ATT System 25 Reference Manual

							HARDWARE DESCRIPTION
HARDWARE DESCRIPTION
This Section provides descriptions of System 25 hardware components and their functions.
The hardware is covered under the following major headings:
l System Cabinets:Includes circuit pack (CP) carriers, power supplies, wiring, and
cooling equipment.
l Circuit Packs: Includes detailed information on CPs.
l Terminal Equipment:Equipment that can be connected to voice or data station
ports.
l Peripheral Equipment: Equipment that can be connected to the CPU/MEM CP.
l Auxiliary Equipment: Service- and feature-related supporting equipment.
l Connectivity: Equipment and arrangements for interconnecting the various elements
of System 25 hardware.
Note:Equipment that is directly associated with a specific feature or service
covered in Section 2 is also described there; such equipment is noted in this
Hardware Description section, with a reference to the appropriate heading in
Section 2.
All system hardware, except Cabinet 1 equipped with a CPU/MEM, Service Circuit, and
associated cables, is optional.
A listing of Product Element Codes (PECs), Apparatus Codes, and Comcodes is provided in
Section 7, “Parts Information.”
System Cabinets (J58901A1 L4)
The system can consist of one, two, or three cabinets (Figure 4-1). Each cabinet contains its
own power supply and cooling system.A CP carrier frame is integrated into each cabinet.
Depending on the circuit pack complement, the cabinet/circuit pack configuration is as
follows:
l Cabinet 1 (always required)—Contains the CPU/MEM CP and the Service Circuit of
the system and can also contain up to ten port CPs.
l Cabinet 2 or 3 (optional)—Provides mounting for up to 12 port CPs each.
The CPs receive power, control signals, and data via the backplane bus of the carrier and
associated 25-pair connector interfaces.In multiple cabinet systems, the backplane buses
are linked with a bus extender cable (J58901A4 L3).
4-1 
						

							HARDWARE DESCRIPTION
The cabinets have a brown front cover with beige top and sides. The front cover has a
system identification stripe across the top.The top has four indentations to facilitate the
stacking of cabinets.
Each cabinet is constructed of sheet metal and is 13 inches high, 17 inches wide, and 21
inches deep and weighs about 75 pounds fully loaded.A 3-cabinet system occupies a
vertical space of about 40 inches.It is recommended that the cabinets be placed on a desk-
or table-top. They must not be placed on a floor where cleaning solutions and dirt can get
into them.Refer to Section 6,“Environmental Requirements” for equipment area
considerations and associated floor plan recommendations.
The front cover of the cabinet is secured by four screws. These screws must be loosened
slightly before the cover can be removed.When the cover is removed, access is provided to
the CPs, a replaceable air filter mounted just under the CP carrier frame, and two cooling
fans. The cooling fans are mounted on an assembly that, when unscrewed, provides access
to the power supply. Air intake is at the bottom of the cabinet and exhaust is vented at the
left side of the front cover.
Each cabinet has its own power supply mounted to the left of the CP carrier. The power
supply is 3 inches wide and weighs about 9 pounds.Voltage and current supplied to the
carrier are: +5 V dc at 35A, -5 V dc at 3A, -48 V dc at 3A, and 90 V ac at 0.16A.
On the front of the supply is a green Light-Emitting Diode (LED) that, when lighted, indicates
that the +5 V dc is available and within limits. The LED can be viewed through the slotted
area on the front cover, and is just behind the fan located at the top left edge of the cabinet.
Mounted on the back of the cabinet (Figure 4-2) is the aluminum grounding block with four
terminating positions,an ac input power receptacle, a power On/Off switch [(1)=ON,
(0)=OFF] and twelve 25-pair connectors.The ground block is connected to dc ground on the
carrier backplane at a location near the power supply. The 25-pair connectors provide an
interface between cross-connect wiring and the CPs immediately behind each connector.
Two slots are provided in the rear cover just above the 25-pair connectors for the Time
Division Multiplex (TDM) bus extender cable.The TDM cable is used to connect 2- or 3-
cabinet systems in a daisy-chain configuration and provides control and data signals
between cabinets. The Cabinet 1 ground block is connected to the single-point ground of
the system using 6 AWG wire.Separate 6 AWG wires are then connected from the Cabinet
1 ground block to Cabinets 2 and 3 ground blocks.The Cabinet 1 ground block is also
connected to the Coupled Bonding Conductor.An information label is provided across the
top portion of the rear panel on each cabinet.The label provides cabinet identification, input
electrical requirements, caution and warning notes, and FCC, CSA, and UL labels.
4-2 
						

