ATT System 25 Maintenance Manual

							SYSTEM HARDWARE
The USART interfaces the DUCKs serial data stream to the conversion
microprocessor. The USART can be programmed by the microprocessor to
operate synchronously or asynchronously. The USART also performs the
following tasks for the port circuit microprocessor:
l
l
l
lAppends start and stop bits to parallel data received from the
microprocessor in the asynchronous mode
Converts serial data received from the DUCK to parallel data
Buffers data in both directions
Detects and generates break characters.
The DSP provides modem emulation. It interfaces the port circuit signal and
the remote modem. The microprocessor directs the DSP to execute one of
many programs. The DSP produces data, carrier detection, and timing
information for the port circuit microprocessor.
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							SYSTEM SOFTWARE
General
The System software consists of switched services, administrative, and
maintenance software. This software runs on top of the real-time operating
system software.
Switched Services Software
The switched services software provides voice and data call processing.
This software resides in the Call Processor and Memory circuit packs
(collectively referred to as the Common Control circuitry) and in the 8-bit on-
board microprocessors located in the port and service circuits.
The switched services software uses the operating system to provide a
process based, message passing, execution environment. The operating
system scheduler provides scheduling for the software according to process
priority.
Administrative Software
The administrative software provides the control for system rearrangement
and change using the System Administration Terminal (SAT). This software
resides in the Memory circuit pack and performs the following functions:
l
l
lOrganizes the translation data for administrable entities in the system in
a form that can be viewed and changed at the SAT.
Tests entered data for consistency with data previously entered in order
to avoid such errors as the assignment of the same extension number to
two voice terminals. An erroneous or inconsistent data entry is
disallowed and an error message is provided.
Causes the translation data to be downloaded, on command, to an
optional Digital Tape Unit (DTU).
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							SYSTEM SOFTWARE
Maintenance Software
The maintenance software provides automatic periodic testing of
maintenance objects within the system as well as consistency tests among
the call status tables within the system. In addition, demand testing is
initiated when the system detects a condition requiring a need for testing.
Software tables are provided for storing error records. The records can be
accessed by maintenance personnel via the SAT. A Permanent System
Alarm (a serious error) causes an alarm indicator on the attendant console to
light and an error record to be stored in the error table.
Memory Allocation
The system software, like the hardware, is identified by release and version
number. Each version identifies a particular memory configuration for the
release number. Main memory is located in the Common Control circuitry.
The operating system and error log software resides on the Call Processor
circuit pack, and the remaining administration and call processing software is
on the Memory circuit pack.
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							SYSTEM SOFTWARE
Real-Time Constraints
Real-time constraints are a function of the speed of the Common Control
circuitry and the traffic load. The switch is designed so that many time-
consuming and repetitious functions are performed by processors in the port
and service circuit packs, thus relieving the common control circuits.
Traffic load, defined as the sum of static and dynamic loads, is a function of
the number of features that are executed, the frequency with which they are
executed, the system configuration, and the instantaneous (peak) call
processing load. The configuration contribution to load is known as dynamic
load. The static load consists of maintenance and audit routines.
Software Partitioning
System 25 software is comprised of various modules, each supporting a
particular process. Typical modules (referred to as tasks) include the
following:
l Administration
l Station Call Processing
l SMDR Call Record Processing
l Trunk Call Processing
l Dial Plan Manager
l Event Timer
l Save/Restore (Administration function)
l Maintenance and Audit Functions.
As shown on Figure 4-1, software tasks associated with the Memory circuit
pack are Administration and Feature Code Modules. The Feature Code
Modules includes Station Call Processing. Each task controls the storage
and movement of data and messages between associated elements within
the system.
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							SYSTEM SOFTWARE
Memory Circuit Pack
Administration: Provides for administration of station and system features.
This software also supports maintenance procedures related to checking
errors and diagnosing trouble.
Feature Code Modules: Includes the software that sends and receives data
to/from the Operating System as well as controls all voice and data features
supported by the system. Station Call Processing includes the processing of
messages and data associated with voice terminal on-hook/off-hook
indications, associated port identifications, and button and light-emitting diode
(LED) operations. The Station Message Detail Recording (SMDR) software
generates SMDR records associated with a particular call. The records are
then sent to the System RAM for storage and then to the SMDR output
channel.
Call Processor Circuit Pack
System RAM: Provides for the storage of the following:
l
l
l
l
lVariables for the various software tasks
System translations
Error Records
Feature Code Data
Stack.
Error Logger: Prioritizes and stores system errors. The errors stored in the
three error records (located in System RAM) are:
lPermanent System Alarms
lTransient System Errors
lMost Recent System Errors.
The Error Logger lights the Alarm LED (located on the Attendant Console)
when a serious error is detected.
