ES378169A1 - Improvements in or relating to telecommunication system - Google Patents

Abstract

A time division multiplex, pulse code modulation telecommunication system adapted to transmit both data and speech employs timeassigned speech interpolation for speech transmission between switching centres during heavy traffic conditions. A system is outlined in which each multiplex highway employs 32 time slots of which 30 are used for speech or data and 2 are used for TAS1 order-wire signals. Each slot comprises 8 bits and the 2 order-wire slots together transmit a 16-bit code. In a group of 4 successive cycles, two such codes are used for TASI control, one is used for synchronization and the last for normal order-wire control. During heavy traffic periods TAS1 techniques come into operation. When a speech channel is silient between speech bursts, are all zero PCM code is sent and after 4 successive cycles the speech path is broken and re-established when speech again commences. Data blocks are headed by and separated by an all one codes to avoid breaking down of the path during data transmission. During idle traffic periods the all zero codes are omitted. The switching network at each switching centre is of space-time space format and includes a plurality of junctor circuits, each of which can connect any time slot of any input channel to any time slot of any output channel. Each junctor includes first and second cyclic stores each having a storage location for each time slot, and a random access store. The locations of the first and second cyclic stores are individually associated with incoming and outgoing calls respectively. In two alternative embodiments there is a location in the random access store for each time slot. Each storage cell in one cyclic store by its time position gives the location of a random access storage cell to receive a PCM sample and the corresponding location in the other cyclic store stores the location of the random access storage cell which contains the PCM sample to be sent out to a called time at that instant. In a third embodiment the number of storage locations in the random access store equals the maximum number of simultaneous calls and both cyclic stores store an address of a random access storage cell. It is stated that PCM codes may be transmitted through exchanges not having store and forward message equipment by the use of the all ones code as a pulse stuffing device.