AXE 10 - System Description

Transcription

ERICSSON
REVIEW
PRESENTATION OF AXE 10 SWITCHING SYSTEM
THE AXE 10 SYSTEM IN THE TELEPHONE NETWORK
AXE 10-SYSTEM DESCRIPTION
AXE 10-SOFTWARE STRUCTURE AND FEATURES
2
1976
NEW PACKAGING STRUCTURE FOR ELECTRONIC
SWITCHING EQUIPMENT
ERICSSON REVIEW
NUMBER
2 • 1976 • VOLUME
53
Copyright Telefonaktiebolaget LM Ericsson
Printed in Sweden, Stockholm 1976
RESPONSIBLE
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Contents
54 • Presentation of AXE 10 Switching System
60 • Introduction of the AXE 10 Switching System in the Telephone
Network
70 • AXE 10 — System Description
90 • AXE 10 — Software Structure and Features
100 • New Packaging Structure for Electronic Switching Equipment
COVER
AXE reed switch.
Part of a printed-circuil-mounled switch board
photographed on a mirror. The integrated
circuits shown along the edge of the switch
board contain control logic, thyristors and
transistors for operating and holding of the reed
crosspoints.
Presentation of AXE 10 Switching
System
John Meurling
As an introduction to the subsequent articles on AXE this paper provides a
survey in the form of an outline discussion of the main system philosophy,
the system structure and a presentation of the most important characteristics.
UDC 621.395 722.
681.3.065
LME 83022
General structure
AXE 10 is a stored program control
telephone switching system designed
for a full range of applications for local
exchanges, tandem exchanges and
small- to medium-size transit exchanges.
The switching network is composed of
reed relay switch-blocks arranged in
three-stage subgroupings. The reed
switch is a compact, two-wire, cardmounted matrix using a unique method
of electronic operation and latching of
the reed relays. Alternatively fully electronic switches are provided—of particular interest is the digital group selector which switches 8-bit PCM.
The control uses a data processing
system in a two-level processor hierarchy with one central processor and
several regional processors. The number of regional processors is proportional to the size of the exchange. The
central processor takes care of the
complex functions, while the regional
processors perform simpler, repetitive,
functions such as scanning of test
points.
Fig. 1
AXE 10 row
Fig. 2 shows the hardware structure of
the AXE system and will serve as an
illustration for a discussion of the system structure. The main subsystems of
AXE are shown; it must however be
understood that there are several additional subsystems which are designed in software only and thus are not
shown in this diagram.
Of the switching system, APT 210,
three subsystems are shown and of the
control system or, more correctly, the
data processing system, APZ 210, also
three subsystems. An important feature is that each subsystem forms an
autonomous unit (hardware and software) of which the interfaces towards
other subsystems are standardized.
This means that subsystems may be
combined in a number of different ways
to match different applications, different functional mixes and to meet different traffic requirements. This concept of modularity is one of the most
important characteristics of the AXE
system and is found also at the lower
levels of the system hierarchy.
The subscriber subsystem, SSS, is arranged in modules for 2000 subscribers
per group. Such a group (for 2000 subscribers or, by partial equipping, 250,
500 or 1000) may be located outside
the main exchange and serve as a subscriber concentrator. The concentrator
is connected to the parent exchange
55
over two or more 30-channel PCM systems w h i c h also provide the signalling
facilities for the prolongation of the
regional processor bus, RPB.
The group switching subsystem, GSS,
is designed with reed switches. The
module in this case is one pair of RP's
to control a group of 512 inlets and 512
outlets. While retaining the GSS subsystem interfaces the reed switchblocks may be replaced by a digital
switch including in this case PCM terminals. For connection of digital lines
digital interfaces are introduced.
The trunk and signalling subsystem,
TSS, can handle a very large variety of
line- and register signalling schemes.
First choice signalling systems in AXE
are MFC (CCITT R2) and c o m m o n
channel (of the CCITT No. 7 type), but
virtually all other systems are handled,
including SxS and different revertive
pulsing schemes, so as to allow introduction of AXE with a minimum of
adaptation in existing exchanges.
Fig. 3
A X E 10 traffic characteristics
Black curves show the traffic capacity for different
SSN and GSN switch-block alternatives.
Red curves show the call-handling capacity of
the control system at 100 sees and 180 sees
mean holding time respectively
Fig. 2
A X E h a r d w a r e structure. 20,000-line exchange
SSS
LIC
SSN
AJC
BJC
RP
RPB
GSS
GSN
TSS
ITC
OTC
ASD
CRD
CSD
CPS
CPU
PS
DS
RS
PT
MAS
MAU
IOS
TW
CT
Subscriber Switching Stage
Subscriber Line Circuit
Subscriber Switching Network
A Junctor Circuit
B Junctor Circuit
Regional Processor
Regional Processor Bus
Group Switching Subsystem
Group Switching Network
Trunk and Signalling Subsystem
Incoming Trunk Circuit
Outgoing Trunk Circuit
Auxiliary Services Device
Code Receiver
Code Sender
Central Processing Subsystem
Central Processor Unit
Program Store
Data Store
Reference Store
Processor Test
Maintenance Subsystem
Maintenance Unit
Input Output Subsystem
Typewriter
Cartridge Tape Deck
Traffic properties of
the AXE system
The traffic-carrying (erlang) capacity of
the AXE system is demonstrated in fig.
3. The four horizontal lines of the diagram denote the four available SSS
alternatives, for 0.09, 0.14, 0.20 and 0.30
erlang/subscriber respectively. The
two black curves correspond to the
traffic-carrying capacities of the two
versions of the reed switch group selector; these two versions differ in
maximum size only. For example, at a
traffic of 0.12 erlang/subscriber the
exchange is equipped with 0.14 erlang
SSS groups and, with the larger GSS,
may be extended to a maximum capacity of 50,000 subscribers.
The second traffic parameter is the call
handling capacity of the control system. This depends on a number of factors, in particular the functional mix
and traffic distribution. For an exchange application with 100% key-set
telephones, 5% intra-office traffic, in-
56
ter-office traffic using MFC signalling,
certain volumes of abbreviated dialling,
toll dialling, etc, the call handling capacity is 144,000 busy hour call attempts (BHCA). For an application
with 0.10 eriang per subscriber and a
mean holding time of 100 seconds per
call this corresponds to a maximum exchange size of 40,000 subscribers. Fig.
3 includes two red curves to show
the call handling capacity in relation
to eriang capacity with functional mix
as above and 100 and 180 seconds
mean holding time respectively. For
the very large applications a separate
central processor is used for the outgoing group selector and associated
trunk and signalling functions. With
functional mix as above and a mean
holding time of 100 seconds the maximum exchange size in this case is
about 65,000 subscribers.
Fig. 4
Magazine fully equipped with printed circuit
boards for trunk circuits, control circuits and
DC/DC converter
is to say by commands from a teletype,
or, for bulk-handling, from paper tape
or magnetic tape. This capability provides the means for introducing remote control of the exchange or a number of exchanges from an administrative centre, Operation and Maintenance
Centre, OMS. In such conditions SPC
exchanges in a local network are not
staffed. Changes in data by command,
especially subscriber service categories and exchange data, replace the
traditional strapping in conventional
exchanges.
Some further factors of interest when
defining traffic and call handling capabilities of a given system are discussed in the "yellow box" on page 57.
Other facilities, notably subscriber
services, are available to cover a very
large spectrum of requirements and
may be introduced with the original installation or added at a later date. This
is often done in the form of a program
addition. In the "red box" on page 59.
are listed examples of typical subscriber facilities. The "blue box" on page 59
lists as an example the available possibilities for adopting different types of
charging schemes.
Services
AXE software system
The characteristic property of stored
program control is the relative ease in
providing a very large range of subscriber services and administrative
services. It is generally considered that
the most important feature of an SPC
system is the capability of introducing
and changing different types of exchange data via electrical signals, that
The important philosophy of the software of the AXE new generation SPC
system is discussed in a separate article. The modular structure of the software provides ease of handling and
software security. Basically the concept means that, with block modularity,
there are no globally accessible data
in the system through which software
57
Some factors affecting the traffic capacity of SPC
switching systems
The traffic capacity of the switchblocks and of the central processor
naturally depends on the desired
grade of service under normal load
and under specified overload conditions.
The maximum capacity of the system as given in this article is calculated with the following service
quality:
Fig. 6
Call-handling capacity, dependance on
complexity and idle load
tions with idle load above 20% are
unlikely.
The processing time per call depends on the functional mix of for
instance, decadic and MFC signalling, the mix of dial and key-set telephones, the proportion of internal
traffic, abbreviated dialling etc.
The call-handling capacity quoted
is valid for an environment of 100%
key-set telephones, MFC signalling
and 5% internal traffic. Higher capacities than 144,000 BHCA are obtained for cases requiring less processing power.
The call-handling capacity of a medium complexity exchange is illustrated in fig. 6, showing a certain dependence on the volume of idle load.
* Read: "Probability of delay exceeding
1 second".
' * Read: "Probability of loss".
These service quality figures will
comply with the majority of requirements. However, other requirements
may be encountered, so the traffic
capacity figures quoted should be
looked upon as examples—more
stringent service quality parameters
will result in correspondingly reduced traffic-carrying capacity and
vice versa.
The call-handling capacity of the
central processor depends on the
idle load, the required processing
time per call and on the grade of
service (under normal load and specified overload conditions).
The idle load which is a measure of
the processor time not available for
call handling, is effected by, for instance, various traffic recording and
charging facilities. A normal value
of the idle load is 10% and situa-
The service criteria and overload
definitions used in the calculations
are as shown in the following table.
Indicated in
diagram by
Solid lines
Broken lines
Probability of delay
exceeding 1 second
Normal Overload
load
1.0%
0.1%
10%
1%
The a and b lines in fig. 6 show the
dependence on the definition of the
overload:
a) 20% increase of call intensity
above normal value
b) 40% ditto
Normally the overload criteria determine the capacity. As a result the
service quality under normal load is
far better than required. As is evident from the diagram, the callhandling capacity for lower complexity
requirements
exceeds
200,000 BHCA.
58
faults may be dispersed via faulty data.
Instead, the program of a given block
can access data of the same block only. A possible software fault is immediately detected as an attempt to interwork by means of a faulty signal and
so contained within the block.
The block modularity has also been
so arranged that the function block is
the design and testing object of the
system, thus increasing the handling
capability—the programmer works only within one block at a time. Block
interwork is microprogrammed, which
eliminates the laborious address calculations and this inherent source of
software faults found in earlier systems.
AXE hardware reliability
Fig. 5
Different kinds of printed circuit boards used in
the switching system APT 210
The software security is matched by
hardware reliability provided by a redundancy strategy of duplication and
sectioning. Fig. 2 gives some indication of this scheme—the central processor is duplicated, with the two processors working in synchronous mode.
The regional processors are duplicated; their mode of operation may be
described as load-pairing, i.e. in case
of failure in one RP the other one takes
over the full load. In the switching system a sectioning scheme is used—this
is designed so that the influence of a
possible hardware fault will affect a
maximum-size group of circuits only—
such as maximum 16 trunks or 64 subscribers.
Power is supplied through DC/DC converters; the provision of these follows
the same hardware reliability structure
—each CPU, each RP, each switching
section has its own power source.
Software support
commands and printouts obeys the
same syntax as the APS languages.
This language is the Nordic MML, at
present handled in CCITT as a joint
contribution from the Scandinavian
administrations.
Naturally there are a great number of
other aids for use in all phases of design, engineering, production, testing,
installation and operation.
Mechanical design
The packaging structure, described in
a separate article, mirrors the modular
concept of the AXE system. This means
that the functional module of the system—in this case the function block
hardware—corresponds to the mechanical module, the magazine. In order to allow for the varying hardware
content there are different sizes of
magazines.
This packaging system structure provides the important feature that the
equipped magazine—as it constitutes
a well defined functional entity, the
function block—is functionally tested
together with its proper software before leaving the production phase. As
each magazine is shipped fully equipped, it will arrive on the installation
site as a fully tested unit; installation
time has been greatly reduced.
Cost effectiveness
Cost effectiveness in telecommunications equipment means minimization of
total cost. In general terms this is to
say that the sum of the yearly costs for
equipment, installation and operation
shall be as low as possible.
The software support is made up of a
number of aid systems which form part
of AXE. The most important is the AXE
language family including the highlevel programming language, PLEX.
PLEX is defined within the programming system, APS, which is the main
software support for AXE software processing.
This has been the leading philosophy
for the development of the AXE system and one consequence has been a
very determined focusing on handling.
Efficient handling is ensured in different ways, chiefly by creating a modular
system structure and by developing
powerful aids. This system philosophy
is important in all parts of the system
and many references will be found in
The man-machine language of AXE for
the fnllnwinn arHr-lpc
59
Subscriber facilities in AXE
The following list of available subscriber services in AXE is not complete—it is included to exemplify
the very wide range of functions in
the system.
—• Call barring (restricted service),
outgoing traffic.
Subscriber- or operator-controlled.
— Call barring, incoming traffic.
— Absent subscriber service. Rerouting to announcing machines
or operator. Subscriber- or operator-controlled.
— Interception service. Rerouting
to announcing machines.
— Pushbutton dialling. Dial and
pushbutton sets in parallel on
same line if desired.