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							SYSTEM SOFTWARE
Operating System (OS): Controls all message and data flow to/from the
Memory circuit pack and the Arch Angel Driver Interface to the
microprocessors on the port circuit packs, and to RS-232C driver interfaces.
Messages destined for a particular task are queued until the associated task
can receive them. When a task has completed a particular process, the next
message is obtained from the tasks message queue. The OS provides an
interval timer that is used to time tasks. Processes that exceed the set
interval (approximately 60 seconds) are terminated by the OS.
Arch Angel Driver Interface: Provides an interface between the OS and
Network Control (NC).
RS-232C Driver Interface: Handles the flow of information between the Call
Processor circuit pack and the systems peripheral equipment (that is,
System Administration Terminal, Digital Tape Unit, SMDR Output Device).
TDM Bus
Provides an electronic link among the system port circuits (including System
Resources) and between the Call Processor circuit pack and port circuits.
Port Circuit Packs
Each port circuit pack has on-board software that provides for the
sending/receiving of Network Control messages and data. Circuit pack
status messages are also sent to the Network Control software.
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							SYSTEM SOFTWARE
Figure 4-1. System Software Partitioning
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							SYSTEM SOFTWARE
Step-By-Step Call Description
The following is a description of a call originated between two multiline voice
terminals.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
A microprocessor on a station port circuit pack (port controller)
continually monitors associated port circuits for switchhook
status/change and button presses.
When a user goes off-hook, the port controller detects the change.
The port controller sends an off-hook up-link message along with port
identification to the Call Processor Network Controller (CPNC) via the
TDM bus.
The CPNC accepts the message and forwards it to the Operating
System (OS) via the Arch Angel Driver Interface.
The OS checks a message directory to determine which task (that is,
software module) is to receive the message. A function of the OS,
referred to as the transformer, determines it has a message for the
Station Call Processing task and queues the message in Random
Access Memory (RAM).
The Station Call Processing task retrieves its message and interprets
it as a call origination. The task determines whether there is an idle
call appearance button (System Access button) on the called voice
terminal. If so, two available time slots are reserved for the
connection.
The task sends downlink messages to the port circuit via the OS. The
messages instruct the port circuit to listen for dial tone on a specified
time slot and to light the call appearance status LED on the terminal.
When the user dials the first digit, the port circuit determines the digit
dialed. It then listens to appropriate time slots on the TDM bus for
the two tones used to generate an equivalent Dual-Tone
Multifrequency (DTMF) signal. It then removes dial tone and feeds
the DTMF signal back to the user until the user releases the button.
The port circuit sends an up-link message with each digit dialed to the
OS which routes them to the Dial Plan Manager (DPM).
The DPM collects the dialed digits and determines that the call is a
station-to-station call.
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							SYSTEM SOFTWARE
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.When the DPM collects enough digits to identify an extension
number, it stops collecting digits.
Note:If the extension number dialed is invalid, the DPM sends a
down-link message to the port circuit instructing it to listen
to time slot 07 (Reorder Tone) that is then heard by the
user. Go to Step 18.
A down-link message is sent to the originating port instructing it to
listen to time slot 06 (busy) or 08 (ringing), as appropriate. Go to Step
18 for Busy Tone or an unanswered call.
Station Call Processing sends a down-link message to the station
port circuit pack associated with the called extension to turn on the
terminals ringer and to flash the call appearance LED.
When the called party lifts the receiver, the associated port circuit
pack controller sends an off-hook message to the OS as before.
The Station Call Processing task, when it receives the message,
interprets the off-hook message as an answer.
The task sends a down-link message to the called port circuit to turn
off the ringer and to change the flashing LED to steadily lighted.
Down-link messages are sent to the port circuits assigning talk and
listen time slots for the connection.
When either of the parties hangs up, the associated port circuit
controller sends an up-link message to the Station Call Processing
task.
Station Call Processing interprets the on-hook message as the end of
the call.
The task then sends a down-link message to the port circuit pack
controllers to disconnect the time slot connections and turn off the
LEDs associated with the calls.
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							MAINTENANCE STRATEGY
Fault isolation is the cornerstone of the System 25 maintenance strategy.
Maintenance activity isolates faults to one (or more) repairable or replaceable
maintenance units. Equipment should be tested in the following order:
1.Terminal equipment
2.Station wiring
3.Port circuit packs (CPs)
4.Common control circuitry
5.Power supply and cabinet
6.Backplane.
The first fault isolation step attempts to reproduce the fault, whether it is
system-detected or user-reported. If a fault can be reprodeuced, it can be
diagnosed more easily and its correction confirmed.
Figure 5-1 presents a practical approach in responding to system troubles. If
the maintenance technician is sent to a System 25 site in response to a
trouble report, the maintenance activity will probably consist of isolating and
replacing one or more faulty units of equipment. Multiple faults recorded in
the error log and user-reported troubles may require more investigation and
analysis.
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