Digital Switching Principles

Digital Switching

• The digital signals of several speech / datasamples are time multiplexed on a common media before being switched through the system.

• To connect any two subscribers, it is necessary to interconnect the time-slots of the two speech samples which may be on same or different PCM highways.

• The digitalised speech samples are switched in two modes, viz.,

• Time Switching and • Space Switching.

Space Switching

• In the space-switching mode, corresponding time-slots of I/C and O/G PCM highways are interconnected.

• A sample, in a given time-slot, TSi of an I/C HWY, say HWY1, is switched to same time-slot, TSi of an O/G HWY, SAY HWY2.

• Obviously there is no delay in switching of the sample from one highway to another highway since the sample transfer takes place in the same time-slot of the PCM frame.

Digital Time Switch

• A Digital Time Switch consists of two memories, viz., a speech or buffer memory to store the samples till destination time-slots arrive, and

• a control or connection or address memory to control the writing and reading of the samples in the buffer memory and directing them on to the appropriate time-slots.

• Time switch can operate in two modes, viz.,• I. Output associated control • ii. Input associated control

OUTPUT ASSOCIATED CONTROL SWITCH

INPUT ASSOCIATED CONTROL SWITCH

T S T SWITCH

T S T SWITCH STRUCTURE

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