— Malicious call tracing. Automatic
recording or controlled by last
party release with manual tracing. Solution depends on network
capabilities.
— Abbreviated dialling. Operatoror subscriber-controlled.
— Hot line service
— Subscriber's private meter
— Priority
— Hold for enquiry and call transfer
— Add- on conference
— Call waiting
— Automatic alarm call service.
Alarm clock.
— Information services. Recorded
announcements.
— Direct in-dialling to PABX's
—• Coin boxes
— Centralized PABX (Centrex)
Call charging functions in AXE
The AXE system will accommodate
any desired charging scheme: flat
rate, one metering pulse per call,
multimetering, toll ticketing or a
combination of two or more. Charging may be performed on local calls
only (in which case toll calls are
charged higher up in the network
hierarchy) or on local calls plus all
or parts of the national traffic.
Charging methods
— Pulse metering; different schemes, for instance according to the
Karlsson principle.
— For pulse metering the output is
produced, on command, on magnetic tape or data link to central
processing. Any individual meter, or a group, may be read out
by using special commands.
- Toll ticketing — LAMA (Local
Automatic Message Accounting).
— Continuous output per call on
magnetic tape or data link to
central processing.
Charging facilities
— Call specification on request
from subscriber (immediate service), also for pulse metering.
— Recording of outgoing calls for
charging control.
— Charging to B-party (collect).
Obtainable with toll ticketing.
— Subscribers' private meters.
Introduction of the AXE 10
Switching System in the
Telephone Network
Staffan Braugenhardt, Inge Jonsson and Bo Nilsson
In the majority of applications a new exchange system is introduced into the
environment of an existing network of exchanges and an existing administrative
system. But it must also be designed with a view to the new concepts of tomorrow.
How the AXE 10 switching system fulfils these objectives is discussed below.
The main part of the telephone network
of today is analogue and will remain so
for many years. For networks based on
two-wire transmission, the AXE system
offers analogue two-wire switching
with high quality transmission performance.
UDC 621.395.722:
681.3.065
621.395.7'!
LME 83022
8305
Survey
When introducing a new telephone exchange system into the telephone network, it is necessary to make sure that
the system will meet the demands of today and also of tomorrow. The system
must be designed for a long and useful
life, fig. 1.
Fig. 1
AXE 10 is well adapted for operation in an
environment with increasing facility level
Fig. 2
AXE 10 is an efficient and versatile component
both in the analogue network of today
and in the digital network of tomorrow
used in an economic way both for exchanges with normal subscribers and
for exchanges with advanced business
subscribers.
The AXE system can be introduced
into an existing telephone network as a
self-contained switching point without
affecting the surrounding exchanges
or equipment. But the AXE system also
meets far-ranging requirements for future networks. It is well adapted for
convenient transition of the networks
of today into the future digital networks
with advanced subscriber services and
centralized, computer-aided operation.
Today most administrations primarily
supply the ordinary telephone services.
But facilities such as push-button dialling, abbreviated dialling, in-dialling to
PABXs and extended interception are
becoming increasingly attractive and
are likely to be standard in the future.
In addition there is a whole range of
services of less obvious general importance but of great interest for selected subscribers. One such group of
facilities, intended primarily for public
administrations and the business community, includes for example centrex,
call transfer, automatic call back and
follow me.
The philosophy for the provision of
subscriber services in AXE exchanges
is a basic system with normal facilities
and optional add-on facilities which do
not affect the cost of the basic system.
This means that the AXE system can be
In the long term, however, digitalization of the network will take place,
with PCM transmission and digital
switching. The digitalization will result
in a new network structure. This structure can be described as a hierarchy
of digital group selectors at a small
number of levels to which subscriber
stages—concentrators—are connected. The concentrators are decentralized and placed near the subscribers.
Since the AXE system includes both
analogue and digital group selectors,
and has subscriber stages which can
be placed either close to or away from
the group selectors, the AXE system
is designed to assist in the transformation of the analogue networks of today
into the future digital networks, fig. 2.
Telephone companies are becoming
increasingly computerized in their administration. New exchanges must fit
into this new automated environment.
They must be able to communicatewith
the administrative system; that is, they
must be able to supply data to and
receive and execute orders in cooperation with the various parts of the administrative system, such as computers,
terminals and staff. The administrative
systems now beginning to take shape
envisage not only functions for sophisticated maintenance but also considerably increased facilities for fully automated charging and advanced traffic
recording. In this respect, too, the AXE
system is well adapted for integration
in a total administrative system. The
software structure and the input/output
organization of the AXE system are designed for the future possibility of
communication with network operation
centres and subscriber service centres
via data links.
STAFFAN BRAUGENHARDT
INGE JONSSON
BO NILSSON
Telephone Exchange Division
Telefonaktiebolaget LM Ericsson
The role of AXE in the
continuous modernization
of city telephone networks
The AXE system can be introduced into
an existing metropolitan network as a
self-contained switching point without
affecting the surrounding exchanges
and equipments or requiring changes
oradditions(except normal extensions)
in other parts of the network. However,
the AXE system also offers a number
of facilities which make it possible to
simplify and improve the network as a
whole. Some of these improvements
concern more efficient traffic handling
functions (signalling, routing etc.),
others are related to charging, operation and maintenance features. Fig. 3
shows the introduction of AXE 10 in an
existing multiexchange area.
A number of typical AXE local exchange characteristics of importance
when introducing the system in existing
telephone networks maybe mentioned:
Fig. 3
Simplified illustration of the introduction of
an AXE 10 exchange in an existing
multiexchange area, applying prevailing
signalling principles for interwork with
existing exchanges
XB
SXS
MFC
Crossbar exchange
Step-by-step exchange and signalling
MFC signalling
Naturally two-wire switching is provided, with high quality analogue transmission performance between inputs
and outputs of the exchange. This feature guarantees that traditional transmission planning rules and objectives
used for the unamplified part of the
national network today can be maintained. As mentioned earlier, AXE also
comprises digital switching facilites
for proper use in the increasing digital
environment of tomorrow.
Subscriber-loop interfacing facilities
are included, with wide range for signalling and power feeding, making it
possible to cooperate with the large
variety of existing analogue telephone
instruments. Special attention has been
paid in the AXE system design to the
use of push-button dialling in the subscriber network and also to the expected situations where a mixture of pushbutton and rotary dial instruments are
connected to the same exchange.
AXE permits the inclusion of a large
number of subscriber facilities by the
addition of functional blocks to the
basic system. This has proven to be an
economical way of solving the great
variety of different needs in different
national networks. Examples of modern
facilities obtainable as optional add-on
functions in AXE are automatic alarmcall service, abbreviated dialling and
centrex.
AXE is equally suitable for operation
in Multi-Frequency Code (MFC) networks and in the coming Common
Channel Signalling (CCS) networks.
The modular build-up of the system
facilitates its adaptation to any existing
or planned signalling method, e.g.
older type AGF network revertive pulsing or special national systems such
as the Socotel multi-frequency signalling.
Furthermore the AXE system is easily
adapted to any existing type of trunk
and junction interface for speech and
line signalling.
An increased number of routing possibilities become available when AXE
is introduced. Conventional exchanges
are limited in this respect due to a
number of factors, such as B-number
analysis depth, number of routes, number of circuits per route, number of rerouting possibilities, etc. A modern
SPC exchange, such as AXE, has practically no limitations of these kinds.
Other new possibilities available in
AXE are the flexible traffic control
features. These make it possible to
change the routing of the exchange by
command, either locally or from a central point in the network, so as to adapt
to traffic load changes and possible
disturbances.
The charging facilities are easily
adapted to the procedures already
used in the network, e. g, with a charging point for multimetering or toll
ticketing situated in a superior centre.
All facilities required for charging of
calls and subscriberservices may, however, be included in the AXE local exchange itself. This means that charging analysis, determination of tariff,
periodic pulse metering, call specification and toll ticketing can be performed
by AXE.
AXE is easily adapted to the existing
operation and maintenance organization of an administration. A single AXE
installation in an existing network may
62
be regarded as a self-contained item
with respect to operation and maintenance, i.e. all required features of this
type have been included in the basic
system. It is however foreseen that the
system will be serving to a great extent
in networks with centralized operation
and maintenance.
It is, of course, not possible to utilise
all the new facilities at the introduction of the first single AXE installation
in an existing network unless the cooperating exchanges have similar
capabilities. The concept of updating
existing crossbar installations to SPC
standards has been discussed in Ericsson Review No. 4 1973' and 3/4 19752.
AXE is well adapted to such a modernized environment, at the same time
forming an attractive link to future network concepts.
AXE as base for future
digital networks
The digital trend
Digital transmission in the telephone
network is by now well established.
Partly as a consequence of digital
transmission and partly as a competitive technology in itself, digital switching will find an increasing number of
applications. The combination of the
two will result in integrated digital networks.
Fig. 4
Comparison of typical total cost curves for
transmission and switching techniques
^ ^ B B ^
Economical range for PCM
with analogue switching
4^^^m^
Economical range for PCM
with digital switching
The effect of this integration is schematically demonstrated in fig. 4. The
figure shows the cost per circuit for different transmission media combined
with analogue and digital switching.
Assuming for the sake of discussion
that a digital group selector (including
A/D conversion) and an analogue
group selector have the same cost in
an analogue environment, the curves
for voice frequency (VF) and frequency
division multiplex (FDM) will be independent of the switching technology.
For the case with analogue switching
the interceptions of the two lines representing VF and FDM with the blue PCM
line will mark the economical range of
PCM (blue arrow). This will normally
affect only small portions of the junction network.
The combination of digital switching
and PCM transmission gives the area
represented by the red arrow. Obviously the economical range for PCM is increased. We see that PCM becomes
competitive compared to VF over all
distances and compared to FDM over
a much wider area than in the case of
analogue switching. Clearly the introduction of digital switching supports
the use of digital transmission. The use
of digital transmission is, however, one
cf the major reasons for the introduction of digital switching. It is this interactive effect which will lead to the
growth of integrated digital networks.
63
Development towards a digital
network
Digital switching and transmission
equipment can be introduced into the
telephone network in three main ways.
It can be overlaid over existing equipment, it can replace existing equipment, and it can be used to extend the
network into new areas. In principle
the overlay method means that the analogue network is extended with digital
equipment in such a way that an integrated digital overlay network is formed.
For practical applications it seems
probable that none of the methods will
be used exclusively; rather it is expected that combinations of the methods will be used in different parts and
development stages.
An example of development towards
a digital network is shown in fig. 5,
where
a) The starting point is an analogue
network with two local and one tandem exchange.
Analogue local exchange
Analogue tandem exchange
AXE 10 local exchange with digital group
selector
AXE 10 digital tandem exchange
PCM terminal
VF transmission
PCM transmission
Subscribers' stage or concentrator
Fig. 5
D e v e l o p m e n t t o w a r d s a digital network
( T h e c o n c e n t r a t o r s are assumed to be of
a n a l o g u e type)
Fig. 6
A X E 10 w i t h digital g r o u p s e l e c t o r and
r e m o t e s u b s c r i b e r stage
SSS-C
CLI
LIC
SSN
GSS-D
GSN-D
PCD
CPS
BP
ST
SSS
TSS
ETC
|TC
OTC
CSD
CRD
Subscriber Switching System-Concentrator
Concentrator Line Interface
Subscriber Line Circuit
Group Switching Subsystem, Digital
Group Switching Network, Digital
PCM Terminal
Central Processing System
Regional Processor
Signalling Terminal
Subscriber Switching Subsystem
Exchange Terminal Circuit
Code Sender
Code Receiver
b) Extension of the transmission circuits is done with PCM. The digital
signals are converted to analogue
before they are switched.
c) Further extensions of the transmission circuits are made with PCM
links. The increased digital environment makes it feasible to introduce
two digital switching centres, one
local exchange in a new area and
one tandem exchange as an extension of the existing one. We here get
the first complete digital link, without A/D conversion between two exchanges.
d) One of the analogue exchanges is
replaced by a digital exchange. A
remote subscriber stage, a concentrator, is introduced.
For stage c and onwards the network
synchronization problems must be
solved. This can be done by plesiochronous working, i.e. with autonomous
clocks in the exchanges, by appointing
one of the exchanges a master or by
using mutual synchronization.
System AXE has been designed to
serve as a basis for digitalization of
networks. As an alternative to the reed
switch the system may be equipped
with a digital group selector, thus
giving the administration the choice of
the most economic network solution,
based on actual and planned proportion of digital versus analogue equipment in the network.
A block diagram showing AXE with
digital group selector and remote subscriber stage is shown in fig. 6.
A fully digital network
In the long term it is expected that the
digitalization will penetrate down to
the subscriber network including the
subscriber set. This has potential merits both in the economic and technical
spheres. Economic gains are obtained,
as expensive technology interfaces in
the subscriber stage can be eliminated.
Technical gains will be noise and
crosstalk elimination, four-wire working on the single pair, transmission
level consistency and data capability.
64
Signalling in AXE networks
General remarks on signalling in AXE
Signal interchange with the environment is performed by two subsystems
of AXE. The trunk and signalling subsystem (TSS) is responsible for signalling on trunks and junctions. The subscriber switching subsystem (SSS)
performs the signalling funtions required to and from subscriber equipment, fig. 7.
