Patent GB-1282156-A (GB)
Title: Switching system
IPC: G06F13/40
Filed: 1969-10-20
Abstract: 1282156 Switching systems INTERNATIONAL BUSINESS MACHINES CORP 20 Oct 1969 [13 Nov 1968] 51349/69 Heading H4K [Also in Division G4] A multiple-access business equipment, such as a computer, is made available to users over a group of m telephone exchange lines, the business equipment being able to give service to a lesser number of users than are connected over exchange lines, the exchange lines of those users waiting for an initial connection to the equipment, or preparing themselves for a further step in a dialogue with the equipment, being disconnected from the equipment but being held over the exchange. The charge made for use of the equipment can by this means be computed from the actual time of connection to the equipment which is distinguished from the total time connected over the exchange line. As shown, a group of m exchange lines, worked in the manner of a pabx group, gives access to business equipment 30. Each line of the group is terminated on line module 41 which automatically answers a call and signals a demand for connection to the business equipment by an output ISR1 to ISRm. Each exchange line has access over a line connect circuit 46 to an appearance on a switching network 48 which connects any available one of n data sets which provide inlets to the equipment 30. There are fewer data sets than exchange lines. If a data set is idle a circuit 43 produces an output DSI, a counter in this circuit being stepped forward each time a data set is seized and being stepped back each time an exchange line is released. If the counter reaches the total of all data sets, the output DSI is cancelled and all switching is inhibited until a data set falls idle. A priority connect circuit 44 determines whether service is given to calls newly established over exchange lines, or is given to lines established in a dialogue and asking for a further step in that dialogue after a period of being held to the exchange but disconnected from the equipment. A manual or programme-controlled switch determines which mode of priority control is in force. If a newly received call is not given immediate service a message is reverted to indicate that a delay will be encountered. The presence of a demand signal on one or more of the leads ISR1 to ISRm, together with a signal on DSI to indicate an available data set, assuming no competing demand of higher priority, starts a line scan circuit 42 which finds, and halts on, the demand condition or the first such condition. When halted, the scanner forwards one of the signals S 1 to Sm to the associated line connect circuit 46 which, by means of latching relays, switches the line through to the network 48 and connects a data set answer and ringing generator 45 which applies ringing on lead I to effect connection of a data set over the network and to detect such connection in order to disconnect ringing output I and signal the connection on lead DSA. The scanner 42 responds to connection with a signal on the appropriate lead of DSA1 to DSAm to cancel the demand signal ISR from the line module. The scanner position is gated to the business equipment interface 49 to identify the exchange line so that, when required, the line module may be controlled by selectively applied outputs SHC, SHR from system control 47. At this time the scanner may be reset to zero so that line searches always start from one end of the line group or, depending on the position of a manual switch, the scanner may start its scan from the point at which it was halted at the end of its preceding search. If the business equipment wishes to disconnect itself and place an exchange line in a hold condition, it generates one of the outputs SHC1 to SHCm from system control 47 to set up the appropriate line module accordingly. Reconnection to the business equipment is effected either at the instance of the equipment, which directs the production of the appropriate output SHR1 to SHRm from control 47, or by receipt of a signal from the user, both means resulting in a service request signal SSR from the line module. The request SSR is searched for by the scanner 42, either in preference to initial service requests ISR or after these have been satisfied as determined by the mode of priority connect circuit 44, assuming that a data set is idle. User release is detected in a line module and relays a release signal D.