscriber stations) are connected with subscriber multiplexer MUX1 by means of two-wire lines and converter means (not shown in the figure) via interfaces L1-L30. The converter means carry out necess¬ ary analog-to-digital conversions and adapt the two-wire lines electrically to the subscriber multiplexer. There is a fixed 64 kbit/s channel available for each sub¬ scriber station connected to the subscriber interface. Accordingly, telephones and additionally an analog pri¬ vate branch exchange 5, allocating for use two of the subscriber interfaces L1-L30 of subscriber multiplexer MUX2, are connected to subscriber multiplexer MUX2. When the operator wants to detect e.g. the operational condition of the subscriber interface of subscriber multiplexer MUX1, the operator initiates manually a test cycle. In this case, the telephone exchange 1 transmits a measurement request signal to subscriber multiplexer MUX1 by setting bit c of time- slot T16 corresponding to subscriber interface LI to be measured in the multiframe structure to the value 1. In other words, in this case bit c of time-slot T16 of frame 1 shown in Figure 1 is used. Bit c is ringed in Figure 1 (the value of bit c is normally 0 according to the CCITT recommendations). A control unit 3 of subscri¬ ber multiplexer MUX1 detects that the value of said bit has changed, as a result of which it activates a measur¬ ing device 2 and transmits a first message VI to the telephone exchange also by setting in the frames to be sent towards the telephone exchange bit c of time-slot T16 corresponding to subscriber interface LI to be measured in the multiframe structure to the value 1. Subsequent to this, the measuring device 2 measures the condition of subscriber interface LI in a way known per se, e.g. by carrying out measurements of current, voltage and/or insulation resistance for the two-wire line, and by testing the condition of the con¬ verter means by means of a separate test programme. The control unit 3 monitors the progress of the measure- ments. When the measurements are completed, the control unit 3 transmits the second message to the telephone exchange by setting bit c of time-slot T16 corresponding to subscriber interface LI of the multiframe structure to the value 0 if subscriber interface LI is in order according to the measurements. If, however, the measu¬ rements indicate that subscriber interface is faulty, the control unit will wait until the telephone exchange transmits a time-limit signal S2, before it transmits the second message V2 to the telephone exchange 1. Subsequent to transmitting a measurement request signal SI, the telephone exchange 1 monitors the value of said bit c in the frames received from the subscriber multiplexer. When the telephone exchange 1 detects that the value of said bit has changed to one (the first message VI), it starts a timer. When the timer indicates that a certain predetermined time has expired, the telephone exchange detects that the test has failed, i.e. that the subscriber interface in ques- tion is faulty (unless it has received a second message V2 by that time), and it transmits a time-limit signal S2 to the subscriber multiplexer, by setting said bit c to the value 0. Figure 3 shows a flow diagram of the progress of the test in a system of the invention. When the oper¬ ator has started the test in block A, the telephone exchange transmits a measurement request signal SI in block B (i.e. bit c is set to the value 1) to the sub¬ scriber multiplexer. The subscriber multiplexer acknowl- edges the start of the test in block C by transmitting a first message VI to the telephone exchange (i.e. bit c is set to the value 1). This means that the measuring device of the subscriber multiplexer starts testing the subscriber interface. When the exchange receives the first message, it initiates time supervision in block D. The telephone exchange has received in advance the information on how long the test is expected to last. If the time in question expires, the exchange states that the test has failed due to a faulty subscriber interface and transmits the time-limit signal S2 (i.e. bit c is set to the value 0) to the subscriber multiplexer in block E. The subscriber multiplexer ackn¬ owledges the time-limit signal with a second message V2 (i.e. bit c is set to the value 0) in block F, subse- quent to which the test is ended in block G. If, however, the measured subscriber interface of the subscriber multiplexer is in order, the sub¬ scriber multiplexer transmits the second message V2 (i.e. bit c is set to the value 0) to the telephone exchange in block H. The telephone exchange acknowledges the second message in block I by transmitting the time- limit signal S2 (i.e. bit c is set to the value 0) to the subscriber multiplexer, subsequent to which the test is ended in block G. Thus, the information on the condition of the subscriber interface of the subscriber multiplexer may be transmitted to the exchange by allocating a single bit per channel, i.e. bit c of time-slot T16. The infor¬ mation received at the exchange only indicates whether the subscriber interface is in order or not, after which more accurate information is obtained only when a main¬ tenance person has tested the subscriber multiplexer in site. It should be understood that the above descrip- tion and the figures associated therewith are only intended to illustrate the present invention. Different variations and modifications will be obvious for persons skilled in the art, without deviating from the scope and the spirit of the invention set forth in the attached claims.