Adaptations can be made to any signalling method by the design of proper
hardware and regional and central soft-
Fig. 7
S i g n a l l i n g f u n c t i o n s in an AXE e x c h a n g e
a d a p t e d to a m i x e d MFC a n d step-by-step
network
a
b
Receipt of digits from A-subscriber, setting
up to wanted route and signalling over
j u n c t i o n line
Exchange of signals over i n c o m i n g
j u n c t i o n line and setting up of SSN to the
B-subscriber
In neither case is the establishment of the
c o n n e c t i o n s through GSS shown.
SSS GSS
TSS
LIC
AJC
KRD
CSD
OTCi
OTC2
BJC
CRD
ITCi
ITC2
Trunk and S i g n a l l i n g Subsystem
Off-hook detection
Detection of decadic pulses etc.
Detection of tones from push-button
instruments
Code Sender for MFC s i g n a l l i n g on
o u t g o i n g trunks
Line s i g n a l l i n g on outgoing trunks
w i t h register s i g n a l l i n g of MFC type
Step-by-step s i g n a l l i n g on outgoing
trunks
Injection of ringing signal and tone,
off-hook detection etc.
Code Receiver for MFC s i g n a l l i n g on
i n c o m i n g trunks
Line s i g n a l l i n g on i n c o m i n g trunks
w i t h register s i g n a l l i n g of MFC type
Step-by-step s i g n a l l i n g on incoming
trunks
ware within these subsystems without
affecting other parts of the total system. Most variations will, of course,
apply to the signalling requirements
to and from other exchanges in existing networks. A number of different
function blocks (MFC signalling with
the associated line signalling method,
AGF revertive pulsing, decadic pulsing
for step-by-step interwork, etc.) are
therefore available within TSS in
various combinations.
The functional subdivision of the AXE
system is extremely practical for engineering and design work, e.g. for
Fig. 8
C o m m o n c h a n n e l s i g n a l l i n g C C S i n AXE 10
tandem exchange
GSN-D
ETC
PCD
ST
RP
G r o u p S w i t c h i n g Network, Digital
Exchange Terminal Circuit
PCM Terminal
S i g n a l l i n g Terminal
Regional Processor
1. 2.4 or 4.8 kbit/s
2. 64 kbit/s
3. T h r o u g h - c o n n e c t e d s i g n a l l i n g time-slot
Speech path
2.4 or 4.8 kbit/s s i g n a l l i n g path
64 kbit/s s i g n a l l i n g path
projects with new signalling requirements.
Some aspects on the introduction
of AXE in an existing MFC-network
The MFC network is a concept comprising not only the MFC signalling
system itself but also the wide range
of functions and facilities obtainable in
a network with MFC signalling.
The features of the MFC technique,
such as flexible call set-up procedure
in networks with unknown number
length, transfer of information on Asubscriber category and B-subscriber
line condition, etc. are well known.
In many national networks all possibilities inherent in the MFC system are
not utilized, partly because they are
not needed and partly because existing installations are not capable of
treating all signals that could be transmitted by MFC. When SPC technique
in the form of AXE is introduced in an
existing MFC network, a number of
new possibilities, obtainable with MFC
but not utilized in existing plant can be
considered.
Among the facilities made available by
the combination of SPC and MFC are:
— extended use of A-categories
— extended use of B-conditions
— use of signals specifying the cause
of congestion etc.
Some fundamental MFC signalling procedures in existing national networks
can be simplified or eliminated when
AXE is fully utilized. There are, for
example, extra MFC sequences required for charging purposes because the
charging point is located higher up in
the network. Backward MFC signals
(e.g. B-subscriber free, no charge) as
well as forward MFC signals informing
about the A-subscriber identity (for toll
ticketing) must be monitored or received in the charging point. These additional functions during call set-up are
today normally solved by having a regenerating and controlling MFC register in the charging point remaining connected during the whole setting-up
process. AXE may gradually eliminate
complications of the above type, as it is
capable of performing all required
charging functions itself and allows the
charging point to be located in the local
exchange.
The total call set-up time and the postdialling delay in an MFC network are
directly dependent on the time requiered for the connection of MFC
equipment and the through-connection
time of the switching stages. This is a
consequence of the end-to-end principle and of the compelled procedure
in MFC signalling. AXE here offers
further improvements in existing MFC
networks as the above mentioned
switching delays are very short compared to those in conventional exchanges.
Common channel signalling
(CCS) in AXE
When exchanges with stored program
control are introduced on a large scale,
the most attractive signalling system
between them is common channel
signalling (CCS). A new CCS system
primarily intended for use in digital
networks is presently being developed
(CCITT No. 7). Although the system will
be specified for international circuits,
it is foreseen that the main applications
will be in national networks. An international specification is expected to be
completed in 1979—80. A national application of this CCS system will be
used as standard in many future AXE
networks. The principles developed for
the new CCS system are also applied
in the signalling between the AXE
parent exchange and subscriber concentrators.
The No. 7 CCS system will be optimized
for use with the signalling rate of
64 kbit/s employed on PCM links. The
high bit rate permits simple procedures
for error control. Although the signalling system is optimized for 64 kbit/s, it
is also suitable for much lower rates
(e.g. 4.8, 2.4 kbit/s) derived from analogue circuits equipped with modems,
fig. 8. When these lower rates are used,
the maximum number of circuits served
by the CCS link will be limited, but still
sufficient to handle large routes. The
new CCS system will thus be generally
applicable between AXE exchanges
irrespective of the type of transmission
medium (digital or analogue) used in
the network.
66
channel signalling network is built
up, interconnecting the new exchanges. In this CCS network each
route may have a regular and a
stand-by link of its own (associated
signalling) or some routes can be
served by signalling links connected via another exchange (non-associated signalling).
Advantages of Common Channel
Signalling
There are a number of reasons why
CCS is expected to become a standard
signalling method in future AXE networks.
As mentioned earlier, the SPC nature
of AXE makes it possible fully to utilize
the information capability of the MFC
signalling system. However, Common
Channel Signalling together with SPC
is an important step towards the introduction of more advanced functions
and facilities in the network. The high
signalling capacity of CCS systems
means that a greater variety of Acategories, B-subscriber line conditions etc. can be transferred than in the
MFC case. Moreover, total call set-up
time and post-dialling delay are reduced as compared to MFC. The performance offered by MFC in this respect is, however, sufficient for telephony.
A CCS link intended for telephony signalling can also carry information for
other purposes. Additional services involving communication to specialized
centres can easily be introduced into
the network thanks to the flexible system structure of AXE and the presence
of CCS facilities.
CCS signalling between AXE exchanges is expected to be more economical than other signalling methods.
I n s t a l l a t i o n of t h r e e AXE 10 e x c h a n g e s in
an existing metropolitan network, thereby
i n t r o d u c i n g the first s t a g e of c o m m o n
c h a n n e l s i g n a l l i n g , CCS
This figure illustrates the performance of all
translation between CCS and MFC in exchange A.
For security and other reasons this may, however,
not be suitable in large metropolitan areas.
Signals between A and B are normally transmitted
over path A—B (associated signalling) while path
A—C—B may be used as stand-by
(non-associated signalling).
a
b
c
Existing crossbar exchanges
Installation of the first AXE 10 exchange
retaining the existing MFC s i g n a l l i n g
system,
Installation of another two AXE 10
exchanges and i n t r o d u c t i o n of CCS
between all AXE exchanges
CCS links
- ^ —
speech paths
Introduction of Common Channel
Signalling together with AXE
in existing networks
Although CCS is a very attractive future
signalling system for AXE, complications would be experienced if CCS
links were to be connected to conventional exchanges. SPC is more or less
a requirement for CCS signalling. It
may therefore be questionable whether
or not to use CCS at the introduction of
AXE in an existing network, e.g. an
MFC network.
Some basic rules facilitating the use
of CCS at an early stage may be outlined. See also fig, 9.
•
Signalling between all AXE exchanges introduced into the existing network is by CCS. A common
•
The number of translation points
between existing signalling and
CCS is minimized, so that a limited
number of the new exchanges need
be equipped for interwork with the
existing network. Calls between the
new and the existing parts of the
network are routed via these translation points.
The basic rules outlined above and the
illustration in fig. 9 are not intended as
the only solution of the mixed CCS and
MFC network. They indicate merely
that there are reasonable ways open
to an administration which prefers the
use of CCS at an early stage when AXE
is introduced into a network.
It should be noted that the existing
network used in the illustration could
be an MFC network, but also any other
type of network such as AGF or Stepby-step.
Subscriber services
A few special subscriber services are
included as standard in the basic version of AXE. One example is a simple
form of interception, without operator's
assistance, but with rerouting to a
recorded announcement or tone information. A large number of future
services are offered as options, which
can easily be introduced due to the
modular system structure of AXE.
Most of the subscriber services in
modern and future networks are performed by the AXE local exchange
itself, others will involve communication procedures using other parts of
the network. Services of the first type
are abbreviated dialling, automatic
alarm-call service, hold for enquiry,
etc., as well as PABX services including centrex. Absent-subscriber and interception services with operator assistance in a SDer.iali7ed centm are
67
F i g . 11
S e q u e n c e for subscriber-controlled insertion
of a new a b b r e v i a t e d number
*
Prefix for access to subscriber service
XX
2-digit service code
7
New abbreviated number to be inserted
08719 0 0 0 0
examples of the second type. In these
cases AXE will be equipped and prog r a m m e d with all functions required
for rerouting to and c o m m u n i c a t i o n
with such a centre.
The communication procedures used
between the subscriber and the AXE
local exchange for these services are
in accordance with the standard procedures proposed by CEPT. Most of
the advanced new services require
telephone instruments with a 12-button
keyset. Connection of such instruments
is a standard facility in AXE.
Corresponding new B-number
a
Suffix indicating end of message
Services such as abbreviated dialling,
automatic alarm-call and absent subscriber are becoming more and more
important for administrations and telephone users. These services and the
method of their performance in AXE
are described in greater detail below.
Abbreviated dialling
Abbreviated dialling means simplified
dialling for connections to frequently
used telephone numbers, by replacing
these numbers with one- or two-digit
abbreviated numbers.
The abbreviated numbers are translated into full local, national or international numbers in the originating exchange, fig. 10. A subscriber can have
a maximum of 100 abbreviated numbers, w h i c h may be either one-or two-
Fig. 10
A b b r e v i a t e d dialling in A X E 10
1
The abbreviated B-number is analysed and
translated into an ordinary B-number by the
central processor CP
2. The ordinary B-number is used during the
setting up in the network
digit. By use of the so-called suffix
method, mixed one-and two-digit n u m bers may be e m p l o y e d .
Alterations in the abbreviated number
list are made by the a d m i n i s t r a t i o n .
As an optional feature such alterations
can also be made by the subscriber,
who will then proceed a c c o r d i n g to
fig. 11.
Automatic alarm — call service
In this service a call is automatically
generated and a wake-up announcement issued to a subscriber having
requested this max. 24 hours in a d vance.
This facility is accessible to all subscribers and can be booked either
directly from his own telephone set or
via an operator. The subscriber can
also cancel the bookings himself for
the next 24-hour period.
The subscriber is rung either for 1
minute or until the time supervision expires. On encountering busy or no reply, three call attempts are made during three consecutive 5-minute intervals. If all attempts are unsuccessful,
a notification to that effect is automatically written on a typewriter.
Absent-subscriber service
At a subscriber's request, calls made
to his number during a specified
68
period can be intercepted and diverted
to a special equipment or to an operator. Rerouting facilities for this purpose are standard in AXE. The special
equipment (special information tone
generator or announcing machine) can
be located in the exchange, while the
absent-subscriber operator is normally
stationed in a specialized centre covering a number of exchanges.
The normal procedure for requesting
the facility is that the subscriber contacts the administration. He states his
subscriber number, the time and durtion of the desired service and the form
it is to take. The exchange is " p r o g r a m m e d " accordingly by the staff.
F i g . 12
Operation and Maintenance Centre OMC
with a s s o c i a t e d f u n c t i o n s
OMC
Operation and Maintenance Centre.
For operation and maintenance
activities of the exchanges in the
network
The functions below may either be included in
OMC or form Independent centres.
SA
SC + FD
SS
CH
TM
TA
NM
Service Assessment. For evaluation of
service quality provided to subscribers
Subscriber Complaint and Fault
Dispatch. Responsible for the subscriber network
Subscriber Service. For provision and
administration of special subscriber
services
Charging service. For c o l l e c t i o n and
processing of charging information
Transmission Maintenance
Responsible for the trunk network
Traffic Analysis. For c o l l e c t i o n of
statistical information for planning and
for analysis of the network
performance indicators
Network Management
As an optional add-on facility the
service can be made subscriber-controlled. This means that the subscriber
can connect to and disconnect from
the service by dialling special codes.
Centralized operation
and maintenance
To cope with the rapidly growing size
and complexity of telephone networks,
combined with rising costs for personnel and equipment, an expanded use of
automated equipment becomes necessary. A consequence of this development is the use of computers for the
control of switching systems and for
administrative routines, which in turn
leads to the logical step towards network operations centres (NOC).
