The subject of the invention is a multi- -party call system service, industrial and subscri¬ ber's telephone equipment and network arranging the traffic between the individual substations without 5 central telephone exchange, moreover, the through exchange traffic of individual substations of the multi-party line networks takes place selectively. The generally applied method in commer¬ cial and domestic telephone networks is that the 0 cental telephone exchange, in consequence of the originating call, connects the line of the calling part to the line of the called part. The talk in the interconnection established this way is selective, accordingly, the other subscribers of the netv/ork 5 do not hear the talk and they can not be connected to the engaged lines.

However, there are networks, where the participant telephone sets are parallel-connected all time or in certain periods to a pair of wires. G E.g. it was accepted practice in rural telephone exchanges of manual operation that, finishing the every-day duty, theOperator had left the lines, going toward the subscribers, parallel-connected, ensuring them the callability from the direction of 5 the next sector e-change even in the operator's ab¬ sence. In case of such parallel-connected lines, the local exchange has its connecting function inter¬ rupted, and this way, the ringing signal of whichever subscriber is audible for all subscribers, and lift¬ ing the icrotelephone, they may enter the traffic

doing that, of course, without the secrecy of talks.

Though, nowadays this method is less and less applied, nevertheless even today, the multi-par- ty line arrangement of telephone sets in wre modest network, e.g. in rural networks of developing count¬ ries, or in some industrial networks of developed countries.

The multi-party line communication is gene- ral in the railway telecommunication as well. A sub¬ scriber's industrial or service multi-party line net¬ work of this kind is shown in Pig. 1, where the tele¬ phone sets T are parallel-connected via the line V to the central telephone exchange K or to the service terminal station. As a matter of course, such solu¬ tion does not offer the selectivity of talks for the subscribers.

The service telephone sets of divers carrie frequency telecommunication systems are also of multi -party line operation. The cable or wireless carrier freqqency installations are suitable for simultaneous transmission of numerous /24 ... 2700/ telephone chan nels or for transmission of television picture signal and sound signal. For instance, the signals of micre- wave telecommunication installations starting from the terminal station are received by repeater /relay/ stations, located at 20 ... SO k s from each other, and after amplification these signals are radiated again. The length of the communication line may attai several thousands kms as well, if the communication link has a lot of stations /e.g. 40-50/.

The multichannel teleohone sisnal or the

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television signal does not appear directly at the repeater stations, it is amplified only on the carrier only on the carrier wave and then radiated again toward the next station. At the same sta- tions, however, the modulating signal appears in the base-band as well; these stations repeat each other through 5-10 repeater stations. Such sta¬ tions are called as main stations, while the name of 200 ... 500 km long communication sections bet- ween two main stations is "mode -section"; the communication section of 20 ... 80 km length bet¬ ween two stations is called "radiofrequency /RE/ section".

The leader of the carrier wave telecommu- nication equipment can establish connection with the chiefs of stations via the service telephone lines; this same relates to the members of the operator staff of stations as well. Some stations of the link can be operated without personell and these stations are completed with service tele¬ phone sets too, for the personell arriving there periodically to perform checking or maintaining works.

There are two usual solutions of service telephone communication for microwave carrier frequ¬ ency telecommunication systems.

The stations within the modem section can be called through the so called omnibus communica¬ tion channels. The call is either selective, v/hen the telephone set rings only at the called repeater station, or non-selective, v/hen the personell finds out which the called station is only out of the speech heard from the stational loudspeakers.

The express service telephone sets estab¬ lish communication between the terminal stations and the main stations, generally with selective call. Both kinds of service telephone communication are 5 applied in the usual microwave telecommunication links. Common property of omnibus and express ser¬ vice telephone sets Is, that they do not ensure secret talk. Whichever station along the link can listen in the talk by lifting the microtelephone of

10 the stational service telephone set. The fundamental reason for this is, that the service telephone sys¬ tems are built up without exchange connecting two telephone sets each to other, ruling the other sets off by that.

