IE50017B1

IE50017B1 - Digital telephone system

Info

Publication number: IE50017B1
Application number: IE875/80A
Authority: IE
Original assignee: Telefonbau & Normalzeit Gmbh
Priority date: 1979-04-30
Filing date: 1980-04-29
Publication date: 1986-02-05
Also published as: DE2917572C2; AU5786280A; EP0018526A1; DE2917572B1; EP0018526B1; ATE4364T1; IE800875L

Abstract

1. Method of operating digital main terminals (H) and/or branch exchanges (NST) connected to a PCM exchange (V), whereby the subscribers lines (AL) are connected with line distributors (LVZ) each having a line circuit (LE) as interface to the PCM-line system (LS) for the connection with the exchange (V) and the time slots of the PCM-line system are distributed by a demultiplexer and the contained information is retransmitted to the concerning subscriber's lines (AL) and the incoming information on the subscriber's lines (AL) is retransmitted via the concerning time slots of the PCM-line system by a multiplexer, and additional equipment (for example second telephone station (Z), extensions (N), etc) is connected via internal terminal lines (IAL) with the main terminals (H) and/or branch exchanges (NST) of the subscriber's lines (AL), and all information coming in on the subscribers line (AL) is retransmitted on the internal terminal line (IAL) and vice versa, whereby on the subscriber's lines (AL) data words are transmitted each consisting of a PCM-word and additional bit for the transmission of additional information (for example synchronisation signals, signalling signals, metering pulses, etc) and the bit rate on the subscriber lines (AL) is higher than the normal transmission rate on the one or multiple channel PCM-lines and the signalling signals are transmitted via the PCM-line system (LS) in both directions in the respective signalling time slots whereas the synchronisation signals of the subscriber's lines (AL) are excluded from the transmission on the PCM-line system (LS), characterized in, that the same frame format is used both on the subscriber's lines (AL) and the internal terminal line, whereby the additional bit are provided for the transmission of internal signalling signals (I), external signalling signals (E), synchronisation signals (S, ES, IS) and one additional service channel (D) on the subscriber's lines (AL) and the internal terminals lines (IAL), whereby the internal signalling signals (I) which are being used exclusively on the internal terminal line (IAL) and the synchronisation signals (S, ES, IS) are excluded from the retransmission to the exchange (V) in the line distributor (LVZ), whereas the service channel (D) is transposed to a time slot of the PCM-line system (LS) and vice versa.

Description

The invention relates to digital telephone systems and especially to line distributors and to a procedure for the connection and operation of digital telephone stations as main stations and/or digital private automatic branch exchanges (PABX'es) with a PCM-exchange, in which the subscriber lines and/or the trunk lines are connected to the line distributors and each line distributor is connected to the PCMexchange via a PCM-line system. Each line distributor is provided with a demultiplexer for distribution of information carried by the channels of the PCM-line system in the incoming direction to the subscriber lines and/or to the trunk lines and with a multiplexer for collection of information arriving on the subscriber lines and/or on the trunk lines for transmission on the PCM-line system to the exchange. To the individual PCM-words on the subscriber lines and/or on the trunk lines, additional bits are added for the transmission of additional information, and the transmission rate is higher than the transmission rate of the normal 8-bit PCM words used in the PCM-line system.

Concentrators are used for the concentration of subscriber traffic to a value which allows economical transmission. In the magazine of the Swiss Postal Administration Technische Mitteilungen PTT 12/1973 on pages 554 to 578, an integrated PCM-system is described in which digital telephone stations, data terminals, and facsimile units, etc, are connected to a so-called digital concentrator. On the digital subscriber line a 10-bit code is used which carries an 8-fait PCM-word and two bits for the transmission of a code combination for signalling.

In the CCITT-Document GM/NRD - No. 64-E entitled Envelope Structure and Digital Subscriber Line, more details are disclosed concerning the transmission of PCM-words and additional bits for signalling. The bit rate for the transmission of the PCM-words on a so-called one-channel subscriber line is normally 64 kbit/s. When two additional bits are included in the transmission of PCM words, the bit rate is raised to 80kbit/s, the scanning frequency of 8kHz being maintained.

It has been already proposed to install additional equipment such as a second bell, a second telephone station, data terminals etc. for a digital telephone station which is operated as a main station. This equipment is connected to the main station by an internal line, information arriving at the main station on the subscriber line being retransmitted to the internal line by the main station, and, in the opposite direction, information transmitted on the internal line by units of the additional equipment being retransmitted to the subscriber line via the main station.