Certain aspects of the SPC systems
make this step technically and economically feasible. Operational activities such as observation of system performance and changes of system parameters relate mainly to software and
may consequently be performed remotely. This means that staff must be
present in the exchange only when
hardware maintenance, such as printed
board replacement and work on the
MDF, is needed. All data transmission
to and from the exchange, including
internal and external alarms, is carried
over one reliable, medium-speed data
link.
The reliability and automated mainte-
nance characteristics of SPC exchanges give the personnel of a single
exchange very limited practice in troble analysis and fault localization. To
keep up the proficiency of the maintenance personnel it is advisable to centralize them in operation and maintenance centres. Job satisfaction is gained by the removal of routine and paper
work. Tricky and boring analysis of
paper outputs is eliminated. Centralization also makes it possible to collect
information not only about exchange
performance but about network performance as a whole, which provides
new possibilities for supervision, planning and d i m e n s i o n i n g .
A major advantage of centralization is
that activities can be coordinated between sales, operations and planning
departments. The traditional barrier
between transmission and switching
people is lowered. They can be colocated in operation centres or they
can work with identical information
from the network or from data bases.
Through this c o o r d i n a t i o n , and making
use of computer aids in central positions, the administration will be able
to attain better service at lower cost,
with all activities based on up-to-date
network information.
Administrative networks
As described above, the AXE 10 system
can be introduced in an existing network as a self-contained switching
point. This is, of course, also true of
operation and maintenance, in which
resoects AXE 10 offers all facilities required by a modern SPC exchange.
It is also possible to integrate the system as a building block in administrative networks. How this will happen
depends on several factors such as
network hierarchy, degree of automatization of switching functions, use of
SPC exchanges and existing organization.
Fig. 12 shows the connection of AXE 10
to an operation and maintenance centre OMC. Different administrative cent r e s s u c h as Central Sales Office, Billing
Centre and Directory Enquiry Centre
69
Fig. 13
Configuration of the O M C e q u i p m e n t in
a large AXE 10 network
The alarm display (T) shows the alarm situation
in the whole area. From the operator's position ©
bothway communication Is established with the
individual exchanges and detailed information is
received about different alarms etc. Printers can
also be connected to the information processor.
The communication processor transmits the
bothway data between the telephone exchanges
and the information processor and thus relieves
the load on the latter. The information processor
handles all data. Both processors are interconnected by busses.
Operation and Maintenance Centre,
OMC
Fig. 12 also shows the functions associated with OMC and fjg. 13 the configuration of the OMC equipment in a
large AXE 10 network. The different
functions shown in fig. 12 may either
be included in OMC or form independent centres.
OMC is a control point for several exchanges and also handles the data
communication with the administrative
data system and with other specialized
network operation centres. The OMC
equipment must be able to interwork
with all exchange systems in the area
and will:
— interface and automatically switch
all messages between operators,
exchanges and data bases
— perform language conversion to
command languages appropriate
to the different categories of operators
— log all I/O activities that are important as background information for
maintenance and updating of data
bases
— adapt all outputs to formats that suit
each administration
— automatize various functions resulting from operating experience, e.g.
a fault library which is consulted
automatically in typical fault situations
— store an operator's guide that is
used to simplify the work of the
operators.
The computers used in OMC are general purpose minicomputers which can
be programmed in high-level language
for appropriate functions. In large
networks it is advisable, for capacity
resons, to divide the functions between
different computers. Routine and standard functions such as data link control can be handled by a communication processor. Data base- and manmachine-oriented functions are handled by an information processor.
The alarms are displayed on a colour
TV monitor which gives a survey of the
alarm condition in the network, with the
highest alarm state displayed in colourcoded form.
Paper work is kept to a minimum
through the use of automatic logging,
analysis and search functions in the
information processor. Paper outputs
are received automatically, or on command, only when necessary.
In an initial stage the functions shown
in fig. 12, can be performed from terminals connected to the OMC computer system. The main benefits of centralization, as presented earlier, will be
available at this stage. In an extended
stage with independent centre equipment, such as TACS (Traffic Analysis
Centre System), SCCS etc. it is possible to fulfil the special needs of all
categories of personnel even in large
networks.
AXE 10 - System Description
Mats Eklund, Carl Goran Larson and Kjell Sorme
This paper surveys the background and requirements of AXE 10 and presents
the resulting architecture. It then describes the two main systems that make up
AXE 10, the APT 210 switching system and the APZ 210 data
processing system.
UDC 621 395 722:
681.3.065
LME 83022
I. SYSTEM SURVEY
Functional requirements
Stored-program-control switching systems have existed for a number of
years and valuable experience has
been gained both by operating administrations and by manufacturers. Careful analysis of this experience has provided the basic requirements for the
AXE system.
Minimization of total system cost, i.e.
including installation and operation,
must take precedence over hardware
minimization. Cost trends today show
that hardware costs, in particular IC
components, will continue to decrease,
while all types of labour costs are expected to continue to rise. This pattern
has led to a systematic effort to improve the manageability of the system
—to the creation of a system with
favourable handling properties. Handling is a general term which includes
all phases—design, engineering, production, installation and operation.
Telecommunications today are characterized by dynamic progress both in
technology and in the exchange environment—the networks. Thus the
system requires functional modularity,
so as to be introduced easily in many
different and changing environments,
and technological modularity, which
permits the use of improved techniques within the system framework.
Dependable operation is expected of
any modern switching system. It was
recognized that the reliability requirements must extend to the software as
well as the hardware—thus the reliability strategy of hardware redundance
is complemented by a corresponding
requirement for software security.
The final basic demand was for modular capacity, so that the system may be
adapted to a very wide range of sizes,
traffic conditions and functional mixes.
The maximum capacity specified for a
typical local exchange application is
40,000 subscribers at 0.10 erlang/subscriber and 100 seconds mean holding
time.
The fundamental requirements formulated above have had a decisive influence on the design of the AXE system. The following section presents
the resulting principles of the characteristic AXE system structure and its
composition and features.
Functional structure
The functional structure of the AXE 10
system forms a four-level hierarchy:
system, subsystem, function block and
function unit, fig. 1.
The characteristic feature of the functional structure is the integration of
both hardware and software in the
functional modules; these are complete as regards their functional role in
the AXE system.
Each module may be seen as a
"black box" in the system hierarchy,
having standardized interfaces with
the other modules, or boxes, on the
same hierarchy level. This means that
the module is known by its interfaces
and it is not necessary to know its division into subordinate modules. At the
function block level, for instance, system knowledge is provided by the
block interface descriptions; the function units are in this context not of interest.
At the top functional level AXE 10 is
made up of the switching system APT
210 and the data processing system
APZ 210.
AD-r 0 i n
•_
^ T 2 1 0 W l t n Subsystems
The switching system APT 210 is divided into six subsystems, fig. 2. Each
subsystem is made up of hardware and
software or of software only. The hardMvoro nm«iHog t P o o i Q ^ t r ; ^ i intorfar.ps
A
MATS EKLUND
CARL GORAN LARSON
KJELL SORME
ELLEMTEL
to subscriber and trunk lines and certain simple functions. The software is
divided into regional software for simple and high-frequent functions and
central software, which performs the
more complex functions of lower frequency. The division between regional
and central software is discussed in a
later section.
Each subsystem comprises a group
of related functions. The subsystem
grouping has also taken into account
the desire to minimize the number of
subsystems which are affected by differing environmental requirements—
for example subscriber line specifications, signalling interwork with other
exchanges, and man-machine input/
output. Adaptation to different conditions affects chiefly the subsystem SSS
and TSS in fig. 2 as well as IOS in fig. 3.
Technological developments or alternatives, such as the digital group
Fig. 2
Subsystems of switching system APT 210
Subscriber Switching System
Traffic Control Subsystem
Charging Subsystem
Operation and Maintenance Subsystem
selector may in a similar way be introduced in a subsystem without affecting
any other subsystem.
Each subsystem is made up of a number of function blocks, each of which
in turn consists of a number of function
units. At the lowest level, the function
unit, the rule is that each unit is implemented in either hardware or in software, while at the three higher levels
hardware and software are integrated.
The functional hierarchical structure
of strictly defined modules may be seen
as a "box of bricks". Engineering of the
individual exchange is greatly facilitated as everything necessary to realize a given function (or group of functions) is contained within the module
and alternative subsystems or function
blocks may be combined in a great
number of ways to meet each individual specification.
72
APZ 210 with subsystems
The data processing system APZ 210
is structured on the same principles
as APT 210 and consists of four subsystems, fig. 3. The central software
of the APT switching system is executed by the central processing subsystem, CPS. CPS is made up of a
central processor and the operative
software of, for example, the monitor,
loading and program test functions.
The regional processing subsystem,
RPS, executes the regional software of
APT and is similarly made up of the
regional processors and their operative programs. The maintenance subsystem for APZ 210 is a self-contained
subsystem, MAS, containing functions
for fault analysis, fault correction and
diagnosis.
The fourth subsystem of APZ 210 is the
input-output system, IOS, containing
functions for interworking between the
AXE 10 system and operational personnel or other data processing systems.
Input-output is performed either via
alphanumerical or file-oriented IO devices.
Controlled APT hardware
Fig. 3
Subsystems of data processing system APZ 210
RPS
CPS
IOS
MAS
Regional Processor Subsystem
Central Processor Subsystem
Input/Output Subsystem
Maintenance Subsystem
73
The diagram in fig. 4 shows the relationship in a telephone switching system between frequency of functions
and their corresponding complexity.
This analysis explains the background
to the two-level processor hierarchy.
The requirements for a favourable cost
modularity coupled with high capacity
is met by a structure with two types of
processors for different tasks. The central processor is designed for handling complex functions and the regional
processor is designed to handle simple, repetitive, high-frequent tasks. The
number of regional processors depends on the size of the exchange.
Frequency
Fig. 4
Relationship between frequency of functions
and their complexity
The function block is the most important handling module and usually
the subject for new design. The data processing system APZ 210 is structurally
and functionally designed to match the
function block concept. The software
of a function block is consequently
produced, loaded and executed on a
block basis.
The hardware structure has also been
adapted to the functional structure, and
the AXE packaging structure (BYB 101)
conforms to the modular properties of
the system.
Hardware structure
The structure of the AXE hardware is
shown in fig. 5. It is characterised by a
hierarchic division into switching hardware, regional processors and a central processor.
Extension
modules
Fig. 5
The structure of AXE 10 hardware with
duplication down to extension modules
The three types of hardware interwork
via bus systems. There is a bus system
between the central and the regional
processors, to which all regional processors are connected, and an EM bus
(Extension Module bus) between each
regional processor and the corresponding switching hardware.
Fig. 6
Software interworking between function blocks
The reliability structure of the AXE
system, see fig. 5, is based on duplication all the way down to the extension
modules. This ensures high reliability,
a single fault affecting only one extension module. The central processor
works in a synchronous parallel mode,
whereas the regional processor works
in a "pairing" mode; if a fault occurs
the other processor of the pair takes
over the full load. The bus systems are
duplicated, both between the central
processor and the regional processors
and between the regional processors
and the extension modules.
The power supply system is sectionalized, which means that DC/DC converters are included in each extension
module, and that each processor has
its own converters.
Software structure
The software structure in the AXE system follows the functional structure, in
which each module can be considered
Fig. 7
Testing of central processing units in the
development laboratory
as a "black box . The data processing
system APZ 210 has been designed on
the basis that this functional structure
is retained in the software down to the
machine code level during normal
operation.
The central software parr of a function
block consists of programs with associated data, which are stored in the
central processor stores. The programs belonging to a block have access to data in the same block only. Interwork between different blocks is
realized by transfer of messages between the programs in these blocks,
so-called signals, fig. 6.
The structure of the regional software
is based on the same principles as the
central software, but the implementation in the regional processor is simpler, as it handles simpler and smaller
programs and less data.
A new high-level language, PLEX, has
been developed for AXE in order to
simplify programming and the understanding of the programs. The processors in AXE have been adapted for
PLEX in order to achieve efficient program handling while maintaining high
system capacity. The high-level program language also contributes to high
program reliability as it makes possible
high quality software for the AXE system.
75
II. SWITCHING SYSTEM
APT 210
The switching system APT 210 performs the AXE 10 system traffic functions and associated functions for
operation and maintenance. The APT
210 structure is the same whether the
application is a local exchange, a
tandem exchange or a transit exchange. The present description is
based on the local exchange application.
Subsystem structure
As already noted and as shown in fig. 8,
APT 210 is made up of six subsystems;
these in turn are composed of function
Fig. 8
Illustration of functional structure of APT 210
SSS
GSS
TSS
TCS
CHS
OMS
AJ
AJC
AJR
AJM
Traffic Routing and Control Subsystem
Charging Subsystem
Operation and Maintenance Subsystem
A-Junctor
AJ Hardware
AJ Regional Software
AJ Central Software
blocks. Each function block is implemented in a number of function units,
hardware or software. This functional
hierarchy provides a well-arranged and
easily handled structure. The interfaces
between function blocks are strictly
defined and chosen in such a manner
that adaptation to different requirements, such as inter-exchange signalling and new facilities, affects only specific parts of the system.
The subscriber switching subsystem,
SSS, forms the interface towards the
subscriber network. Functions for receiving subscriber signalling, for power feeding and ringing are located here
together with the subscriber switch
functions.