15 The Pig. 2 shows the service telephone sys¬ tem of a microwave telecommunication equipment. The terminal stations are marked by A here, letters P mark main stations, the marks of express service line are ET, and the omnibus service lines are marked by

20 07.

The non-selective networks have already- been described in detail in connection with the ser¬ vice telephone communication systems of radio-relay installations; the term "pair of wires" is replaced

25 here by the term of radiocommunication link, but wb-± has been said here is valid for all multi-party line telephone networks /see Pig. 1/. The secrecy of talks Is required of course in public subscriber's net¬ works, although, this requirement is unsatisfied in

30 some cases. The secrecy of talks is real requirement for service telephone systems as well. Service talks between the individual stations are no business for other stations. This requirement is valid in particul

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in case of the radio-relay link leader's talk to the chief or personnel of some station.

The invention is aimed at realization of such service or industrial telephone network where the selective traffic between the stations can be organized without exchange, moreover, at realization of such subscriber's multi-party line network connect¬ ed to the central telephone exchange, where both the direct traffic between the multi-party connected sub- scribers and also their through exchange traffic can be arranged selectively. In the first place, the rea¬ lization of selective traffic v/ill be described here for serice telephone communication system, i.e. for communication without exchange. The schematic diagram of the equipment rea¬ lizing the invention is shown in Pig. 3« " e tele¬ phone set T of the multi-party substation is connected to the service line V through the controlled switch 3. This switch 3 is controlled by the logic evaluat- ing circuit 2 connected to the proper code memory 4. The busy tone generator 5 is inserted between one of points of the contjo lied switch 3 and the logic evaluating circuit 2. The code receiver 1 of the multi-party station is connected to the service line V; the output of the code receiver 1 joins the logic evaluating circuit 2.

The following working principle is shown in Pig. 3- Every substation of the invented multi- -party network has its own programmed code word. During the calling and the entire traffic the calling station transmits the code signal of the called station. All substations ox the multi-party line receive this code signal and collate it with the own programmed

code signal. The logic evaluator 2 recognizes the presence of the code signal on the line and states, that It is not identical with the one being in the proper code memory 4 , therefore, it starts the control signal to the controlled switch 3 - deconnect ing the telephone set T from the line V. At the same time the logic evaluator 2 connects the busy tone generator 5 via the controlled switch 3 to the tele¬ phone set T; i somebody lifts the microtelephone on the station, he can hear that the line is engaged. Por ensuring the continuous observability of the Susy state of the line at the uncalled, stations, dur ing the entire duration of the talk the calling sta¬ tion transmits the code signals of the called statio in cycles /e.g. several times per second/. Being cut- side the speech band. /e.g. at 3825 Hz/ and received by the code receiver 1, this code signal does not disturb the talk.

Often the service telephone network operat with selective calling systems, having the common property, that though the telephone sets connected to the line can be called selectively, the signall¬ ing ringing can only be heard at the called station, nevertheless, the traffic itself is not selective, anybody can listen in the talk.

In case of application of the selective calling system operated by coded signals, these code can adivsably be used up for forming the invented selective operation network desc i-hed^pr-ev-iously. By this solution the secrecy can be realized verj economically. The invented solution is elaborated also for the case, when besides the selective opera¬ tion of the telephone network the so called open

operation is required as well. This may occur in case of service networks. In this case, every sub¬ station has two proper code signals; the structure of such network is shown in Pig. 4. One of the out- puts of .the code receiver 1 goes to the secrecy evaluating circuit 6, while the other is connected to the logic evaluating circuit 2. One output of each evaluating circuit joins the controlled sv/itch 3 through the ITAlTD-gate 7. Purther, the doubled proper code memory 4' joins the logic evaluating circuit 2.

