A telephone switching network for digital speech transmission is characterized in that a dialing information input by an originating subscriber into an originating switching center is employed to complete a virtual connection departing from the originating switching center and proceeding over one or more tandem switching centers, as required, and extending up to a destination switching center to which an appertaining destination subscriber is connected. A speech information to be transmitted is subdivided into speech segments or phrases and a respective phrase, in the form of an information block having a preceding destination identifier sequence which contains data concerning virtual partial connections to be respectively traversed and an end identifier at the end of the phrase and indicating the end of the phrase, is transmitted in proper time between the subscribers via real partial connections respectively built-up for an appertaining, current phrase between two switching centers. The virtual connection is disconnected after termination of the call.

A time assignment speech interpolation system is disclosed utilizing time-shared common control processing circuits. Speech signals from a plurality of trunks are interpolated on a lesser plurality of transmission channels by connecting trunks only during active periods. In order to accommodate transmission channels of varying delay times (e.g., cable and satellite channels), receiving terminal switching operations are delayed for a time corresponding to the transmission delay of the corresponding channel. This is implemented by common control digital delay time-out for each new connection.

A time assignment speech interpolation system has a random access memory which provides both a fixed and a variable delay between an input speech channel and a transmission facility. Digital samples of the signal detected on an input speech channel are stored for a fixed time in a portion of the memory in order to provide time for switching without clipping and for generation of a channel identifying symbol. If a transmission facility is available, the sample is read out of memory after the fixed delay and reconstituted into an analog signal which is transmitted on the available facility. If no transmission facility is available, the samples are read out of memory after the fixed delay and written into another portion of memory which stores them for variable times until a transmission facility is available. In one embodiment, the portions of the memory assigned to providing variable delay are paired. Starting addresses are at the two extremes of memory locations in a pair, and successive memory locations extend toward the other extreme starting address. In another embodiment, the memory assigned to providing variable delay is segmented. As one segment is filled, it is linked to another available segment. In this embodiment, silence purging logic may also be provided which determines whether any of the samples stored in particular segments represent silence or pauses in the stored speech. If they do, these segments are then classified as available.

A time assignment speech interpolation system has a random access memory which provides both a fixed and a variable delay between an input speech channel and a transmission facility. Digital samples of the signal detected on an input speech channel are stored for a fixed time in a portion of the memory in order to provide time for switching without clipping and for generation of a channel identifying symbol. If a transmission facility is available, the sample is read out of memory after the fixed delay and reconstituted into an analog signal which is transmitted on the available facility. If no transmission facility is available, the samples are read out of memory after the fixed delay and written into another portion of memory which stores them for variable times until a transmission facility is available. The portions of the memory assigned to providing variable delay are paired. Starting addresses are at the two extremes of memory locations in a pair, and successive memory locations extend toward the other extreme starting address.

In a time assignment speech interpolation system, a fixed delay between the input speech channel and the transmission facility provides time to generate and transmit a symbol representing the speech channel to which the transmission facility has been assigned. At the remote location, a fixed delay between the transmission facility and the output speech channel provides time in which to detect the symbol and perform the necessary switching.