Abstract:
A telephone communication system comprising a plurality of intercoupled sub-systems each of which comprises a control-unit and at least one peripheral module to which multiple terminals are connected. The control-unit of each sub-system includes destination numbers identifying the terminals within the system, and from the destination number provided by a source terminal determines with which sub-system the destination terminal is associated. When the destination terminal sub-system differs from the source terminal sub-system, signalling information identifying the source terminal is transmitted to the control-unit of the destination terminal sub-system. The control-unit of the destination terminal sub-system then analyzes such information and establishes the connection to the destination terminal therein.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a telecommunication system, in particular a telephone system comprising a plurality of intercoupled sub-systems, each sus-system comprising a switching system, a control-unit and at least one peripheral module, to which communication lines can be connected. 
     2. Description of the Prior Art 
     Such a telecommunication system is generally known. In a telecommunication network of sub-systems found in industrial telephone exchanges the network is normally composed of independent sub-systems, each of which manages the variable (and semi-variable) permanent data of its own connections. It is often unavoidable that each data system must also comprise &#34;global net data&#34; such as routing data and data concerning the presence or absence of teleprinters. Consistency problems may then occur when the network has to be approached as a whole by operational maintenance in order to change the data. 
     A further problem is that in distributing interrelated data about the sub-systems the data management becomes particularly complicated, for example, by relation variations. It may then also occur that data relating to connections must be derived from various places, which gives rise to delays and, moreover, brings about a higher input/output activity of the control-unit. 
     SUMMARY OF THE INVENTION 
     The invention has for its object to provide a telecommunication system of the kind set forth in the preamble by which effective and economic data management is created in a simple manner. The telecommunication system is characterized in that the control-unit of each sub-system has a list of the destination numbers inside the system, that on the basis of a destination number provided by a source connected to a peripheral module via a communication line, it is determined with which sub-system the destination is associated, which destination is connected to a peripheral module via a communication line, and that when the destination sub-system differs from the source sub-system the necessary (signalling) information about identity and characteristics of the source is transmitted to the control-unit of the destination system and the connection is passed on to the destination sub-system and in that the control-unit of the destination sub-system analyzes said information and, as the case may be, establishes the connection with the destination. 
     When the destination is to be diverted (for example in the case of a diversion because of non-response) the destination sub-system transfers, in accordance with the invention, the information about the new destination to the control-unit of the sub-system to which the new destination is associated through the control-unit of the source sub-system. 
     The invention also provides a method of outgoing call assistance by an operator in a sub-system other than the source terminal and destination terminal sub-systems. 
     It is advantageous for the sub-systems to be coupled with multiplex lines, which include at least one channel for transferring signalling information. 
     It is furthermore advantageous for said channel to be a 64k bit/s common channel signalling channel inside a 2 Mbit/s multiplex line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention and their advantages will be set out with reference to the accompanying drawings, in which corresponding elements are designated by the same reference symbols. In the drawings 
     FIG. 1 is a block diagram of a telecommunication system embodying the invention and comprising three sub systems, 
     FIG. 2 a block diagram of part of a telecommunication system for illustrating signalling a terminal in accordance with the invention, 
     FIG. 3 a block diagram of part of a telecommunication system for illustrating ringing when diverting a connection in accordance with the invention, 
     FIG. 4 a block diagram of part of a telecommunication system for illustrating the operator&#39;s handling of an outgoing connection in accordance with the invention, and 
     FIG. 5 a block diagram of part of a telecommunication system for illustrating the operator&#39;s handling of an outgoing connection to a non-free terminal in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a telecommunication system comprising three sub-systems DS 1 , DS 2  and DS 3 . The sub-systems are connected by intersystem-lines IL 12 , IL 23  and IL 13 . Each sub-system comprises a switching network SN and one or more peripheral modules PM serving to connect subscriber lines SL to the switching network SN concerned. Further more each sub-system comprises a control unit MCU, which is also connected to the switching network SN. To the subscriber lines may be connected a telephone set, a terminal, a graphical display unit or other terminal apparatus. Depending on the size of the system the system may comprise a single T stage or a TST (in general a TnST) network. 