The equipment built-up according.to Pig. 4 operates as follows. Two code signals belong to every substations of the service network, one of them for open operation and the other for selective operation. In case ofcalling, the logic evaluator 2 and the secrecy evaluating circuit 6 estimate the callings. According to the sense of the output signals of the evaluating circuits, the controlled switches 3 - through the IT-AiTD-gate 7 - separate the telephone sets T from the line in case of calling estimated as sec¬ ret, but the set remains connected to the line in case of calling proved to be open. This version has impor¬ tant function, when the chief of the service line gives instructions simultaneously for several substa¬ tions.

The multi-party service network composed of 24 service substations and 23 selective calling devices according to Pig. 4 is schematicaly shown in Pig. 6. The telecommunication supply of rural zones, sparsely populated regions, raises a lot of technical and economical problems. The low subscriber's density and the relatively great distances increase the per capita investigantion expenses considerably. Important

part of expenses goes to build up the pairs of wires. In case of multi-party network a single pair of wires is required, or a radiochannel link. The solution offered by the invention ensures the connection of stations and the secrecy of talks. The traffic of sparsely populated regions is gene¬ rally low and - according to the CGITT manual, deal¬ ing with communication problems of rural regions of the developing countries - has the structure where each line can be used for supplying 3 ••• 10 sub¬ scribers.

The service of tv/o subscribers on a single line Is solved problem by means of a two-party line. However, the basic property of the shared telephone service is that the party members can not call each other. The multi-party subscriber's- etwork should b suitable for servicing not only more subscribers, but also the assuring of mutual callability is important requirement. The calling itself can be realized by means of some selective calling system. The inven ed solution, however, ensures the secrecy of subscriber talks as well.

The telephone talks controlled by the code signal according to the invention are applicable to the multi-party subscriber's networks, connected to exchanges and also in industrial networks connected to exchange or subexchange. The exchange-connected system of multi-party subscriber's networks is illus rated on the Pig. 5. Every subscriber has an own cal number in the central telephone exchange likewise the normal subscribers. The subscriber's connecting points of the telephone exchange 20 are not conne ed directly to the multi-party line V. The exchange located connecting substation 22 belongs to all mult

-party subscriber's substations 21 between the ex¬ change 20 and the multi-party line V. The selective calling device 23 belongs to the multi-. party sub¬ scriber's substations, while the central selective calling device 25 belongs to the connecting sub¬ stations. The structure and the operation of the connecting substation is similar to the structure and operation of individual multi-party subscriber's substations so much, that it is composed of the code receiver 1, the logic evaluator 2, the proper code memory 4 and the controlled switch 3 _> but this switch 3 connects the line ends W of the exchange 20 to the multi-party line V instead of the telephone set T. On the other hand, the connecting substation 22 does not contain the busy tone generator 5«

The selective calling devices provide the line codes both for the selective calling and the se¬ lective operation. The selective calling device 23 originates the codes by the help of the dial pulses, by means of the earthing knob of the telephone set

T; the central selective calling device 25 periodes the codes by using the ring signalling of the exchange 20.

In the system of the invented multi-party telephone networks of selective operation, in case of selective calling originated at one or other sub¬ station, the code signal of the called substation should be sent to the line after lifting the microtelephone. The code signal is received by all multi-party sub¬ stations and by the exchange-located connecting sub- station. The uncalled substations of the multi-party line, according to the above description, will be deconnected from the line. In the way, the traffic between the calling and called telephone sets of the

multi-party line becomes selective. The exchange- -located connecting substations realize that the calling is not their Business, thus, they will not perform connections and will not allow callings, arriving from the exchange to the line.

The advantage of the multi-party sub¬ scriber's system is, that the exchange regards the multi-party subscribers alike the normal subscribers. The multi-party telephone sets posses quite similar call number than the urban sets and the multi-part*- subscribers have the possibility of selecϋ ve talks. These callings do not load the exchange, the system built up of a single pair of wires or of a radio- -link is economical, the further pairs of wires can be replaced by electronic means at lower expenses. The multi-party subscriber's system is advantageous for meeting the telecommunications needs ofsparsely populated regions.

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