An object of the invention, therefore, is to provide for connec25 tion and operation of telephone stations and PABX’es for operation with a digital exchange, using additional bits for transmission of additional information on the subscriber and trunk lines.

According to the invention, there is provided a procedure for S0017 the operation of digital main telephone stations and/or PABX'es with a PCM-exchange, terminal lines connecting said stations or PABX'es to line distributors and each line distributor being provided with a line circuit as interface to the PCM-line system for connection to the exchange, the channels of the line system being separated by a demultiplexer, information carried by the line system being transmitted to respective terminal lines and incoming information on the terminal lines being transmitted to respective channels of the line system by a multiplexer, the equipment connected to the terminal lines being connected to internal lines and information arriving on the terminal lines being retransmitted to the internal lines and vice versa, and additional bits for. the transmission of additional information being added on the lines beside the individual information-carrying PCM-word and a higher transmission rate being used, wherein the additional bits are used within a frame consisting of a defined number of data words (PCM-words plus additional bits) for the transmission of internal and external signalling characters, synchronisation signals and an additional service channel, the internal signalling characters and the synchronisation signals being excluded from the transmission to the exchange, while the external signalling characters are transposed to the signalling channel assigned to the respecof the line system tive channel/and the service channel is transposed if necessary to another channel of the PCM-line system, or vice versa. This is performed by the line distributor installed between the exchange - to which it is connected via a PCM-line system - and the telephone station and/or the PABX'es - to which it is connected via subscriber lines or trunk lines. Said line distributor not only has the task of transposition of information arriving on the subscriber line or trunk line to the PCM-line system and vice versa but it is also used for the separation of information transmitted by the digital telephone station or PABX, which may reach the subscriber line or trunk line.

In the distribution of transmissible information carried by two additional bits within a frame consisting of 16 data words, the 32 additional bits may advantageously be subdivided into: a) external signalling - 4 bits b) internal signalling - 8 bits c) synchronisation - 4 bits d) service channel - 16 bits With a frame formed by 16 data words, an external signalling character having a word length of 4 bits may easily be inserted into a signalling channel of the PCM-line system, since the latter is available after each 16 frames for each channel or time slot. The service channel is used for the additional and simultaneous transmission of information which is intended for or generated by data terminals of the main station in question.

In an alternative subdivision, the additional 32 bits within a frame consisting of 16 data words may carry the following information: signalling 4 bits signalling 4 bits synchronisation - 4 bits synchronisation - 4 bits :hannel 16 bits c) service channel the information under b) and d) being excluded from retransmission to the exchange. By the use of an additional 4 bits for transmission of synchronisation signals on the subscriber or trunk line, greater security for recognition of synchronisation signals may be achieved, since possibly greater interference on the line must be taken into account.

The invention may advantageously encompass the use of a terminal distributor which is looped into the subscriber line for the addition or 0017 separation of the service channel, service channel information being transmitted via a special line to or from one or more units of additional equipment of the main station in question. These units may include a burglar alarm, a fire alarm, distress alarm units, etc, or an automatic reading device for household electricity or gas meters, or a siren control for air raid warning systems.

According to another feature of the invention, external signalling may use 8-bit words, transmission to the exchange and from the exchange via the PCM-line system using one double multifrarae and the indicator bit of the signalling word changing its information at each multiframe of even number. When the number of representable information characters is insufficient using signalling words of 4-bit length, the character supply may be enlarged by the addition of an additional 4 bits for the transmission. The transmission is performed by each two successive multiframes. For recognition of the first part of the 8 bit signalling word, the indicator bit is changed correspondingly.

The invention may also provide for the transmission of several data words of different channels of one frame by the line distributor via a subscriber line or trunk line and vice versa. For connection of a small PABX with a trunk line it is possible to operate the line in question as a four-channel line instead of as a one-channel line.

The above and other features of the invention will now be described in detail with reference to the accompanying drawings in which: Fig. 1 is a block diagram of an exchange system with digital telephone stations, line distributors and PABX'es and Fig. 2 is a diagram showing the organisation of a frame used for transmission on the subscriber or trunk line and the transposition of the carried information to a frame or multi-frame of the PCM-line system.

Fig. 1 shows an exchange V which is connected to line distributors LVZ via PCM-line systems LS. The latter are regular PCM-30-systems. The connection of digital telephone stations being operated as main stations H and PABX'es is performed by the terminal lines AL, These are subscriber or trunk lines and may be operated either as one-channel (ALl) or as multichannel (AL4) lines.