76
The trunk and
TSS, forms the
inter-exchange
handles all the
ling functions.
signalling subsystem,
interface towards the
trunk network. TSS
inter-exchange signal-
The group switching subsystem, GSS,
contains the group selector switching
network together with functions for
path selection. GSS is normally not
affected by changes in the subscriber
or trunk environment. GSS may be
supplied in analogue or digital form.
The traffic control subsystem, TCS, is
implemented in software only. TCS
contains the central routing and analysis functions for establishing and
supervising each call and includes
such functions as, for instance, automatic call forwarding. When a function
of this type is required, the corresponding function block is included in TCS—
the interface structure is already prepared.
Fig. 9
APT 210 H a r d w a r e and software—function
blocks for traffic handling. ( O M S not included)
SSS
SS
AJ
BJ
KR
SC
Subscriber Subsystem
Subscriber Line functions
Subscriber Switching network functions
A-Junctor (unctions
B-Junctor (unctions
Key-set Code Reception
Subscriber Category analysis
GSS
GS
Group Switching network functions
TSS
IT
OT
CR
CS
AS
Incoming Trunk functions
Outgoing Trunk (unctions
Code Reception
Code Sending
Auxiliary Service (unctions
TCS
RA
RE
CL
DA
OF
Traffic Routing and Control Subsystem
Route Analysis
Register functions
Call Supervision
Digit Analysis
Optional Functions
CHS
AC
CA
MP
MR
TT
Charging Subsystem
Accounting
Charging Analysis
Metering Pulse generation
Meter Reading
Toll Ticketing
The charging subsystem, CHS, contains functions for generating and
storing appropriate metering pulses.
Function blocks for toll ticketing may
be included. Tariff determination data
are accessible via the input-output
system for resetting or additions. Subscriber meters are accessed for bulk
or individual read-out.
The operation and maintenance subsystem, OMS. The functions of this
subsystem are prepared for centralisation of operation and maintenance.
Traffic functions
General
The division of a subsystem into a number of function blocks is illustrated in
fig. 9. The function blocks may be implemented in hardware and software
or in software only. Each block is dedicated to a particular function such
Fig. 10
APT 210 H a r d w a r e — t r a f f i c routing
SSS
SSN
AJC
BJC
KRD
LIC
Subscriber Subsystem
A-Junctor Circuit
B-Junctor Circuit
Keyset Code Reception Device
Line Interlace Circuit
GSS
GSNI
GSNO
TSS
Group
Group
Group
Trunk
ITC
OTC
CRD
CSD
ASD
Code Reception Device
Code Sending Device
Auxiliary Service Device
Switching Subsystem
Switching Network Incoming
Switching Network Outgoing
and Signalling Subsystem
as incoming trunk, IT, digit analysis,
DA, etc. The hardware portions of the
function blocks of SSS, GSS and TSS
are included in the trunking diagram,
fig. 10, which illustrates the different
traffic routes through an exchange.
Function block
To further illustrate the system structure, fig. 11 shows an example of a
function block, the A-subscriber junctor, AJ. This block is made up of three
parts:
— the A-junctor hardware, AJC. This
includes circuits for reception of
dial pulses and on-hook/off-hook
signals, for current feeding towards
the calling subscriber, for sending
of dial and busy tones, etc.
— the A-junctor regional software,
AJR, which scans and controls the
AJC and performs signal recognition.
— the A-junctor central
software,
AJM, which coordinates the traffic
functions and the operation and
maintenance functions of A J .
As all block interwork is done by software signals, the hardware has obtain-
Fig. 11
F u n c t i o n b l o c k AJ
AJC
AJR
AJM
Hardware of AJ
Regional software of AJ
Central software of AJ
Fig. 12
An Extension Module, EM with 16 AJC
1 Printed circuit boards each with two AJC
2 EM control circuits
ed a clearcut structure with very few
and simple cable connections.
Extension module, EM
The APT 210 hardware is extended in
modules, EM, each containing a number of identical devices or switches,
fig. 12. The former is contained in a
magazine with up to 16 devices, c o m mon circuits for test points, operation
points and bus termination. Up to 64
EM are controlled by one d u p l i c a t e d
regional processor, RP. The extension
module, is the largest unit w h i c h can
be affected by a single fault.
Description of a traffic handling case
To illustrate traffic handling, the simple
example of an outgoing call will be described with reference to fig. 9. A call
from a subscriber is signalled on the
line circuit in LI. The subscriber c a t e gory is investigated and, if found to be
a dial telephone, connection is made
through SS to a free A J . (If the call
comes from a pushbutton telephone, a
further connection is made through GS
to a free KR.) The digits sent by the
subscriber are registered in AJ by
scanning and stored in RE.
78
After reception and analysis of a sufficient number of digits, an outgoing
trunk, OT, is selected and the path to
it from AJ is reserved in GS. If the
signalling system on the route requires
a code sender, e.g. when MFC is used,
a free CS is selected which, via GS, is
connected to the OT. Digit transmission takes place from CS via GS and
OT under the control of block RE:
switching network between the subscriber switch subsystem and the
group selector subsystem. As the current feeding and ringing functions are
placed in the subscriber switch subsystem, no DC or ringing current is
passed through the group selector,
which may thus be implemented in
analogue (reed switch) or in digital
form.
When an integrated register and line
signalling system such as decadic
pulsing is used, the signals are transmitted directly from OT under program
control.
This division has also enabled complete separation between the signalling media on the subscriber and trunk
sides. Trunk signalling variations, for
instance, will thus only affect the subsystem TSS, not GSS, SSS or TCS.
After the signalling has been completed the CS link is released and AJ
and OT are connected through the
group switch; a check is also made
that a speech path has been established through the switching network.
During the call AJ and OT are supervised by the block CL.
Simultaneously with the digit analysis,
the charging subsystem, CHS, performs
tariff analysis and metering.
Switching network
One of the characteristic features of
the AXE system is the division of the
Fig. 13
Basic analogue switchmodule in a three-stage
reed switch
number of inlets
number of outlets
size of the A-stage matrix
size of the B-stage matrix
size of the C-stage matrix
number of inlets in switch module
number of outlets or c-links
in a switch module
Switchblock groupings
The basic analogue switchblock grouping is a three-stage reed switch arrangement, A, B and C in fig. 13. In
these groupings there is always one
and only one path between a given
inlet and a given outlet—non-mesh
network. The non-mesh network simplifies path selection; the system uses
the network map principle.
The basic switch module is a PC board
with 64 crosspoint relays. This may be
arranged in different ways to form
8X8, 8X4, 1 6 x 4 or other matrices.
Fig. 14 b
R e e d switch
1
2
3
Reed relay crosspoint
Operating circuit
Latching circuit
F i g . 14 a
Function D i a g r a m of reed switch consisting
of a 2-wire r e e d relay crosspoint matrix
" ^ ~
1
2
3
Operation
Holding
Reed relay crosspoint
Horizontal control leads
Vertical control leads
Reed switch — operation and holding
The switch is a 2-wire reed relay crosspoint matrix and features a unique
method of operation and latching using
custom-designed integrated circuits.
Fig. 14 a illustrates the principle and
fig. 14 b shows a switch with 64 crosspoint relays with control logic.
Table 1
Traffic capacity of SSN for different groupings
To operate a crosspoint the control
logic indicates the Y and X coordinates
by opening the transistor Tr and the
thyristor Th,. The crosspoint relay is
operated in series with Th, from + 5 to
—8 volts. The relay is held operated by
a holding current from 0 volt in series
with Th„ and Th,. To release the crosspoint relay the thyristor Th„ is shunted
from the control logic.
The thyristors are PNPN elements and
the control logic consists of normal
TTL decoders. A component board
carries 64 crosspoint relays, one operating circuit and eight latching circuits.
The outstanding feature of this 2-wire
reed switch with electronic operation
and holding is, apart from the saving
of space, the immunity to disturbances.
This is ensured by the use of thyristors; the operation and holding functions are not affected by, for instance,
lightning-induced voltages (800 volts,
10 microseconds) or by the tripping of
a 100 volts ringing signal.
From a system point of view, for instance for test purposes, there are obvious advantages in having each crosspoint individually accessible for operation.
Subscriber switching network, SSN
Table 1 shows the matrices and corresponding traffic figures of the four
different versions of the subscriber
stage. The module is for 2048 subscribers. Transposition is obtained by
a division of the network into two parallel planes.
Analogue group selector, GSN
GSN is made up of 3-stage blocks of
512 inlets and 768 or 1152 outlets. Two
such blocks are connected together,
forming a switching module which is
controlled by a duplicated RP.
A complete group selector consists of
one or more such modules with the
links (768 or 1152 per module) evenly
distributed.
This is a full availability, high performance group selector. The permissible
traffic load per inlet has been chosen
as high as indicated in table 2 in order
to provide immunity against traffic
overload and in order to eliminate the
need for traffic equalization through
rearrangement of inlets.
Digital group selector, GSN-D
APT 210 may be equipped with a digital
version of the group selector GSN-D.
GSN-D has the same interfaces as the
analogue version; if digital lines are
connected an additional digital hardware interface is introduced.
The group selector consists of a digital
switch in a TST structure (time-spacetime) plus PCM terminals as required,
and digital line interfaces. For reliability the switch is fully duplicated so that
two planes are formed. One of the
planes can carry all the traffic; the loss
is less than 10~6. GSN-D switches 8
PCM bits in parallel.
Fig. 15 shows a diagram of an AXE 10
equipped with digital group selector.
Operation and maintenance
The major part of the operation and
maintenance subsystem, OMS, is implemented in software. OMS supervises the operation of APT and takes
appropriate action in case of disturbance. OMS includes some 30 function blocks, each of which is designed
for a specific operation or maintenance
task. The functions of OMS may be
grouped according to the following
headings.
Supervision of traffic. One important
feature of the AXE maintenance philosophy is direct supervision of live traffic. Faults or disturbances are detected and registered immediately they
occur and corrective action is taken
when necessary. An exchange thus
does not have to carry the additional
load of running routine test programs.
Certain supervision functions are integrated into the traffic-carrying hardware; an example of this is the throughconnection check of the speech path
for each connection.
The supervision of devices such as
junctors, trunks and signal devices is
based on fault counters. When the num-
Table 2
Max. number of inlets/outlets in the group
selector GSN-A at different loads per inlet and
different groupings. 2 °/oo internal loss
ber of counts per time unit exceeds a
preset quota indicating the probability
that a fault has occurred, an alarm is
given.
Transmission measurement may be
performed periodically or on command.
Testing and fault location are initiated
after receipt of alarm or subscriber
complaints. OMS includes a number of
test and fault analysis functions which
may be started automatically or on
command.
Network supervision and traffic control.
This feature is based on recording of
handled traffic and, by means of blocking and rerouting strategies, assures
that the trunk network is efficiently
utilized and that overload situations are
not allowed to spread through the network.
Statistics. Modern operational practices are based on correct and up-todate knowledge of the traffic situation
in all parts of the network. AXE 10
provides a wide range of recording
functions, including traffic measurement and traffic supervision recording
(number of lost calls). All results are
presented as read-outs periodically or
on command.
Fig. 15
AXE 10 Switching system APT with digital
group selector
PCD
GSN-D
TSM
SPM
PCM Terminal Device
Digital Group Switching Network
Time Switch Module
Space Switch Module
Analogue Speech Transmission
Digital Speech Transmission
Administration. The traditional administrative functions of an exchange performed by strapping in different parts
of the common control equipment are
in AXE 10 replaced by working with
commands via a typewriter, a display
or a magnetic tape cartridge. This
method is used for subscriber data
(number group and categories) and for
exchange data. The latter include the
engineering information on routes and
circuits, but also all the tables for analysis of route number, tariff, number
length, etc. An additional category of
special data are the individual lists for
subscribers with abbreviated dialling
facilities. These are handled by operators or, under certain conditions, by
the subscribers themselves.
Blocking of trunks or other devices is
also performed by commands to function blocks in OMS.
Centralized operation and maintenance. The structure of OMS with well
defined standard interfaces towards
the other subsystems facilitates centralization of operation and maintenance. OMS may be connected to an
operation and maintenance centre
OMC over a data channel, enabling all
commands and read-outs to be handled centrally.
82
III. DATA PROCESSING
SYSTEM APZ 210
The data processing system APZ 210
is designed with the aim of achieving
simple handling, high reliability and a
large call handling capacity. These
goals have been attained by means of
a structure that is well adapted to the
basic characteristics of AXE.
A number of small regional processors,
RP, are connected to a powerful central processor, CP, via the regional
processor bus RPB, see fig. 5. All interworking between the central processor and the regional processors is
by means of messages (signals) transferred over the bus. There is no interworking between regional processors.
F i g . 16 a
Function units of c e n t r a l processor
DS
PS
RS
CPB
RPB
MAU
CPU
TCU
RPH
ALU
BAM
MIG
PCU
TRU
DSH
LIU
PSH
UPM
RSH
SBU
Data Store
Program Store
Reference Store
Central Processor Bus
Maintenance Unit
Central Processing Unit
Table and Counter Unit
Regional Processor Handler
Arithmetic and Logic Unit
Maintenance Buffer Unit
Micro Instruction Generator
Priority Control Unit
Trace Unit
Data Store Handler
Link and Instruction Address Unit
Program Store Handler
Updating and Match Unit
Reference Store Handler
Shift and Bit Handling Unit
Fig. 16 b
Central processor C P U
RPB
The regional processors handle the
direct control of the connected equipment, such as switches, telephony
devices and 10 (input/output) devices,
whereas more complicated administrative functions are handled by the central processor.
