The Post Office

Donald William Smith

Arthur Robin Potter

John H Hardy

Robert E Barrett

Garth I Riley

John Hovell

Anthony R Allwood

Ian W Lowrie

A digital switching device of the stored program type operating under the control of a central control unit has a first stage which multiplexes digital signals from a plurality of line units and separates data signals from signalling information. The data signals are fed to an input time switching stage. The input time switching stage operates under the control of the central control unit to transmit signals from an input port in a particular time slot on a highway to an output time switching stage. The output time switching stage transmits the data signals to the first stage which combines them with signalling information and after demultiplexing transmits them to appropriate ports.

Switching of digital signals

A telephone system is disclosed in which local groups of customers each have a respective concentrator. The concentrators are connected to two main switching centers by pulse code modulation highways. Four highways from each of eight concentrators are shown and each highway from a concentrator is terminated on a different group control, there are two group controls in each main switching center. Each concentrator contains a line unit, a switching network, a signalling unit, auxiliary units, a pulse code modulation multiplexor and control logic. The line unit detects the customer calling condition; the switching network is a two stage analogue crosspoint switch connected from customers' lines to the signalling unit; the signalling unit provides an analogue/digital interface; the auxiliary units provide special facilities such as coin fee checking; the pulse code modulation multiplexor passes data to and from the main switching centers; and the control logic controls the operation of the concentrator in accordance with instructions received from a main switching center. The main switching centers instruct the concentrators on the allocation of pcm channels to customers and the interconnection of two customers is performed by an interconnection of channels within a switching center. The switching network of each concentrator is made up of a number of sections and information is sent on each highway as to which sections are being addressed on the other highways of the concentrator. The system includes an arrangement to avoid setting up the same connection at once on two highways.

Improved digital telephone and switching system employing time division

A digital telephone system is disclosed in which local groups of telephone lines are connected to respective concentrators which are themselves connected to switching centers by pulse code modulation highways. Data is transmitted on the highways as a succession of superframes where one superframe equals four multiframes, one multiframe equals 16 frames, one frame equals 30 channels and one channel equals eight digits. Channels 0 and 16 are used for signalling within the system and the remaining channels are used for data transmission between the telephone lines. The interpretation of channels 0 and 16 is determined by the particular frame and multiframe in which they occur. Each telephone line is identified by a combination of three channels representing a particular section of a concentrator, a particular block in the section, and a particular address in the block. Each concentrator has four sections and four highways. On each highway, the sections are scanned in turn, each for a period of one superframe. When all four sections have been scanned there is a one superframe period with no scan before the sections are scanned again on that highway. The superframe start times are mutually staggered by 16 frames on the four highways. Each highway transmits the relative superframe timings of the other three highways of the associated concentrator and this information is processed at the switching centers and used to control the superframe start time of the highway transmitting the information. The complement of the correct degree of stagger is added to the actual degree of stagger and the result compared with other totals similarly derived.

Digital telephone and switching system employing time division multiplex

Growing community of inventors

Ipswich, United Kingdom

Donald William Smith