Patent GB-1367442-A (GB)
Title: Telephone exchange with multiparty communication facilities
IPC: H04Q3/545
Filed: 1973-02-15
Abstract: 1367442 Automatic exchange systems INTERNATIONAL BUSINESS MACHINES CORP 15 Feb 1973 [29 Feb 1972] 7411/73 Heading H4K A stored-program controlled exchange having multiparty communication facilities as defined below comprises data storage apparatus arranged in operation to store a transaction table comprising pairs of entries, each different pair identifying the pairs of two connected or posted for connection to a different junctor and each entry contains information identifying the line to which the entry relates, status information indicating whether the connection is made or posted, and, in the case of a line for which connection is made, chaining information defining whether the line is posted for connection to another junctor, the system being responsive to a signal generated on a line in multiparty communication to disconnect the line from a junctor and in accordance with the chaining information to connect the line to another junctor. A line X is defined as being in multiparty communication, if, when connected to another line Y, a connection path has been prepared between X and at least one further line Z. In such a situation line X is said to be posted for connection to a junctor to which line Z is actually connected. General (Fig. 1).-The application is to a PABX having cross-point switching arrays 2 controlled from a central processing unit 4 via a marker 10. Line state test circuitry 1 is controlled via line state test control circuits 9 and all connections are established via junctors 3 having access to servicing circuits 11 including ringing circuits, lone generating circuits, operators consoles, call counters &c. All such circuitry may be known and path finding &c. may take place in known manner. Particular description.-The exchange is characterized by the arrangement of information relating to multiparty communication in the control unit store 5 and its operation in respect thereof. There is provided a line table 7, Fig. 2b, and a transaction table 8, Fig. 2c, the entries therein relating to the situation shown in Fig. 2a. The line table 7 includes a field 32 which indicates the junctors to which lines are connected, each junctor having a conceptualized high (h) and low (b) side. The transaction table 8 contains two entries for each junctor i.e. for its high and low sides respectively, and the entries are divided into three fields. Field 33 indicates a line connected or posted for connection to the junctor, and field 34 indicates the line's status using the following code a.c.t.-the line is actually connected to the junctor; m.g. -the line is a posted line and the line connected to the other side of the junctor is a stacked external line; a.s.-the line is a posted line and the line connected to the other side of the junctor is an internal line which is camping on; d.a.r.-the line is a posted line, and the line connected to the other side of the junctor was previously in communication with the identified line and is now stacked. Field 35 is a chaining field and indicates the type of multiparty communication in which a line is participating. Bit position d refers to a reversible transfer dual call. This occurs because an internal line X already connected to an internal or external line Y can accept a call from another internal line Z while keeping the possibility of re-connection to Y by means of a return signal. If X is reconnected to Y the line can be re-connected to Z by a return signal. Position g refers to a stacked external line. The operator acts to reserve a link between a calling external line, e.g. T and a line X already connected to a line Y. X, when warned by the operator, can either go on-hook which breaks the connection with Y making X a normal called line or by dialling an accept signal, go into a reversible dual call condition. Bit position a refers to a camping on line: i.e. a user for internal line Z which calls an internal line X already connected to another line Y can dial a camp-on signal which reserves a path between Z and X and warns X. The bit positions d, g, a are given a bit 1 if the line in field 33 is connected to the respective junctor and is posted to another junctor for the condition assigned to the bit position. Hence it can be seen from tables 2b, 2c that line X is posted for connection to junctor J2 in a camp-on situation. The control unit 4 acts in response to three different signals, i.e. an accept signal, a return signal and a hang-up signal with reference to the stored tables 7, 8 according to a program the steps of which are outlined with reference to Figs. 3a-8b (not shown) representing different connection situations between a group of six lines. Four procedures are outlined-a call acceptance procedure, a return signal procedure, a hang-up by standing-by line procedure, and a hang-up by a line in multiparty communication procedure, which will not be described here, the procedures being a fairly direct result of the manner in which the tables 7 and 8 are arranged. The system may be modified by arranging for stacks of different priority, e.g. first and second priority. These would then be considered as different kinds of posting and would be represented by different bits in field 35 of the transaction table.