     The establishment of a connection between two terminals connected to the system takes place as follows. If a terminal T S , the source terminal connected to sub-system DS 1 , desires a connection to terminal T D , the destination terminal connected to sub-system DS 3 , the desired connection of the source is announced - in a further conventional manner - through the peripheral module PM 1  to the switching network SN 1  to the control-unit MCU 1  of the sub-system DS 1 . The characteristics and the identity of the source and the identity of the destination are determined in the control-unit MCU 1 . It is in particular determined to which sub-system the destination is connected. For this purpose each control-unit has a list indicating which terminal numbers are associated with which sub-systems. If it is found that the destination is in a different sub-system--in this example the destination being in sub-system DS 3  --the control-unit MCU 1  of the first sub system DS 1  transfers the required information about the identity and characteristics of source and destination to the processing unit of the sub-system with which the destination is associated (MCU 3 ). The transfer of this information is performed through the intersystem lines interconnecting the subsystems, in this example the intersystem line IL 13 . In addition the connection between the source and the destination sub-system is established which means that a path is created from terminal T S  via peripheral modules PM 1 , through switching network SN 1  and via intersystem line IL 13  to the switching network SN 3  of sub-system S 3 . In sub-system DS 3  a connection is then established between the destination T D  and the appropriate input of the switching system SN 3 . The establishment of this connection is in fact, for the sub-system SN 3  nothing else than the establishment of a connection between two parts (source an destination) connected, so to say, to the same sub-system, since the sub-system itself contains all information required for making the connection with that sub-system and owing to the further switching of the source sub-system the source is, so to say, displaced to an input of the destination sub-system. 
     The intersystem lines may be multiplex lines having a transmission capacity of 2 M bit/s, subdivided into 32 channels of 64k bit/s each. One (or more) of these channels is (are) reserved for the transmission of the (signalling) information. 
     Although FIG. 1 shows three sub-systems, the invention is not limited thereto; it may be fewer or more than three systems. It is also possible of the inter-system lines to be formed by a bundle of two or more parallel lines. Moreover, complete interconnectability is not strictly necessary. 
     The features of the invention will now be described more fully with reference to a few practical situations. 
     FIG. 2 shows the interconnection operation for a trunk line TRK (connected to source terminal TS), which is connected through the peripheral module PM A  of the sub-network DS A , the switching system SN A  and the intersystem line IL AB  to the switching network SN B  of sub-system DS B . After the control-unit MCU B  of the sub-system DS B  has assessed that the destination terminal T D  is &#34;free&#34;, the T stage T B  forming part of the peripheral module PM B  of the sub-system DS B  applies from an input RT a ringing tone to the source T S . The destination T stage itself provides the ringing tone to the destination terminal T D . The response destination terminal T D  is then connected to the T stage of the peripheral module PM B  and is switched on (indicated by broken lines in FIG. 2) so that at the same time the ringing tone for the two parties is interrupted. 
     If during ringing the destination terminal T D  has to be changed over in the case of non-response to another destination terminal T&#39; D , which is associated with a different sub-system DS C , a situation as illustrated in FIG. 3 occurs. Through input RT of the T stage of peripheral module PM B  the source terminal T S  is uninterruptly rung. The control unit MCU B  of sub-system DS B  transmits the new location of the destination terminal T&#39; D  to the control-unit MCU A  of the source system DS A . This control-unit (MCU A ) transfers through the intersystem line IL AC  the (signalling) information to the sub-system DS C  with which the destination T&#39; D  is associated and then switches further connection to that sub-system. The sub-system DS C  emits ringing current to destination terminal T&#39; D . When the destination terminal T&#39; D  responds, the reply signal is rapidly transferred to the sub-system DS A , after which in the switching network of the source system DS A  a change-over takes place to the connection indicated by broken line. In the T stage of the peripheral module PM C  of the destination sub-system DS C  the connection indicated by broken line is established. An advantage of this way of ringing is that the rhythm of the ringing tone for the source terminal T S  remains unvaried, since the ringing tone continues emanating from the sub-system DS B . 
