AT&T AT&T manual Switching Network, TDM Bus Time Slot Generation Not a Timing Diagram

Switching Network

System 25 uses distributed processing techniques to provide switched voice and data services. The switch operates at 64 Kbps. The switching network consists of the following:

●Time Division Multiplex (TDM) bus

●Port Circuits

●System Resource Circuits.

The TDM bus connects the intelligent ports to the Common Control circuit packs and other ports through the network control circuit. The system resource circuits provide tone sources, receivers, detectors, a n d p o o l e d m o d e m s . T h e i n t e l l i g e n t p o r t s c o n n e c t e x t e r n a l communications facilities to the TDM bus.

TDM BUS

The TDM bus consists of two groups of eight signal leads and five control leads, each with matching grounds. The port circuit packs place digitized voice [pulse code modulated (PCM)] signals on the bus.

The bus operates at 2.048 MHz. The framing pulse rate is 8 kHz. This provides 256 time slots (0-255) on the bus. The time slots are 488 ns wide. Time slots are generated as shown in Figure 3-4.The first five time slots are used for communications between the Common Control, the intelligent port, and resource circuit packs.

SYSTEM FRAME

8 KHZ

				( 125		MICROSECONDS)
			488	NANOSECONDS
							— — — — — — — — —		0
TIME SLOTS O	1	2		4		5		255
					256	TIME SLOTS

Figure 3-4. TDM Bus Time Slot Generation (Not A Timing Diagram)

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