							HARDWARE DESCRIPTION
—
—
—CABINET 3
(12 PORT CIRCUIT PACKS)
CABINET 2
(12 PORT CIRCUIT PACKS)
CABINET 1
(CONTROL AND SERVICE
CIRCUITS; 10 PORT
CIRCUIT PACKS)
Figure 4-1.
System 25 Cabinets (J58901A)—3-Cabinet System
4-3 
						

							HARDWARE DESCRIPTION
CAUTION & WARNINGGROUNDING
LABELSFCC LABELBLOCK
SYSTEM 25
VOLTS AC
J58901A
AMPS
HZ
25-PAIR
CONNECTORSINPUTON/OFF
AC POWERSWITCH
RECEPTACLE
Figure 4-2.
System Cabinet (J58901A)—Rear View
Cabinet 1 (Control and Port Circuits)
Cabinet 1 (Figure 4-3) is always required.It provides mounting space for 12 CPs and can
support a small telecommunications system (for example, 50 to 60 stations and 10 to 15
trunks.)
Cabinet 1 contains the CPU/MEM CP and the Service Circuit, which must be mounted in CP
slots 1 and 2, respectively. Slots 3 through 12 (ten total) provide mounting for the various
port CPs that can be used. Any port CP can be mounted in any of these ten slots.
The Tone Detector and Pooled Modem CPs (referred to as System Resource CPs) can also
be mounted in the port CP slots.Circuit packs are described in this Section under the
heading “Circuit Packs”.
Cabinets 2 and 3 (Port Circuits)
Cabinet 2 and Cabinet 3 (Figure 4-3) can be added to provide mounting space for additional
port CPs (12 maximum each) required for larger systems. The Tone Detector and Pooled
Modem CPs can also be mounted in these cabinets.These cabinets are simply stacked on
top of Cabinet 1.Table 4-A summarizes port CP capacity of 1-, 2-, or 3-cabinet systems.
4-4 
						

							HARDWARE DESCRIPTION
POWER SUPPLY
1
23
45
67
89101112
PORT CIRCUITS
POWER SUPPLY
CIRCUIT PACK SLOTS
CPU/MEMSERVICE CIRCUIT
CABINET 1—MOUNTING FOR CONTROL & PORT CIRCUIT PACKS
CIRCUIT PACK SLOTS
12
34
5
6789101112
PORT CIRCUITS
CABINET 2 OR 3—MOUNTING FOR PORT CIRCUIT PACKS
NOTES:
1.
2.
3.4.
5.
6.
REFER TO TECHNICAL SPECIFICATIONS, SECTION 5 FOR CIRCUIT PACK UNIT LOAD INFORMATION.DIVIDE THE TOTAL NUMBER OF VOICE TERMINAL AND TRUNK CIRCUIT PACKS BETWEEN THE CABINETS
USED.
MOUNT VOICE TERMINAL CIRCUIT PACKS FROM THE RIGHT, TRUNK CIRCUIT PACKS FROM THE LEFT.
COMMON CONTROL CIRCUIT PACK (MUST BE MOUNTED IN SLOT 1 OF CABINET 1)
l CPU/MEM (ZTN142)
SYSTEM RESOURCE CIRCUIT PACKS (SERVICE CIRCUIT MUST BE MOUNTED IN SLOT 2 OF CABINET 1.POOLED MODEM AND TONE DETECTOR MAY BE MOUNTED IN ANY PORT CIRCUIT SLOT.)
l SERVICE CIRCUIT (ZTN131)
l TONE DETECTOR (TN7488)
l POOLED MODEM (TN758) (MAXIMUM 2 PER CABINET)
PORT CIRCUIT PACKS (UNIVERSAL PORT CIRCUIT PACKS CAN BE MOUNTED IN ANY AVAILABLE PORTSLOT.)
l TIP RING LINE (ZTN78)
l ATL LINE (ZTN79)
l MET LINE (TN735)
l ANALOG LINE (TN742)
l AUXILIARY TRUNK (TN763)
l STARLAN INTERFACE (ZTN84)
l DATA LINE (TN726)
l GROUND START TRUNK (ZTN76)
l LOOP START TRUNK (ZTN77)
l DID TRUNK (TN753)
l TIE TRUNK (TN760B)
l DS1 INTERFACE (TN767)
Figure 4-3. System Circuit Pack Configurations
November 19954-5 
						