     FIG. 4 illustrates the outgoing call assistance by an operator. The terminal T S  and the source sub-system DS A   desire an outgoing (trunk) connection. In principle, the three parties concerned i.e. the source, the destination and the desired trunk may be located in three different sub-systems. The control-unit of the sub-system DS A , with which the terminal T S  is associated, transmits in the manner described above the (signalling) information to the control-unit of the sub-system DS B  with which an operator OPR is associated. The connection is switched on so that the operator can communicate with terminal T S  through the T stage T A  of the peripheral module PM A  of the source sub-system DS A , in a path through switching network SN A , the intersystem line IL AB , a path through the switching network SN B  of the sub-system DS B  with which the operator is associated, the T stage T B  of said sub-system and the operator. The operator will then establish a connection to an outgoing trunk circuit TRK through the source sub-system DS A  to the sub-system DS C  with which is associated the destination T D . In other words there is not established a direct connection from sub-system DS B  to sub-system DS C . Instead this connection is formed by a path through the T stage T B  of the peripheral module PM B , to which the operator is connected, by a path through switching system SN B , the intersystem line IL BA , a path through the switching system SN A , the intersystem line IL AC , a path through switching system SN C  and finally through the trunk circuit TRK to the destination T D . Upon response by the destination T D  the dotted connection RUP (reserved ultimate path) is made in the switching system SN A  of the source sub-system DS A . It is also possible to switch in two steps: upon responce by the destination T D  first a dotted connection RPP (reserved provisional path) can be made in the operator sub-system DS B  effectively short-circuiting the connections to operator sub-system DS B  and only then the connection RUP is made in the source sub-system DS A . An advantage of this manner of establishing an outgoing connection is that the connections are made so that the final condition is as simple as possible. Moreover, rapid response to the operator handling is thus ensured. 
     Although the Figure shows two different intersystem lines between the sub-systems DS A  and DS B  (i.e. IL AB  and IL BA ) this is not necessary; the connection may be formed either by two channels on one multiplex line or by one channel on such a line designed for two direction traffic. Moreover, as stated above, the intersystem lines include one or more common channel signalling channels and a number, for example, 30 of communication channels. 
     FIGS. 4 and 5 omit the control units which are part of each sub-system in order to avoid unnecessary complication of the Figures. Each sub-system comprises such a control-unit connected in the manner described in FIGS. 1 to 3. 
     FIG. 5 shows a situation as in FIG. 4, in which the destination terminal T D  is not &#34;free&#34;, but is communicating with a third terminal T E  associated with a further sub-system DS D . The connection is then established as follows First as described above with reference to FIG. 4, a connection is made between the sub-system DS A  and the operator sub-system DS B . Then the operator makes a connection both to the destination sub-system DS C  and to the terminal T E  associated with the sub-system DS D  communicating with that destination. For this purpose through a path in the T stage T B  of the peripheral module to which the operator is connected, the operator makes a connection to &#34;add-on circuit AO&#34;. From the add-on circuit AO connections are made to the destination sub-system DS C  and to the third sub-system DS D  both such connections being made indirectly through the source sub-system DS A . The connection of the operator to the destination sub-system DS C  is via T stage T B , the switching network SN B , the intersystem line IL BA , the switching network SN A , intersystem line IL AC , switching network SN C , T stage T C  to the destination terminal T D . The connection of the operator to the third sub-system DS D  is passed for a large part through the same route i.e. through T state T B , switching system SN B , intersystem line IL BA , switching network SN A , intersystem line IL AC , switching network SN C1 , switching network SN D , T stage T D , a third terminal T E . The operator then has the possibility to communicate simultaneously with the two terminals (T D  and T E ) and with terminal T S  separately. When the connection between terminals T D  and T E  is terminated then in switching system SN A  in source sub-system DS A  the path RUP (indicated by dashes) is connected further so that the connection between source terminal T S  and destination terminal T D  becomes established. It is also possible to attain this connection of source and destination in two phases i.e., by first in the switching system SN B  of the operator sub-system DS B  the path RPP (indicated by dashes) is made and only then the path RUP in switching system SN A . 
     The advantage of this manner of correction is that the final routing condition is as simple as possible. 
     It is obvious that the telecommunication system is suitable not only for transmitting call signals but also for carrying out also all kinds of data traffic.