The central processor is duplicated,
the two sides of the processor working
in a synchronous parallel mode. Hardware faults can thus easily be detected
by comparing the two sides.
The regional processors are also duplicated, every telephony device being
connected to two processors. If a fault
occurs in one processor, the twin takes
over the control of the devices.
Central processor CP
The central processor comprises the
central processor unit CPU with associated stores, and also executive programs that administer job scheduling,
program loading, storage allocation
and program testing. The executive programs work in close cooperation with
the hardware and provide the necessary service for the telephony programs.
CPU is built up of a number of selfcontained function units that are connected to a common bus, see fig. 16 a
and b.
The work of the processor is controlled
by a microprogram stored in a programmable read-only memory (PROM)
in the microinstruction generator MIG.
From MIG the other function units are
ordered to carry out the desired operations. Microprogramming has made
it possible to create powerful machine
instructions adapted to the high-level
programming language, PLEX. Auto-
83
nomous handlers in CPU interwork via
buses with the RP's connected and
with the main stores. These are of three
types, viz. program store, PS data
store, DS and reference store, RS.
They are of similar design, using dynamic MOS as storage elements.
RS constitutes a key for adaptation of
APZ 210 to the modularity of AXE 10
and to the PLEX language. Combined
with the register structure and CPU's
microprograms efficient interworking
between function blocks and high software security have thus been obtained.
The central software part of a function
block consists of programs with associated data. As mentioned before, the
data can only be accessed by the programs in its own block. Interworking
between different blocks is always
carried out between programs in the
respective blocks by utilizing special
software signals.
Only one block at a time can be active
in the central processing unit CPU, i.e.
the block having its block number temporarily stored in the block number
register, fig. 17. This number gives access to the area in the reference store,
RS, which belongs to the block. This
area contains information both about
the program start address and about
the start address of the base address
table for the block in question.
The base address of a variable contains information on location, size,
structure and other necessary characteristics. All address parameters in a
[^Relative address
parameters
© Function block currently active
© Instruction being executed
© Data elements or variables
Fig. 17
Disposition of central software stores
© Instruction for accessing
of a data element
© Data individual being accessed
84
F i g . 18
J o b s c h e d u l i n g in CP
PCU
MFL
TRL
THL
BAL
MAU
TRU
JBA
JBB
JBC
JBD
EES
Priority Control Unit
M a l f u n c t i o n Level
Trace Level
Traffic Handling Level with
sublevels 1—3
Base Level with sublevels 1 and 2
Maintenance Unit
Trace Unit
J o b Buffer A
Job Buffer B
Job Buffer C
Job Buffer D
End of Execution
program are relative to the program
start address or to the base addresses.
This means, e.g., that an absolute
address for a variable is obtained from
a base address, which is specified by
a relative address parameter in an instruction. This instruction is in turn indicated by the instruction address
register. To reach individual data in a
variable, the pointer register is used.
tained. This greatly facilitates functional changes.
A new feature is that the location of a
program with associated data may be
changed without changing its binary
code. All software is thus relocatable.
In case of a change it is thus only necessary to alter the block concerned,
while the rest of the software is main-
Job scheduling
The job scheduling in CP is carried out
mainly by microprograms and is based
on an interrupt system with four program levels and a number of job buffers for queue administration, see fig.
18.
As each block has its own base address
table with individual data, it has access
only to its own data. This simplifies the
development and handling of the AXE
10 software to a great extent and provides a powerful protection against
dispersion of faults.
85
The malfunction level MFL has the
highest priority. An interrupt signal to
MFL is generated when a fault detecting circuit has detected a hardware
fault.
Storage allocation
Program blocks are read into the central processor stores by the executive
programs, which then automatically
carry out storage allocations.
The frace level TRL is used in connection with program testing, see below.
The executive programs also contain
functions for changing the size of data
areas in the data store. This facility is
used when new subscribers or telephony devices are added to an exchange.
Such an extension is prepared by the
operator, who issues a command to
the executive programs to increase the
data store areas for the program blocks
concerned. The increase is carried out
automatically, and entirely without
operational disturbances. When necessary, the executive programs also
perform automatic storage packing to
maintain good utilization.
The normal work in CP is carried out
at the traffic handling level THL and
the base level BAL, with sublevels according to figure 18. BAL has the lowest priority. The job scheduling at THL
and BAL is based on job buffers A—D
for storing different signal messages.
A signal message contains the block
number and signal number for the receiving block and the data transferred
with the signal. When a signal message
is placed in a buffer, an interrupt signal
is automatically generated. The priority rules are that interrupt signals to
THL interrupt a job in progress at BAL
but wait until a job in progress at THL
is completed. An interrupt signal to
BAL always waits until a job in progress has been completed.
All signals from the regional processors and most signals between CP program blocks are placed in job buffers
for intermediate storage.
In addition, clock interrupt to program
level THL takes place every 10th ms
for transfer of signals to time-measuring program blocks in accordance
with information in the job table.
Program testing
For testing purposes special microprogram-controlled tracer bits are activated. With these it is possible to trace
signals between the program blocks
and also changes in the program block
data.
When an activated tracer bit is encountered, an interrupt to the trace level
takes place.
The operator can order tracing with
commands, so that interesting program sequences can be recorded and
printed out. As the tracer bits are controlled by microprograms, the processor load is increased only insignificantly.
Functional changes
The executive programs allow substitution of program blocks and changeover from the old to the new programs
without operational disturbances as
long as the signalling interfaces between the blocks and their data structures are not changed.
The duplication of the central processor may be utilized when making extensive functional changes in the software. One processor is then halted and
loaded with the new software, after
which a changeover is ordered so that
the newly loaded processor takes over
the operation. Operation is disturbed
only insofar as calls in transition states
are cut off. Connections that have already been established are not affected.
Regional processor, RP
A number of regional processors are
connected to the central processor via
the duplicated regional processor bus
RPB. The regional processors perform
simple routine tasks that require large
capacity, such as scanning of test
points and control of relays.
The processor comprises a central
processing unit, CPU, a data store, DS,
a program store, PS, and executive
programs for administering and supervising program handling. CPU consists
86
of a number of independent function
units connected to a common bus, fig.
19 a and b. The work of the processor
is controlled by a microprogram stored
in a PROM memory.
A number of extension modules, EM,
are connected to the CPU via a bus
EMB. An EM comprises a number of
Fig. 19 a
Regional processor RP
Fig. 19 b
Structure of regional processor RP
EMB
RPB
CPU
PS
DS
EMBU
ALU
PRU
IBU
MIG
PSH
DSH
OBU
RPBU
Extension Module Bus
Central Processing Unit
Program Store
Data Store
EM Bus Unit
Arithmetic and Logic Unit
Process Register Unit
Input Buffer Unit
Micro Instruction Unit
Program Store Handler
Data Store Handler
Output Buffer Unit
Regional Processor Bus Unit
telephony devices or IO devices of the
same type, or a part of the switching
network. Two RP's control the same
EM, though only one at a time.
The RP program store is divided into a
number of program pages. One program page is used for the RP executive
programs. In addition one program
87
page is normally required for each type
of device controlled by the processor.
Each EM is allotted a continuous area
in the data store. The start address of
the data store area of an EM is stored
in a base address table at the beginning of the data store.
Job scheduling
A program stored in a program page in
an RP interworks with the corresponding program block in CP with signal
messages over the bus, RPB. CP
fetches the signal messages by continuously scanning all connected RP.
All address translation in connection
with the signalling (block numbers and
device pointers in CP, EM numbers
and internal device pointers in RP) is
done automatically by the CP microprogram that administers the transfer
of signals to and from RP.
Programs are called in cyclically and
this is administered by the executive
program. The cycle period is usually 5
ms and constitutes the primary interval of the regional processor. During
the primary interval the executive program scans all EM and calls in the
corresponding programs in turn.
Maintenance system
The maintenance system in APZ 210
contributes to the high operational
reliability that is necessary for telephone exchange applications. The
maintenance programs work in close
contact with the hardware and make
use of built-in redundancy in the central and regional processors.
Each central processor contains builtin fault detecting circuits of the following types:
a) side-indicating supervisory circuits
for, for example, parity check of
stores and buses, as well as voltage and time supervision. In case
of a fault these circuits directly indicate the faulty processor side.
b) side-comparing supervisory circuits
that detect faults by comparing
data sent over the internal buses of
the two central processors.
c) program supervising circuits that
detect, by time measurement, when
the processor program handling
does not operate normally.
In addition, maintenance programs
carry out routine checks of the central
processor hardware.
When a hardware fault is detected in
CP, a fault signal is sent to the maintenance unit MAU. If a faulty processor
side is indicated, MAU automatically
halts this side and allows the other
side to continue immediately with the
traffic handling. If the fault is a comparison mismatch, MAU interrupts the
work in progress and initiates a sideindicating program in both sides. The
processor side that cannot execute this
program correctly is halted by MAU.
The interruption time necessary for
identification of a faulty side is less
than 20 ms. Thus hardware faults in
the central processor are normally
handled without traffic disturbance.
A simple and reliable method of fault
diagnosis is based on the fact that
blocking and deblocking of the CP
function units can be controlled by
programs. When a processor side has
been blocked after the detection of a
hardware fault, the function units can
be deblocked automatically, one by
one, until a new fault signal is obtained,
which directly and reliably pinpoints
the faulty unit.
A number of program operation checks
have been incorporated in the microprograms, which' has been facilitated
by the structure adopted for APZ 210.
This assures early detection of faults
and minimizes fault dispersion, thus
securing a high software quality.
The regional processors are duplicated
so that each processor in a pair normally controls half of the common
EM's. Each RP has its own supervisory
circuits for parity checks and time supervision. In addition, both central and
regional routine test programs are provided for the supervision of RP.
88
When a fault is discovered in an RP, the
work in progress is automatically interrupted and a fault signal is sent to
the maintenance programs in CP. Depending on the extent of the fault CP
then transfers the control of the EM's
concerned to the regional processor
that is not faulty.
way a simple command is written is
given below:
For certain serious faults a system restart is carried out, which means that
traffic handling is resumed from a well
defined starting point.
Print-outs can be guided to various
devices in a simple way since all printouts are classified with a number of
function codes. By means of a command the operator can guide print-outs
belonging to a certain class to one or
more given IO devices.
If a number of system restarts take
place within a short time, all software
is automatically reloaded from magnetic tape. However, a system restart
usually affects only calls that are in
process of being set up, while established calls are not affected.
10 system (IOS)
Fig. 20
4 K9 memory board
The 10 system comprises functions for
transfer of information between APZ
210 and the operator or other computer
systems. During the design work the
most important goals were to achieve
reliable man-machine communication
and good flexibility for future technical
developments.
The 10 system is divided into blocks
in accordance with the AXE 10 function block structure. The IO system
contains a number of administrative
program blocks and also a function
block for each type of IO device. The
device blocks contain central and regional software and the corresponding hardware. The regional software
carries out the direct control of the devices while the central software handles administration and processing of
information.
A special command language has been
developed for AXE. When designing
the language, regard was paid to the
standardisation work in progress within
CCITT. As a result of the logic structure of the language, the analysis of
commands is to a great extent done in
the IO programs. This prevents the
user programs being affected by any
syntactic changes. An example of the
LAPBL: BLOCK = ABC, IODEV = C T 1 ;
The command orders the read-in of
program block ABC from magnetic
tape cartridge reader no. 1,
Conclusion
The two most important features of the
AXE 10 system are the functional modularity with integrated hardware and
software and the provision of alternative analogue and digital switchblocks
in the group selector.
The functional modularity is the basis
for obtaining a system with substantially improved handling properties.
Functional modularity is also the
means for software security, the characteristic of the new generation SPC.
AXE 10 offers a very wide range of subscriber services and, equally important,
the administrative facilities that open
the way to centralization of operation
and maintenance.
AXE 10 is thus ideally suited both for
today's modern networks and for the
networks of tomorrow, the networks
with an increasing proportion of integrated digital switching and transmission and with highly sophisticated, centralized operation and maintenance.
89
Technical data for APZ 210
COMPONENTS
AXE 10-Software Structure
and Features
Goran Hemdal
This paper describes the structure of the AXE system with emphasis on the
characteristic functional modularity. This unique structure provides the basis
for the two outstanding features of the system—software security and ease
of handling.
U D C 621.395.722:
681.3.065
681.3 06
L M E 83022
Fig. 1
E x t r a c t f r o m the p r o d u c t s t r u c t u r e of
t h e AXE s y s t e m
SSS
AJ
AJC
AJR
AJM
RP
CP
Subscriber subsystem
A-junctor functions
AJ c i r c u i t
AJ regional software
AJ central software
Regional processor
Central processor
Experience gained from SPC systems
of the generation at present in service
has shown that the problems encountered in handling the software of the
systems have been greatly underestimated. When developing the AXE system software one of the basic reguirements was therefore the elimination of
the bulk of traditional software problems by creating a system in which
software handling is simple and which
at the same time provides high operational security.