Claims: Claims : 1. A subscriber multiplexer (MUX1, MUX2) com¬ prising means for receiving signals transmitted from subscriber interfaces (L1-L30) and feeding said signals further to a telephone exchange (1) via a PCM connec¬ tion, means for feeding signals transmitted from the telephone exchange (1) via a PCM connection further to subscriber interfaces (L1-L30), and' measuring devices (2) for checking the condi¬ tion of a subscriber interface (L1-L30) of the subscrib¬ er multiplexer, c h a r a c t e r i z e d in that the subscriber multiplexer (MUX1, MUX2) comprises control means (3) for activating the measuring devices (2) in response to a measurement request signal (SI) trans¬ mitted by the telephone exchange (1) via said PCM con¬ nection, and for transmitting a message (V2) describing a measurement result to the telephone exchange, said message (V2) informing the telephone exchange (1) that the measured subscriber interface (L1-L30) is in order or that it is faulty. 2. A subscriber multiplexer as claimed in claim 1 in which the frame structure of said PCM connection is in accordance with CCITT recommendation G.732, and in which the interface between the telephone exchange (1) and the subscriber multiplexer (MUX1, MUX2) is a CCITT Q.512 V2 type interface, c h a r a c t e r i z e d in that the control means (3) comprises means for rece¬ iving the measurement request signal (SI) from the tele¬ phone exchange (1) in time-slot T16 of a multiframe structure, and for transmitting a message (V2) describ- ing the measurement result to the telephone exchange in time-slot T16 of the multiframe structure. 3. A subscriber multiplexer as claimed in claim 1 or 2, c h a r a c t e r i z e d in that a subscriber station is connected to the subscriber interface (Ll- L30) by means of a converter means and a two-wire line. 4. A subscriber multiplexer as claimed in any of the claims 1-3, c h a r a c t e r i z e d in that the measuring devices (2) comprise means for carrying out measurements of current, voltage and/or insulation resistance for the subscriber interface. 5. A telephone system comprising a telephone exchange (1), and a subscribermultiplexer (MUX1, MUX2) connected to the telephone exchange by a PCM connection, the multiplexer comprising subscriber interfaces (L1-L30) and measuring devices (2) for checking the condition of the subscriber interfaces (L1-L30) by means of check measurements, c h a r a c t e r i z e d in that the subscriber multiplexer comprises: a control means (3) which is adapted to trans¬ mit a first message (VI) to the telephone exchange (1) and to activate the measuring devices (2) in response to a measurement request signal (SI) transmitted by the telephone exchange (1), and adapted to transmit a second message (V2) describing the measurement result to the telephone exchange (1) if the subscriber interface (Ll- L30) is in order, and to wait for a time-limit signal (S2) transmitted from the telephone exchange (1) prior to transmitting the second message (V2) if the sub¬ scriber interface (L1-L30) is out of order. 6. A system as claimed in claim 5, in which the frame structure of the PCM connection is in accordance with CCITT recommendation G.732 and in which the inter- face between the telephone exchange (1) and the sub- scriber multiplexer (MUX1, MUX2) is a V2 type interface in accordance with CCITT recommendation Q.512, c h a r ¬ a c t e r i z e d in that the telephone exchange (1) is adapted to transmit the measurement request signal (SI) and the time-limit signal (S2) to the control means (3) in time-slot T16 of the multiframe structure, and that the control means (3) of the subscriber multiplexer (MUX1, MUX2) is adapted to transmit the first and the second message (VI, V2) to the telephone exchange (1) in time-slot T16 of the multiframe structure. 7. A system as claimed in claim 5 or 6, c h a - r a c t e r i z e d in that the telephone exchange (1) comprises means for transmitting the time-limit signal (S2) to the subscriber multiplexer (MUX1, MUX2) when a predetermined time has passed from transmitting the measurement request signal (SI) unless the telephone exchange (1) has received the second message (V2) by that time. 8. A method for communicating to a telephone exchange the condition of the subscriber interface (Ll- L30) of a subscriber multiplexer (MUX1, MUX2) connected to the telephone exchange (1) via a PCM connection, c h a r a c t e r i z e d in that a measurement request signal (SI) received from the telephone exchange (1) is acknowledged by transmit¬ ting a first message (VI) to the telephone exchange (1), and it is communicated that the subscriber inter¬ face is in order by transmitting a second message (V2) to the telephone exchange, or it is communicated that the subscriber interface (L1-L30) is out of order by transmitting the second message (V2) to the telephone exchange (1) only subsequent to receiving a time-limit signal (S2) from the telephone exchange (1). 9. A method as claimed in claim 8, in which the frame structure of the PCM connection is in accordance with CCITT recommendation G.732 and in which the inter¬ face between the telephone exchange (1) and the sub- scriber multiplexer (MUXl, MUX2) is a V2 type interface in accordance with CCITT recommendation Q.512, c h a r ¬ a c t e r i z e d in that the telephone exchange (1) is adapted to transmit the measurement request signal (SI) by setting bit c of time-slot T16 corresponding to the subscriber interface to be measured in the multifra¬ me structure to the value 1, in that bit c of time-slot T16 corresponding to the subscriber interface to be measured in the multiframe structure is set to the value 1 for transmitting the first message (VI) to the tele- phone exchange (1), that bit c of time-slot T16 corre¬ sponding to the subscriber interface to be measured in the multiframe structure is set to the value 0 for tran¬ smitting the second message (V2) to the telephone exchange (1), and that the telephone exchange (1) is adapted to transmit the time-limit signal (S2) by set¬ ting bit c of time-slot T16 corresponding to the sub¬ scriber interface to be measured in the multiframe stru¬ cture to the value 0.

Inventors: TIAINEN VESA, TIIHONEN ARTO, TIAINEN, VESA, TIIHONEN, ARTO
Applicants: NOKIA TELECOMMUNICATIONS OY, TIAINEN VESA, TIIHONEN ARTO, TIAINEN, VESA, TIIHONEN, ARTO
Application year: 1995
Main classification: H04J3
IPC codes: H04J3, H04M3, H04Q3, H04Q11