For incoming PCM-words via the respective PCM-line systems LS, each line distributor LVZ is provided with a demultiplexer for distribution to the lines AL. For the outgoing direction, the line distributor LVZ is provided with a multiplexer for insertion of PCM-words arriving on the lines AL into corresponding channels of the PCM-line system. Furthermore in each line distributor LVZ, means are provided for retransmission of information on the signalling channels of the PCM-line system LS to the lines AL and vice versa. A digital telephone station may be connected and operated as a main station H. It is also possible to install a second (Z) telephone station for the main station H. The digital telephone station is in any case provided with an additional pair of terminals for connection of an internal line for operation of additional equipment, information arriving on line AL being retransmitted to the internal line and vice versa. The internal line renders possible the operation of a second telephone station Z, an additional bell, an answering unit,or data terminals such as data displays, facsimile units, etc., the second telephone station being operable as an extension. A main station H may also be operated exclusively as a data terminal, a data terminal having to be connected to line AL instead of a telephone station. As interface, a modem is provided.

The normal 8-bit PCM-words are suitable for the transmission of speech signals or other digital information. By the use of an additional service channel on a line AL, additional equipment HE of the main station H may be operated via line ALH, This additional equipment may be for example a burglar alarm, a fire alarm, a distress alarm, an automatic reading device for household electricity or for gas meters, or a siren control for air raid warning systems, etc. The insertion of the additional service channel into the information flow on line AL is performed by a looped-in terminal distributor AVZ. Because the feeding of the equipment connected to line AL is performed via line AL, the terminal distributor is provided with its own power supply in order to avoid an additional load on the line distributor LVZ. If the power supply breaks down, line AL within the terminal distributor AVZ is switched through automatically to the main station H.

PABX'es may be connected to the respective line distributor LVZ via a multi-channel line AL4 carrying a number of different channels (PABX A), via several single-channel lines AL1 (PABX B), or via a PCM-30-line system (PABX C), The PABX itself may be a digital PABX with digital telephone stations N or an analog PABX with corresponding interfaces for line AL. The PABX has its own power supply, a telephone station N being connected automatically to line AL in case of power failure. Contrary to the PCM-line system LS using PCM-words of 8-bit length, the word length on line AL is 10 bits, 8 bits containing the actual PCM-signal and the remaining 2 bits being used for the transmission of additional information. Fig. 2 shows a frame R consisting of 16 words W each having 10 bits, for one channel of line AL. The same data format is used on internal lines. With a frame length of 16 words, 32 bits are available for the transmission of additional information within a frame. The information can be subdivided for example according to the following pattern: - 8 50017 bits for external signalling E 8 bits for internal signalling I 4 bits for synchronisation S 16 bits for a service channel D The internal signalling information I and the synchronisation information S are only necessary for the operation of equipment connected to the internal line. Because all information on the internal line is also retransmitted to line AL, it also arrives at the line distributor LVZ. Because this information is not required at the exchange V, it is excluded from retransmission by the line distributor LVZ.

The information for the external signalling E, which is necessary for control of the establishment and termination of connections within the exchange V, is transposed by the line distributor LVZ to the signalling channel assigned to the respective channel of the PCM-line system LS.

The normal PCM-30-line systemprovidesasignalling channel of 4-bit length for each channel within a multiframeURV consisting of 16 frames R.

This signalling channel is used for the transmission of the external signalling information E, which has a length of 4 bits.

When a word length of 4 bits is insufficient for the transmission, the character supply may be extended by the use of signalling words of 8-bit length, each half (4 bits) being transmitted in one multiframe URV, and two multiframes URV forming a double multiframe. Marking of the first half of the word may be achieved by alternation of the information of the indicator bit, which changes with each multi frame URV.

Because of the great number of lines AL, they cannot be installed as high quality cables for economic reasons. Furthermore in the case of the lines AL, by contrast with the PCM-line systems, disturbances may be expected which might cause failures of the information content of individual data words. By the provision of an additional 4 bits for the transmission of synchronisation signals, the problem may be solved, a total of 8 bits being available within a frame RA on line AL (external synchronisation - 4 bits, and internal synchronisation - 4 bits). This ensures a faster synchronisation operation. The internal signalling has to be reduced to 4 bits in this case.

