Circuit arrangement for a telephone private branch exchange which consists of a main installation and at least one private branch exchange

摘要

In order to handle switching processes which relate to specific line features and/or for the purpose of central call data acquisition (which is provided in the context of determining charges), it is necessary to know that subscriber point (TU) of a private branch exchange (UA) for which a connection is to be produced in the outgoing or incoming direction. As such a performance feature it can be provided, for example, for switching systems having an illuminated digit display at the switching station that, in the cases in which the desired subscriber to a private branch exchange is not reached, his subscriber number is indicated at the switching station in the main installation when the so-called callback takes place, in the same manner as in the case of a subscriber point of the main installation (HA). The transmission of control data which is required in the context of the identification (which is to be carried out in this case) of the relevant subscriber point, and the transmission of the result data of the identification process take place via a specific line of the existing extension line harness (NAL). The said data are represented in coded form by AC voltage pulses at a frequency which is outside the voice band to be transmitted. For data protection, the data transmission is carried out at the same time via two permanently predetermined extension lines (NAL1 and NAL2). At the receiving end, the data transmitted in each transmission direction are supplied to a comparator (Vg) and are passed on to the subsequent functional units only if they correspond. If they are not identical, a repetition is initiated. IMAGE