Patent GB-1374635-A (GB)
Title: Data processing apparatus
IPC: H04Q3/54
Filed: 1972-08-09
Abstract: 1374635 Automatic exchange systems GTE INTERNATIONAL Inc 9 Aug 1972 [20 March 1972] 13031/72 Heading H4K Data processing apparatus comprises a plurality of functionally different units coupled to a data bus to which all possible data codes transmittable to the units are transmitted in cyclic succession, each unit including a store for a code and a comparator which upon detection of coincidence between a stored code and a code on the bus produces a response, which if that unit determines that another unit is to receive the code, actuates means to allot such further unit to receive the code. As shown a PABX includes a number of register units RGU, a number of local connection units LLU, a number of exchange line connection units ELU, and a number of ring back connection units RBU. Among the units of each type, one to be used next is allotted by a corresponding alloter RA, LA, EA or RBA respectively. Each register unit, local connection unit and ring back unit includes separate stores for calling and called numbers each with an associated comparator, while each exchange line unit has only one store and associated comparator, the latter store holding the identity of the extension (i.e. calling subscriber for outgoing calls and called subscriber for incoming calls). The system initially provides for up to 100 extensions. A master scanner generates the subscriber addresses in sequence on a data bus E1D, a class of service translator COS adds the class of service data on a bus CSD and a line state discriminator LSD synchronously supplied with the states of the subscriber lines by a line scanner LG adds line state data (this can be "busy", "free" or "parked") on a highway LSH. A highway PGD is provided via which the units can control a sequencer SQ and thus the master scanner to effect transmission of data to other units. A "P" wire connected to the units is associated with the highways and is marked busy by any unit having access to the highways to ensure that only one unit at a time is actively controlling transmission on highway PGD. Each unit requiring to use the highway PGD applies to a one only allotter OA which returns a "GO" signal to the unit next to use the highway. Each unit controls a separate switch arrangement which provides a continuous speech connection to an extension or in the case of a local connection unit, to two extensions to provide a complete local connection. A local call for example is dealt with as follows. When a calling subscriber identity is generated the line state discriminator detects the off hook condition and transmits this on the line state highway LSH. In addition if it detects that this is a new call by comparison with the previous line state it signals over a line LST to the sequencer which stops the clock driving the master scanner. The extension identity is thus staticized on the highway EID. The line discriminator also applies via a line ACl, a strapping field STF and a lead ST 1 to the register allotter RA, which causes an idle register unit to store the extension identity in its calling store After a delay sufficient to allow for this registration the sequencer allows the master scanner to continue scanning. Each time that extension is scanned the comparator associated with the calling store of that register responds gating the line state into the register unit to compile the dialled number. Three digits are normally dialled the first indicating the type of call, e.g. internal and the other two the identity of the called subscriber. If the first digit is a 2 indicating a local call the remaining digits are entered in the called number store. The register unit then applies to the one only allotter OA for access to the highway PGD and after receiving a "GO" signal therefrom and upon detection of the next occurrence of the calling extension identity on the highway EID transmits a "stop 1" signal on highway PGD causing this address to again be staticized on highway EID by stopping the master scanner. The register unit then applies via line AC2, strapping field STF and line ST2 to a local line allotter LA which causes a local line unit to be selected and the calling extension identity fed in its calling store. After a short delay the sequencer allows the scanning to continue until the called identity is transmitted on the highway EID. When this occurs the called store comparator in the register unit involved responds transmitting a "stop 2" signal on highway PGD staticizing the called extension identity on the highway and causing it to be entered in the called store in the local line unit LLU. The line unit sets up the call and continues its supervision, the register unit clears and releases and after a further delay determined in the sequencer scanning continues. If the first digit dialled is a "9" indicating an outgoing call and the caller has the necessary class of service, connection is effected to an exchange line unit, the calling extension identity is transferred under a scan halted by a "stop 1" signal in a manner similar to that above, and the register unit releases following a second scan in which no "stop 2" signal is produced. Ring back units RBU are provided such that an executive extension attempting to make a call to another extension which is busy may by dialling an extra (4th) digit get the called extension identity and the executive extension identity transferred for temporary storage in a ring lock unit which monitors the extensions for busy condition and transfer the stored identities to a local connection unit when the connection can be set up, both transfer taking place in a "stop 1", "stop 2" sequence along lines similar to that above. During a main exchange call an extension may by earthing his line loop cause the exchange line to be held, a register unit to be selected, the subscriber identity to be entered therein, the identity of another extension dialled by the first extension to be stored, a local connection unit to be selected and the two extensions identities transferred thereto to enable interim conversation between the extensions and depending on the whether the first extension re-earths its line pair or clears down to reselect the same exchange line unit and transfer the first or second extension identity thereto to connect that extension to the exchange line. Incoming calls are initially dealt with by an operator, the line being automatically looped and an indicator actuated at the operator positioned. The called extension is entered in an operators register. The incoming caller can camp on a busy extension and be automatically connected thereto by the exchange line unit when the extension becomes free. The speech path switches by which the units can connect to the extension are relay contact trees (Fig. 7, not shown), the relays controlling the contacts effecting via further contacts the comparisons and functioning as the stores.