One of the most important features of
the AXE software is its modularity,
which directly corresponds with the
functional modularity of the system.
This modularity allows every software
module to be independently programmed while at the same time ensuring
that the modules will work together.
As the modules are small and a high/
level language is used for the programming, a very high program quality is
obtained.
As, furthermore, the functional modularity is maintained in the implementation of the software, every software
module may be separately compiled
and loaded. Storage allocation is performed as part of the loading activity
on the target processor. This will facilitate the software handling, especially
under normal service conditions, for
instance for functional changes, when
any disturbance of the normal service
is avoided.
Software structure
Functional module and product
In order to provide ease of handling in
combination with high software security the AXE system software is integrated into the functional modules of
the system. Each such module (system,
subsystem, function block or function
unit) is defined as a product. Together
the products form the product structure of the AXE system, fig. 1.
Viewed from the aspect of the remainder of the system, each such individual
product is considered a "black box"
with unambigously defined interfaces
with interworking products.
The interface contains all the different
signals which the product may send
and receive during operation. A signal
signifies the transfer of information, at
this stage without regard to the method
of transfer.
For every product the interface of the
product is strictly defined, enabling the
product to be used as a building block
for higher-level products.
Every product of the system, subsystem and function block level is assembled from the products on the next
91
GORAN HEMDAL
ELLEMTEL
lower level. A specification of these
products therefore contains only references to the appropriate specifications of the products on the next level.
The interconnection of the interface of
every subordinate product to the interface of every other subordinate product, as well as to the interface of the
product itself, is however specified in
detail.
In order to enable automatic processing of engineering activities, such as
determination of the products involved
for a particular AXE exchange, a product specification also defines the
necessary exchange assembly parameters. For every parameter the method of passing the value of the parameter between the products on different levels is specified. By means of
these exchange assembly parameters,
Fig. 2
Example of two functional alternatives
for one product
functional alternatives may be specified. Fig. 2 shows two examples of
specification of function block X.
The total product structure for the AXE
system defined by the product specifications enables an automatic translation of the functional requirements of
any particular exchange to the appropriate product configuration satisfying
these requirements. The strictly defined interfaces and their equally strictly defined interconnections ensure
that every product configuration obtained is also a working configuration.
A product specification on the function
unit level differs from the specifications on the higher levels with respect
to the internal structure, which is specified in relevant hardware or software
terms.
92
Hardware function unit
This unit consists of a number of identical devices, fig. 3, for instance trunk
circuits, code receivers, etc. Interworking with other connected hardware
function units is performed by hardware signals, that is to say the information is transferred by, for instance, pulses or combinations of frequencies on
a physical transmission path.
Software function unit
This consists essentially of a number
of identical "devices" which may be
divided into a program part and a data
part. The program part consists of a
sequence of program instructions—
the program logic of the device, while
the data part contains information
about the state of the device, linkages
to other devices, etc. These data are
stored in data elements of lengths
suited to the information. In the AXE
system each such data element is defined as a variable.
Fig. 3
Principal structure of a hardware function
unit with n devices
Fig. 4
Principal structure of a software function unit
with records corresponding to n devices
Both the program part and the data part
of a software function unit are stored
in the memories of the processor which
executes the logical functions. As it is
unnecessary to duplicate identical information, the program parts of all de-
vices form one common program. In
the same way, sections of the data
parts are combined in common data,
while data that are individual for each
device form individual data, fig. 4.
The variables, which form the common
data of the function unit, are directly
accessible from the program. For individual data, on the other hand, the
variables are organized in a record for
each device. To reach an individual
variable the device in question must be
indicated first. In AXE the necessary
indication mechanism is defined as a
pointer.
No detail of the program and data
structure of a software function unit is
accessible from outside, all interwork
with other function units is performed
by signals. As a consequence no globally accessible data exist in the system.
Every software function unit can therefore be programmed independently,
while the product structure ensures
that the function units will interwork
correctly. Program errors are effectively prevented from mutilating data belonging to other function units. As a
consequence both programming and
debugging are simple.
93
Software signals
As the information carried by the signals between a software function unit
and interworking function units is
transferred by software means, these
signals are referred to as software
signals.
Transmission of a software signal is
specified as an instruction in the program. This instruction associates the
variables and constants of the sending
function unit with the information
Fig. 5
format of the signal. In this way the
values of the variables and constants
are transferred as signal information
although the variables and constants
themselves are accessible only within
the sending function unit.
Reception of a software signal is also
specified as an instruction. The function of this instruction is twofold. The
instruction as such indicates the location in the program where program execution is to start when the signal identified in the instruction is received.
Secondly the instruction asociates the
information format of the signal with
the variables of the receiving function
unit, thereby making the signal information accessible.
Principles of function unit interworking
Software signals are always interchanged with the help of the processor, fig. 5. This processor may transfer
the signal to another software function
unit executed by the same processor,
to another software function unit executed by another processor or to a
hardware function unit. The necessary
transformation from software signals
to hardware signals is performed by
the processor. In the same way hardware signals are transformed to software signals when transferring signals
from a hardware to a software function
unit.
Hardware signals
Software signals
94
Software implementation
Implementation principles
From the customer's point of view the
characteristics of a system during
normal service are far more important
than the characteristics during specification and design.
In order to obtain the manageability
and software security required of the
AXE system, the functional modularity
must be maintained in the implementation of the system. One possible
way of achieving this would be to provide each software function unit with
its own processor.
For technical and economical reasons
this is not feasible today. It is however
possible to design a processor so that,
although a number of function units
exist in the same processor, this processor provides exactly the same
characteristics for each function unit
as if it had its own processor.
Fig. 6
Function block structure
An analysis of the software functions
of an SPC system leads to a division
into highly frequent simple functions
and complex functions of low frequency.
For technical and economical reasons,
therefore, it was advantageous to structure the data processing system APZ
210 of the AXE system as a hierarchy
with two types of processors—central
and regional processors. The central
processor is designed to execute the
low-frequent complex functions, while
the regional processors are geared to
the performance of repetitive simple
functions.
There are thus three types of function
units in the AXE system—hardware
function units, regional software function units and central software function
units. The regional software function
units are used, for instance, for scanning test points and operating relays
in hardware function units and can only interwork with hardware function
units or central software function units
within the same function block. Interworking between different function
blocks is as a rule performed by software signalling between central software function units.
A function block can thus consist of
any combination of central software
function units, regional software function units and hardware units, fig. 6. As
it must be possible to choose the most
suitable combination of implementation techniques for any function, ii._
function blocks have been selected as
the normal handling products. Both the
central and the regional processors of
the APZ 210 system are therefore
geared to the function blocks.
Implementation of central software
Only one function block at a time may
be active in the central processor. For
this reason each function block is assigned a unique block number. The
central software of a function block is
active only when its corresponding
block number is found in the central
processor block number register, fig. 7.
With the aid of the block number a
fixed reference table in the reference
store of the central processor is accessed. The following information relating to the function block iscontained
in this table:
—• the state, e.g. normal operation
— the program start address, giving
the absolute address to the area
where the programs of the central
software unit belonging to the block
are stored
— the base start address, providing
start address of the area where the
base addresses for the variables of
the central software unit belonging
to the block are stored.
The program of the function block begins with a signal distribution table.
Each signal to a block is identified by a
signal number which is unique within
the block. The number of a received
signal is translated to the correct entry
position with the aid of the signal distribution table.
The base address contains, among
other things, the absolute address of
the variable in the data store, the length
of the variable, information as to whether the variable belongs to common or
individual data
a n r i in the- l a t t e r
racp.
95
the number of devices. When an arbitrary variable is accessed, only the
number of the variable within the function block base address table is given
in the instructions, whereafter the
microprograms of the central processor perform the necessary address
calculations.
for every function block may be compiled separately, while at the same time
the machine code obtained from the
compilation is fully relocatable. All
memory allocation is therefore performed by the central processor itself
in connection with the loading of the
central software.
At the same time the microprogram
checks that the resulting absolute
address in the data store really is situated within the area assigned to the
current variable. Each variable thus
has its individual memory protection.
As accessing of variables belonging to
other function blocks is prohibited by
the central processor hardware, and as
each variable has its own individual
memory protection, powerful protection is obtained against the dispersion
of software faults. At the same time
the probability of locating program
faults already during system testing
has been substantially increased.
By designing the machine instructions in such a way that they always
refer to quantities in relation to current
start addresses, the central software
Fig. 7
Implementation of central software
BS
PSA
BSA
Block State
Program Start Adress
Base Start Adress
96
Implementation of regional software
A regional processor stores and executes the regional software in the same
way as the central processor. In this
case the procedure is much simpler as
there is no interworking between different function blocks in the regional
processor.
The regional software of a function
block is stored with the program in a
program page in the program store of
the regional processor, and the data is
stored in a continuous area in the data
store, fig. 8. There are in this case no
base addresses as in the central processor, but as the variables within a
record form a continuous area where
each variable is defined by its position
within the record, the same advantages
are obtained as in the central processor.
Software representation
Source documents
The software of the AXE system is represented in the form of source documents. These source documents specify the different types of software information used in the AXE system and
they consist of signal documents, function unit documents, product structure
documents and project documents.
Fig. 8
Implementation of regional software
The signal documents
specify each
software signal as to its properties, the
format of the transferred signal information, etc.
The function
unit documents
specify
the internal structure of each function
unit, i.e., among other particulars its
data structure and program logic.
The product
structure
documents
specify the internal structure of products above the level of the function
unit.
The project
documents
specify the
selection of a c o m b i n a t i o n of working
products for a specific exchange taken
from the total collection of the AXE system as specified by the product structure and function unit documents.
Current source documents are handled
with the aid of the programming system APS 210. The object is of course
to obtain, in target code form, the software of a specific exchange.
Language family
APS 210 defines necessary source document languages in the form of a language family, w h i c h includes the special source languages SPLEX, PLEX,
ASA 210C, ASA 210R and CLAPS, fig. 9.
97
SPLEX includes facilities for declaration of signals and the internal structure of the products, while PLEX c o n tains facilities for specification of program logic.
PLEX is a high-level, machine-independent programming language for SPC
systems and, apart from normal highlevel language facilities, includes facilities for signal sending and reception
and pointer handling.
A S A 2 1 0 C and ASA210R are the respective assembly languages for the
central and regional processors of
APZ 210.
CLAPS includes the necessary control
and editing directives for handling
APS 210 in the design, engineering,
production, etc. of the AXE system
software.
Software production
The application programs are initially
written in the high-level language PLEX
and their formal correctness is analysed by the APS 210 programming
system. A check is then made that the
signal reception and
transmission
statements match the corresponding
signal formats specified in the signal
documents written in the SPLEX language. This is an absolute requirement
before any software function unit may
serve as a building block.
The programs are also tested on the
source code level (PLEX), thereby
eliminating almost all program errors
at an early stage. The p r o g r a m m i n g
system APS 210 provides the necessary printouts of the source code as
well as of analysis and test results, fig.
10.
When producing the object software
for APZ 210 in a specific exchange, the
exchange assembly parameter values
contained in the project document for
this exchange are used for specifying
the actual functional requirements.
With the aid of the product structure
documents these values are translated
into a list of all products to be included
in the exchange. At the same time the
block and signal numbers are assigned. APS then compiles the software for
each function block separately into
object code, which is normally stored
on cassette tape. The same cassette
tape may contain one single function
block or any number of such blocks.
A printout of the object code is also
obtained, in which every instruction is
listed both in binary machine (object)
code and in ASA210C assembly code,
fig. 10.
AXE
Fig. 9
Software languages and their usage
SPLEX
PLEX
ASA210C
ASA210R
CLAPS
Specification Language for Exchanges
Programming Language for Exchanges
Assembly language of the APZ 210
Central processor
Assembly language of the APZ 210
Regional processor
Control Language for APS
98
Exchange-dependent data are not
specified in the source code and will
consequently not be included in the
object code. Instead, the exchangedependent data are loaded separately
with normal commands.
coding in PLEX. As APZ 210 is
adapted to the functional structure
of SPC systems, efficient machine
code is generated from programs
written in PLEX. Only purely machine-dependent parts of the operative programs in APZ 210 are written in assembly code.
Software characteristics
program security. The functional
structure of APZ 210 combined with
the addressing principle provide
an efficient limitation to inadvertent
programming faults. Such faults are
consequently few and easy to find
during program testing.
The functional orientation in the structure of the AXE system software, combined with the functional structure at
target code level of the data processing
system APZ 210, provides the software
with a number of important features
such as
— structured system engineering. For
system design a functional structuring is performed, in subsystem,
function block and function unit.
Programming is done only at the
function unit level.
Fig. 10
Software production activities
high program quality. The principles of program design as listed in
the points above, plus the use of
sophisticated aids, such as the
programming system APS 210, for
design, testing and production of
software, guarantee a high quality
of the AXE system software.
99
— function blocks compiled separately. Because of the functional structureeach function block iscompiled
separately. This means that, for
example when correcting possible
program faults, a new version of
the function block is compiled and
exchanged for the faulty one. Thus
"patches" are avoided.
— functional blocks loaded separately. As all target code is relocatable
in the memories of the data processing system, all memory allocation
is done in connection with loading
the software on the target machine.
