ATT System 25 Reference Manual

Figures
Figure 3-1.
Figure 3-2.
Figure 3-3.
Figure 3-4.
Figure 3-5.
Figure 3-6.
Figure 3-7.
Figure 3-8.
Figure 3-9.
Figure 3-10.
Figure 3-11.
Figure 3-12.
Figure 3-13.
Figure 3-14.
Figure 3-15.
Figure 3-16.
Figure 3-17.
Figure 3-18.
Figure 3-19.
Figure 3-20.
Figure 3-21.System 25 Digital Switch3-1
CPU/MEM (ZTN142) Circuitry3-3
TDM Bus Time Slot Generation (Not a Timing Diagram)                                                  3-6
TDM Bus—Three Cabinet System...

FUNCTIONAL DESCRIPTION
FUNCTIONAL DESCRIPTION
This section describes how the digital switch and the software of System 25 provide control and
switching.
Digital Switch
Figure 3-1 shows a block diagram of the System 25 digital switch. The basic switch hardware
consists of the following:
l Common Control
l Switching Network
—
—
—
COMMON
CONTROL
SWITCHING
NETWORK
Time Division Multiplex (TDM) Bus
Port Circuits
System Resource Circuits
CPU/MEM
TDM BUS
PORT
CIRCUITS
SERVICECIRCUITTONEDETECTORPOOLED
MODEM...

FUNCTIONAL DESCRIPTION
Common Control
The Common Control circuitry consists of a single ZTN142 CPU/MEM (Call Processing
Unit/Memory) circuit pack (CP).
CPU/MEM CP
The CPU/MEM runs the system feature code for the system and provides for the storage of
software associated with system operation. This CP is powered from the backplane by +5 and –5
volts. It also draws -48 volts from the backplane to drive the Emergency Transfer Unit. The CP,
shown in Figure 3-2, includes the following circuits:
l
l
l
l...

FUNCTIONAL DESCRIPTION
Figure 3-2. CPU/MEM (ZTN142) Circuitry
November 19953-3 

FUNCTIONAL DESCRIPTION
All uplink messages from the port circuits are checked for consistency and passed to the
Common Control. The controller is the distribution control point for all downlink control
messages. It continuously scans, over the TDM bus, the port circuit microprocessors for
sanity and activity. External RAM associated with this microprocessor stores control
channel information and port related information.
The controller consists of bus buffers and a Sanity and Control Interface (SAKI). It...

FUNCTIONAL DESCRIPTION
l Emergency Transfer Unit (ETU) Control
Removes -48 V dc power from the ETUs of the system when the system loses power
or a major system malfunction occurs.
l Bus Terminators
These resistors are required for proper operation of the TDM bus. The CPU/MEM
CP provides the proper termination for one end of the bus, and a plug-in TDM bus
termination circuit card (plugs into cabinet backplane) is used to terminate the other
end.For this reason, the CPU/MEM CP must always be located in...

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 packand data
the Time
and other
ports through the network control circuit.The system resource circuits provide tone
sources, receivers, detectors, and pooled...

FUNCTIONAL DESCRIPTION
l
lPhysical Characteristics
The TDM bus is an 8-bit bus that snakes continuously between cabinets in a
multicabinet system as shown in Figure 3-4. The total length is about 9 feet for a
three cabinet system.The bus is driven from any of the circuit packs in the cabinets.
Similarly, a signal on the bus can be received by any circuit pack.
Within a cabinet, the bus is printed on one side of the circuit pack carrier backplane
while the other side is solid ground.Ribbon cables are used...

FUNCTIONAL DESCRIPTION
TDM
BUS
TERMINATOR
CARD
TDM BUS
EXTENDER
CABLE
(CBC)
AC POWER
TO SINGLE
POINT GROUND
CABINET
ON/OFFSWITCH
3
AC POWER
# 6 AWGBUILDING
GROUND
WIRE
CABINET 2
AC POWER
#6 AWG
GROUND
WIRE
CABINET 1
COUPLED
BONDING
CONDUCTOR
Figure 3-4.TDM Bus - Three Cabinet System
3-8 

FUNCTIONAL DESCRIPTION
Port Circuits
The port circuit packs listed below provide the link between trunks and external equipment and the
TDM bus. Figure 3-5 shows the equipment types that can be connected to the digital switch by the
call processing and port circuit packs.
Analog Line (TN742/TN746)Loop Start Trunk (ZTN77)
ATL Line (ZTN79)MET Line (TN735)
Auxiliary Trunk (TN763)STARLAN Interface (ZTN84)
Data Line (TN726)Tie Trunk (TN760B)
DID Trunk (TN753)Tip Ring Line (ZTN78)
Ground Start Trunk (ZTN76)DS1...