							HARDWARE DESCRIPTION
Cabinet Address Plug
An address plug is provided on the middle of the backplane of each cabinet (accessible after
removing the top rear cover) and is used to designate the cabinet number to the software. When
address plug is plugged into the designated area at CP slot 5, the cabinet is identified as Cabinet 1
at slot 6 as Cabinet 2, and at slot 7 as Cabinet 3.
*
†
Table 4-A. Total Port Circuit Packs Per System
NUMBERPORTTOTAL PORT
OFCABINETCIRCUIT
CIRCUIT
CABINETSNUMBER *
PACKSPACKS †
1Cabinet 11010
2Cabinet 11022
Cabinet 212
3Cabinet 11034
Cabinet 212
Cabinet 312
Cabinet 1 (always required)—Provides mounting for CPU/MEM, Service Circuit, and
Port CPs including Tone Detectors and Pooled Modems.
Cabinet 2 and 3 (optional)—Provides mounting for Port CPs including Tone Detectors
and Pooled Modems.
The Number of Ports per CP is specified in the CP descriptions.
4-6
November 1995 
						

							HARDWARE DESCRIPTION
Circuit Packs
This part describes required and optional System 25 Circuit Packs (CPs) and their compatibility and
features. Required CPs are the CPU/MEM and the Service Circuit. Optional CPs are the Station
Port CPs, Trunk Port CPs, Pooled Modems, and Tone Detectors; the latter two CPs, plus the
Service Circuit, are also classified as System Resources. Table 4-B lists the CPs of System 25. For
more detailed functional descriptions of the CPs, refer to Section 3 of this manual.
Table 4-B. System Circuit Packs
CIRCUIT
NUMBER
CIRCUIT PACKTITLEPACKOF
TYPE
PORTS
TN726Data LineP8
TN735MET LineP4
TN742Analog LineP8
TN746BAnalog Line
P
16
TN747BCO TrunkP8
TN748B
Tone Detector †R4
TN753
DID TrunkP8
TN758
Pooled Modem †R2
TN760B
Tie TrunkP4
TN762B
Hybrid LineP8
TN763Auxiliary TrunkP4
TN767DS1 InterfaceP24
ZTN76Ground Start TrunkP8
ZTN77Loop Start TrunkP8
ZTN78Tip Ring LineP8
ZTN79ATL LineP8
ZTN142CPU/MEMC4
ZTN84STARLAN Interface
P4
ZTN131Service Circuit ClockR4
* P = Port, C = Control, R = System Resource.
† System Resource Circuits (Tone Detector, Clock Pooled Modem, Service Circuit) ports
are internal to the system. These ports are not connected to external equipment via 25-
pair connectors.
November 19954-7 
						

