Instruction manual

FUNCTIONAL DESCRIPTION
Switching Network
System 25 uses distributed processing techniques to provide switched voice
services.
The switch operates at 64 Kbps.
The switching network consists of
Division Multiplex (TDM) bus, the Port Circuits and the System Resource Circuits.
The TDM bus connects the intelligent ports to the Common Control circuit pack
and data
the Time
and other
ports through the network control circuit.
The system resource circuits provide tone
sources, receivers, detectors, and pooled modems.
The intelligent ports connect external
communications facilities to the TDM bus.
TDM Bus
The TDM bus consists of two groups
matching grounds. The port circuit
(PCM)] signals on the bus.
of eight signal leads and five control leads, each with
packs place digitized voice [pulse code modulated
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 3-3.
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
—————————
SYSTEM CLOCK
2.048 MHZ
TIME SLOTS O
1 2
3
4
5
255 0
256 TIME SLOTS
Figure 3-3.
TDM Bus Time Slot Generation (Not A Timing Diagram)
Two time slots are required for each 2-party conversation.
Each party transmits (talks) on
one time slot and receives (listens) on another.
Only five parties are allowed in a conference.
During a conference connection, each member of the conference transmits on an individual
time slot while receiving on as many as four other time slots. The actual switch capacity is
115 simultaneous 2-party conversations.
Table 3-A shows the allocation of the 256 time slots. Five are used for system control, 17
for tones, 232 for call processing, and two are not used.
3-6