The service channel D is used for transmission of additional data for the operation of additional equipment, the transmission being performable simultaneously with speech signals. The 16 bits of a frame RA are retransmitted to an additional free channel of the PCM-line system LS by the line distributor LVZ. Because these 16 bits of the service channel D use only 2 channels within one multiframe URV of the PCM-line system, the remaining 14 channels may be used by service channels of other lines AL. This may be performed either by using a random free channel causing a complicated control structure in the line distributor LVZ, or by the use of defined channels of the PCM-line system LS, which are reserved for the transmission of service channel information. Both operations are performed within the line distributor LVZ. The latter case causes limitation of the channels available for speech transmission but requires simpler control within the line distributor LVZ. Lines AL are two-wire lines being operated in full duplex. This means that the interfaces of the lines AL in the line distributor LVZ and in the telephone stations and PABX'es must be provided with corresponding burstmode transmission circuits. Transmission of individual 10-bit data words on line AL is performed by the alternate transmission in both directions, a data word transmitted in one direction being followed by the transmission of a data word in the opposite direction, so that immediately after the termination of the transmission of a data word, the receiver of the sending side is activated. As soon as a data word arrives from the - 10 50017 opposite direction, transmission of the next data word can be started.

In order to ensure safe operation of all units, the signalling information is transmitted repeatedly in succession, namely as long as reception is acknowledged by the receiving side. The transmission rate on line AL has to be higher than that on the PCM-line system LS because of the propagation time caused by the length of line AL. The operation of full duplex on a dual-wire terminal line is described in detail in for example the Proceedings 1978 International Zurich Seminar on Digital Communication on pages C5.1 to C5.4.

Claims

1. A procedure for the operation of digital main telephone stations and/or PABX'es with a PCM-exchange, terminal lines connecting said to line stations or PABX'es'distributors and each line distributor being provided with a line circuit as interface to the PCM-line system for connection to the exchange, the channels of the line system being separated by a demultiplexer, information carried by the line system being transmitted to respective terminal lines and incoming information on the terminal lines being transmitted to respective channels of the line system by a multiplexer, the equipment connected to the terminal lines being connected to internal lines and information arriving on the terminal lines being retransmitted to the internal lines and vice versa, and additional bits for the transmission of additional information being added on the lines beside the individual information-carrying PCM-word and a higher transmission rate being used, wherein the additional bits are used within a frame consisting of a number of data words (PCM-words plus additional bits) for the transmission of internal and external signalling characters, synchronisation signals and an additional service channel, the internal signalling characters and the synchronisation signals being excluded from the transmission to the exchange, while the external signalling characters are transposed to the signalling channel assigned to the respective channel of the line system and the service channel is transposed if necessary to another channel of the PCM-line system, or vice versa.

2. A procedure according to claim 1, wherein two additional bits are used for each word within a frame consisting of 16 data words, to provide 32 bits for transmission of information, divided as follows: a) external signalling - 4 bits b) internal signalling - 8 bits - 12 50017 c) synchronisation - 4 bits d) service channel -16 bits

3. A procedure according to claim 1, wherein two additional bits are used for each word within a frame consisting of 16 data words to 5 provide 32 bits for transmission of information, divided as follows: a) external signalling - 4 bits b) internal signalling - 4 bi ts c) external synchronisation - 4 bits d) internal synchronisation - 4 bits θ) service channel - 16 bits the information under b) and d) being excluded from retransmission to the exchange.

4. A procedure according to claims 1 to 3, wherein the service channel is added in or separated out by a terminal distributor looped 15 into the terminal line, and information transmissible on the service channel is transmitted via a special line to equipment assigned to a respective main station and the incoming information from said equipment is retransmitted on the service channel.

5. A procedure according to claims 1 and 2, wherein 8 bits are 20 used for external signalling and a double multiframe of the PCM-line system is used for transmission to the exchange, the indicator bit of the signalling word alternating its information in each multiframe of even number.

6. A procedure according to any of claims 1 to 5, wherein the data 25 words of several channels of a single frame are each transmitted to a terminal line and vice versa by the line distributor,

7. A procedure according to claims 1 to 4, wherein the service channels of several terminal lines are transmitted via a common channel - 13 50017 of the PCM-line system to the exchange and vice versa.

8. A procedure according to claims 1 and 7, wherein certain channels of the PCM-line system are defined for transmission of service-channel information,said certain channels being excluded from the transmission of 5 PCM-words and the service channels of a certain number of terminal lines being transmitted via an assigned channel.

9. A procedure according to claims 1 to 8, wherein signalling information of the terminal lines is transmitted repeatedly as often as it is acknowledged by the receiving side.

10. Io. A procedure for the operation of digital main telephone stations and/or PABX'es substantially as described herein with reference to the accompanying drawings.