							HARDWARE DESCRIPTION
Required Circuit Packs
The following CPs are provided with all Release 3 systems and must be mounted in Cabinet 1:
l ZTN142 CPU/MEM (Call Processing Unit/Memory)
The ZTN142 (one per system) provides a central processing unit, Random-Access Memory
(RAM) (memory) for call and feature processing, interrupt controller, programmable timers,
real time clock, status display, processor bus interface, and four interface ports. It also
provides Read-Only Memory (ROM) for translations and a 1200-baud answer-only modem
for Remote Initialization and Maintenance Service (RIMS) access. The five interface ports
provide the following interfaces:
— Port 1 - System Administration Terminal (SAT)
— Port 2 - Station Message Detail Recording (SMDR) equipment
— Port 3 - Digital Tape Unit
— Port 4 - Reserved
— Port 5 - RIMS
The CPU/MEM also provides -48 VDC control on ports 7 and 8 for Emergency Transfer
Units.
The CPU/MEM CP must be mounted in slot 1 of Cabinet 1.
l ZTN131 Service Circuit
The ZTN131 (one per system) provides four touch-tone receivers, generates all system
tones, and supplies the system clocks. The ZTN131 can support up to 75 voice terminal
stations.
The ZTN131 synchronizes the System 25 to a master DS1 data stream, monitoring the
reference clock, and maintaining a stratum 4 clock for synchronizing transmission on all
DS1 ports.
The Service Circuit CP must be mounted in slot 2 of Cabinet 1.
4-8November 1995 
						

							HARDWARE DESCRIPTION
Optional Circuit Packs
The following CPS are optional and can be mounted in any slot not occupied by the required CPS.
Station Port Circuit Packs
l TN726 Data Line
Provides eight ports for Asynchronous Data Units (ADUs). Used for in-building service
within 2000 feet of the system cabinets. Data speeds from 300 bps to 19.2 Kbps are
supported. Service beyond 2000 feet at less than 19.2 Kbps is supported; see Section 5
“Technical Specifications.”Extends a serial communications link from the system to data
equipment over standard station wiring.
l TN735 MET Line
Provides four ports for Multibutton Electronic Telephone (MET) sets. Used for in-building
service within 1000 feet of the system cabinets.
l TN742/TN746 Analog Line
Provides eight ports (16 ports for TN746) for single-line voice terminals with or without non-
neon message waiting lamps. Also supports Off Premises Stations (OPS) and out-of-
building service. Auxiliary equipment interfaces are also supported. Used for service within
24,000 feet of the system cabinets. Five voice terminals can be bridged onto each port.
Only two terminals can be off-hook simultaneously on each port; otherwise, transmission
can be degraded.
Note: The Off-Premises Stations
l ZTN78 Tip Ring Line
Provides eight ports for single-line sets
Used for in-building nonbridged voice
cabinets.
Note: Equipment connected for
following requirements:
— AC impedance: 600 ohmsmust be FCC registered.
with or without non-neon message waiting lamps.
terminal service within 2000 feet of the system
ZTN78 Tip Ring Line CP port must meet the
— DC current: Less than 30 ma at 48 volts
— Ringer Equivalence Number (REN): Less than 1.15 (set plus adjuncts).
The ZTN78 CP ports can also be used for interface with the AT&T VOICE
Message System (VMS).
l ZTN79 ATL LinePOWER Voice
November 19954-9 
						

							HARDWARE DESCRIPTION
Provides eight ports for MERLIN® Communications System voice terminals and ATL
cordless telephones. Used for service within 2000 feet of the system cabinets; ATL cordless
telephones and corded multiline voice terminals more than 1000 feet from the system
cabinet require local power. Off-premises extensions are not supported, Out-of-Building
stations require In-Range Out-of-Building (IROB) units.
l ZTN84 STARLAN Interface
Provides one physical port for interface with AT&T STARLAN NETWORKs (Release 2 of
STARLAN only). It supports four simultaneous data endpoints connected to the STARLAN
NETWORK. The Network Extension Unit must be colocated with the System 25 cabinets.
4-10November 1995