This means that, for example, most
functional changes are performed
during normal service, without traffic disturbance.
— exchange data loaded by commands. All exchange data are loaded by commands. This means that
all types of extensions are effected
directly on site without the need of
an administrative computer.
Fig. 11
Loading of a cartridge unit
— functional signal tracing. All signals
between the different function
blocks of the AXE system may be
traced. This enables the maintenance personnel to locate functional faults to the faulty unit without having to use the detailed software documentation.
Conclusion
The functional modularity of the AXE
system, which is maintained in the implementation of the system, gives the
AXE system its outstanding flexibility,
manageability and software security
for all phases of design, engineering,
production and installation, as well as
during normal service.
With the AXE 10 system it has therefore
been possible to attain all the original
objectives of the SPC technique.
New Packaging Structure tor
Electronic Switching Equipment
Rune Alexandersson and Hans 0. Rorstrom
The design of a new mechanical packaging structure for electronic switching
equipment was initiated at the same time as the AXE system project was started.
This meant that the functional concept of the AXE system influenced
the packaging structure. As a matter of fact the mechanical structure should
be seen as an integral part of the AXE system. It contributes to a
very large extent to the outstanding AXE system features which provide ease
of handling—in production, design, testing, installation and extension.
This paper gives a brief presentation of the main characteristics of the
mechanical structure.
UDC 621 395 722:
681.3.065
621.3572
LME 738
83022
The basic requirement for the design
of the new packaging structure was
to provide a suitable structure for predominantly electronic equipment with
components of the IC type, but also
with miniature electromechanical components and various special devices,
such as power packs, fig. 1.
At the same time it should be recognized that modern system design, documentation and production impose a
particular set of requirements because
of the use of computerized aids in all
the different handling processes.
These technical requirements are naturally coupled to certain economical
guidelines. In the present case the
main emphasis has been on the minimization of total cost, including installation and operation, rather than on
Fig. 1
AXE exchange. The mechanics are painted
in two shades ot grey—a basic light grey and a
darker matt shade for end covers and cable
section doors; power converters and markings
are blue
trying to develop a packaging structure
that might seem economical as a subsystem but would not permit the exploitation of the economical potential
of the total system. Total cost minimization has been reached by designing
the packaging structure in such a way
that the functional structure of the AXE
system is maintained in the mechanical design. In practice this means that
the functional module of the AXE system—which is also the module used
for design and documentation—is
identical to the mechanical module,
the magazine. This unique property of
the integrated system has meant that
the traditional rack, with its wiring,
testing and documentation, has been
eliminated—the main unit is the magazine corresponding to the hardware of
the function block.
Requirements
The mechanization and standardization of the handling activities in design
and production also mean corresponding handling improvements for the telephone administration. For instance
operation and maintenance are simplified, as also are planning and execution of all forms of extensions or functional changes. However, the extensive
use of computer-based handling aids
101
RUNE ALEXANDERSSON
HANS O. RORSTROM
Telephone Exchange Division,
Telefonaktiebolaget LM Ericsson
in large-scale production must not exclude the possibility of producing the
AXE system in local factories or running it in networks largely using conventional methods.
Examples of typical activities which to
a great extent are computerized are
printed board design and production,
production of wiring tables for magazine backplanes, production of testing
programs and cabling tables.
Table 1
UNITS OF MEASURE
Basic unit
Building module
1 M = 2.54 mm (M = Module)
1 BM = 16 M = 40.64 mm
For production tooling the mechanical
design has many advantages, as the
structure is very simple. Production
methods are thus easily adjusted both
to the almost wholly manual handling
of short series and to the fully automated production techniques for long
series. Local production of the packaging structure can therefore easily be
arranged.
As the structure is modular, so that a
large number of units are composed
of a basic assortment of a few mechanical details, the spare parts handling
as well is simplified.
Functional structure
The functional hierarchy of the AXE
system is seen in fig. 2, showing the
four levels: system, subsystem, function block and function unit.
The hardware structure is divided up
in the same way. The function block
with its documentation corresponds to
the magazine, which forms the handling module, with its documentation.
The function blocks vary in size and
therefore it is necessary to provide a
series of different magazine sizes. In
traditional rack design this would not
be feasible; instead a shelf structure
has been developed in which magazines of varying sizes are mounted—
there is obviously a very large freedom
of choice of combinations.
Fig. 2
Functional hierarchy of the AXE system
(Blue)
hardware
(Yellow) regional software
(Red)
central software
The advantages of these new concepts
in telephone exchange construction
are apparent in all phases of handling.
In production these units, magazines,
are equipped with their printed circuit
boards and tested as functional units.
They are then packed and shipped,
with the PC boards in position, and
arrive on the installation site as fully
tested functional units—one result of
this practice is considerably reduced
installation handling, especially testing, and appreciably reduced installation lead times.
The use of different combinations of
mechanical piece-partsout of the basic
assortment is governed by design rules
based on modular concepts.
The packaging structure is adapted for
both electronic and electromechanical
components. The unit of measure for
the basic module is 1 M = 2.54 millimetres. The building module 1 BM =
16 M = 40.64 mm has been introduced
to facilitate handling of the larger modular measures, table 1.
The designations for the different parts
of the structure will be found in table 2.
The designation BYB 101 is also used
collectively to denote the complete
packaging structure.
The magazine is defined as a unit
which contains a number of printed
board assemblies and also interconnects the boards electrically. The row
structure mechanics constitutes all the
mechanical piece-parts used to form
a row with its shelves, cable chutes etc,
which accommodate the magazines,
cabling and so on.
Characteristics of the
packaging structure
The features of the BYB 101 structure,
as described and used in a functionally
modular' way, may be summarized in
the following points:
•
•
•
•
•
•
•
•
•
•
common mechanical, electrical and
functional interfaces
documentation adapted to handling
racks replaced by magazines
flexible grouping of magazines
cabling separated from and independent of the row structure
standardized "connectorized"
cables
all cables connected from the front
decentralized power distribution
good heat dissipation properties
attractive and modern external design.
102
These points are explained and discussed briefly in the following paragraphs.
Common mechanical, electrical
and functional interfaces
This means that a certain electrical
function corresponds to a mechanical
unit. This correspondence has advantages in all stagesof handling of the
Fig. 3
PC Board magazines. The magazines are made
up of two main components—the board
trame(s) and the back plane (wiring unit)
Fig. 4
Printed board assemblies
product. The various handling activities
are design, documentation, production,
testing, shipping, installation, and operation and maintenance. This common
interface is obtained by the modular
flexibility of the mechanics, providing
a range of magazine sizes to suit different functions. There is a series of
magazines for from 5 up to 62 printed
boards, figs. 3 and 4.
103
I
Fig. 5
Documentation adapted to handling
Documentation adapted to handling
This is a natural consequence of the
coinciding of interfaces. There are
in principle no documents that extend
outside the handling module, the function block. A documentation structure,
defined per type of product, regulates
the types and numbers of documents
necessary for each unit. This structure
increases the possibilities of data processing of the documentation. The use
of new documentation media is foreseen, for instance, in the form of centralized data bases, fig. 5.
Racks replaced by magazines
The traditional rack in the form of a
vertical structure with its own documentation, wiring, testing, etc. has
been eliminated in the BYB 101 equipment practice. Today the board magazine is the major mechanical, wiring
and functional unit.
Fig. 6
Row structure principle
The row structure is a new concept.
The total length is decided by the exchange size and application and by the
available space. The row is subdivided
into smaller units, called sections, of
two types—shelf section and cable
section. The shelf section consists of
horizontal shelves on which the magazines are placed. The shelves also carry
the horizontal cables to the magazines.
The cable section is a vertical unit in
which the cables are run from the
cable chutes along the top of the row
to the respective shelves of the shelf
section. The row may be single- or
double-sided, fig. 6.
The different combinations of shelf and
cable sections are practically unlimited. Thus it is always easy to adapt the
mechanical structure to any desired
size or application.
104
The row mechanics is a standard product which is delivered from stock directly to the installation site, fig. 7.
Fig. 7
Row structure mechanics, main components.
The verticals form the framework of both
shelf and cable sections. The front and back
covers are used for protection and air guiding
and also form an attractive exterior
Fig. 8
Flexible arrangement of magazines—
horizontally and vertically
Fig. 9
Modular building elements of a magazine.
(From left) wiring unit width 15 BM, board frame
3 BM and board frame 9 BM
Flexible grouping of magazines
Magazines may be placed beside each
other, horizontally, or above one an-
other, vertically, like books on a shelf.
It is thus easy to find the particular
grouping which requires minimum
cable lengths and floor space. Alterations or extensions are also easy to engineer and execute—magazines can
be replaced or moved without change
of the row structure mechanics, fig. 8.
105
11
L
-i.
L
Fig. 10
Cabling separated from row structure
Cabling separated from row structure
As mentioned, the row structure includes no cabling; all connections between magazines are made with plugin cables, one of the prerequisites for
flexible magazinegrouping. Installation
is simplified as separate documentation is used for the mechanics and for
cabling. The row structure mechanics
is system-independent, fig. 10.
Standardized "connectorized" cables
The number of different cable types
has been restricted in order to simplify
cable handling. The cables are always
manufactured on the one-to-one prinprinciple, i.e. pin 01 at one end is connected to pin 01 at the other end, pin
02 to 02, etc., fig. 11.
Fig. 11
Standard plug-in cables with pin-to-pin
interconnection
Fig. 12 Below
Bus cable. For 24 and 16 pair buses
Fig. 13
Signal cables, with connectors. (From top)
32, 16, 12, 8 and 4 pair cables
The cabling principle results in a minimum of contacts in each wiring con-
nection and thus a minimization of
possible fault points. Connections between two circuits (printed boards) are
always direct.
The standardization of the cables has
enabled simplifications in documentation, production and testing. To a great
extent prefabricated cables can be
used, factory-produced, delivered complete and tested on site.
There are four main types of cable:
n
signal cable
•
signal cable with test facility
•
bus cable
•
power distribution cable
Figs. 12 and 13 show examples of different cables.
106
All cables connected from front
All cables are connected from the
front of the row to board front connectors or to a connection field in the
wiring unit. In this way existing cables
may be changed or new cables added
and additional equipment is easy to install. The front connection also aids
operation and maintenance work, as it
is easy to connect test equipment and
instruments, fig. 14.
The earthing system has, where possible, been incorporated in the structure to ensure perfect exchange earthing. The distribution system has socalled dynamic earthing, using an
earth lead parallel to the power lead.
This provides an equalizing effect on
the occasional transients2.
Decentralized power distribution
The voltages necessary to drive the
electronics are produced locally in
the respective magazines. This structure forms part of the reliability strategy of the systems. Power is provided
by DC/DC converters; normally these
are not duplicated, fig. 15.
packing density, however, heat dissipation often sets a limit to packing.
Good heat dissipation properties
Component minimization enables high
Fig. 14
Front connection. Cables connected to PC
board fronts and to wiring unit
Fig. 15
Decentralized power distribution. 50 W
converter in magazine
The largest, 200 W, converter forms a
unit, which is handled as a magazine,
fig. 16.
In normal conditions the AXE system
requires no forced air cooling. The
heated air which is funnelled up
through the structure should be removed from the switchroom by extraction ventilators, fig. 17.
In severe climatic conditions air coolinn and fans mav be installed.
107
Technical data
UNITS OF MEASURE
Basic unit:
1 M = 2.54 mm (M = Module)
Building module: 1 BM = 16 M = 40.64 mm
ROW STRUCTURE MECHANICS BYB 101
Height:
2250 mm (6 shelves) or
2900 mm (8 shelves)
Depth:
Single row: 360 mm
Double row: 620 mm
Shelf section width: 18 BM (731.52 mm)
24 BM (975.36 mm)
Cable section width: 3 BM (121.92 mm)
6 BM (243.84 mm)
Fig. 16
DC/DC converters. There are different sizes
for 200 W, 50 W and 20 W. Floating output is used
so that negative as well as positive voltages
can be produced
MAGAZINE BFD 111—129
Height: 6 BM (243.84 mm)
Width: N X 3 B M , where N = 1 , 2 , 3 . . . 8
Depth: 220 mm
Board spacing: 6 M (15.24 mm) or 8 M (20.32 mm)
Number of PC boards: From 6 up to 62 PCB
assemblies of type ROF13
* Only for centralprocessor unit APZ 210
** Only as daughter-board for joint printed
board
CONNECTOR
According to IEC Draft 48 B (Germany) 53
Standard 32 pins, pin spacing 2 X 2 M
Special 48 pins, pin spacing 1 X2 M
References
1.
Fig. 17
Parallel air cooling through free convection
Sorme, K. and Jonsson, I.: AXE —
a functionally modular SPC system. ISS 74 — 411/1—7.
2. Orevik, A.: Power supplies for
electronic telephone exchanges.
Ericsson Review 57 (1974): 4, pp
120—127.
The Ericsson Group
SM
With associated companies and representatives
EUROPE
SWEDEN
Stockholm
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Alingsas
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OMAN
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Representatives In:
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1. Sales company w i t h manufacturing
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TELEFONAKTIEBOLAGET LM ERICSSON
LJUNGLOFS. STHLM 1976

AXE 10 - System Description

Transcription

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