GB1316343A - Tdm telecommunications systems - Google Patents

Abstract

1316343 Automatic exchange systems SIEMENS AG 28 Sept 1970 [30 Sept 1969] 46006/70 Heading H4K A TDM telecommunication link includes a first store at the transmitting end which reads in signals at a first rate corresponding to the frequency at which they are received, stores them in successive storage locations and reads them out at a second faster rate to provide pauses in transmission into which control signals are inserted, and at the receiving end the control signals are divided out and the remaining signals fed to a second retiming store from which they are read out at said first rate. In one embodiment shown the bits of a PCM TDM signal stream incoming at A si are alternately entered in a pair of bi-stables forming a store Sps under the control of a flip-flop FF1 at a frequency A fo. The bits stored are alternately read out under the control of a flip-flop FF2 at a slightly higher frequency A f1. After 24 bits comprising three 8 bit channels have been read out the flip-flop FF2 can be halted for one step providing a one bit space in the outgoing signal stream. A one bit control signal is inserted in this space via terminal As and an OR gate G 02 and the combined stream transmitted to the receiving station. Since there are 24 channels in a time frame an 8 bit control signal code can be transmitted with the bits distributed between groups of three channels. At the receiving station the control signals are divided out and a second retiming store operating in similar fashion to the store at the transmitting station re-distributes the signal stream to its original 24 frame format. A second embodiment with nine storage location selected cyclically in each store enables a 24 channel PCM TDM stream to be retimed in similar fashion to provide a 25 channel on which a complete 8 bit control signal code can be transmitted in a single time slot.