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ERICSSON<br />
REVIEW<br />
1 1978<br />
OPERATIONAL EXPERIENCE FROM AXE 10 IN SODERTALJE<br />
A NEW INTERNATIONAL EXCHANGE IN KUWAIT<br />
STORED PROGRAM CONTROLLED PABX, ASB 100<br />
FIELD TRIAL WITH COMMON CHANNEL SIGNALLING<br />
60 MHZ COAXIAL CABLE SYSTEM FOR 10800 CHANNELS<br />
DO THE MEDIA UNDERSTAND TELECOMMUNICATIONS
ERICSSON REVIEW<br />
Vol.55, 1978<br />
Contents<br />
Display Systems<br />
Page<br />
Colour Display System SEMIGRAF 240 86<br />
Electronic Equipment for Defence Applications<br />
Laser Activities at LM Ericsson 66<br />
Satellite Communication using a Multi-Beam Array 126<br />
Operation and Maintenance<br />
Operational Experience from AXE 10 in Sodertalje 2<br />
Operational Experience from the Mollison International<br />
Switching Centre in London 58<br />
Operational Experience of ANA 30 in Arhus 92<br />
AXB 20 - Operation and Maintenance Characteristics 106<br />
Power Supply Systems<br />
A New Generation of Power Supply Equipment, Type BZD 112 46<br />
Private Exchanges<br />
Stored Program Controlled PABX, ASB 100 11<br />
Telephone Exchange Systems<br />
A New International Exchange in Kuwait 8<br />
Field Trial with Common Channel Signalling 20<br />
Saudi Arabia-the Largest Telephone Project in the World 42<br />
History of Local Telephone Switching in Australia<br />
and Background to the AXE Decision 114<br />
New Generation of Ringing and Tone Signalling Equipments, BKL 600 130<br />
Digital Group Selector in the AXE system 140<br />
AXE 10 with Digital Group Selector in the Telephone Network 150<br />
Transmission Technique<br />
60 MHZ Coaxial Cable System for 10800 Channels 28<br />
Digital Multiplex Equipment for 8 and 34 Mbit/s Line Systems 76<br />
New Generation of 120 and 480-Channel FDM Systems<br />
for Two-Wire Cable Operation 96<br />
Miscellaneous<br />
Do the Media Understand Tele<strong>com</strong>munications 38<br />
COPYRIGHT T E LEFON AKTI E BOL AG ET LM ERICSSON STOCKHOLM SWEDEN 1978
ERICSSON REVIEW<br />
NUMBER 1 • 1978 • VOLUME 55<br />
Copyright Telefonaktiebolaget LM Ericsson<br />
Printed in Sweden, Stockholm 1978<br />
RESPONSIBLE PUBLISHER DR. TECHN. CHRISTIAN<br />
JACOB/EUS<br />
EDITOR GUSTAF O<br />
DOUGLAS<br />
EDITORIAL STAFF FOLKE<br />
BERG<br />
EDITOR'S OFFICE S-126 25<br />
STOCKHOLM<br />
SUBSCRIPTION ONE YEAR $6.00 ONE COPY $1.70<br />
PUBLISHED IN SWEDISH, ENGLISH, FRENCH AND<br />
SPANISH<br />
Contents<br />
2<br />
8<br />
11<br />
20<br />
28<br />
38<br />
Operational Experience from AXE 10 in Sodertalje<br />
A New International Exchange in Kuwait<br />
Stored Program Controlled PABX, ASB 100<br />
Field Trial with Common Channel Signalling<br />
60 MHZ Coaxial Cable System for 10800 Channels<br />
Do the Media Understand Tele<strong>com</strong>munications<br />
COVER<br />
Line repeater for 60 MHZ coaxial cable system for<br />
10 800 channels
Operational Experience from AXE 10<br />
in Sodertalje<br />
Sten Rimbleus<br />
The Swedish Tele<strong>com</strong>munications Administration has operational experience of<br />
SPC exchanges which goes back to 1968, when the first AKE 12 exchange was<br />
put into operation in Tumba near Stockholm. Since then a total of three AKE 13<br />
exchanges have been installed in Stockholm and Gothenburg. The operational<br />
experience from these has been good, as has been reported in previous articles in<br />
Ericsson Review* ~ 3 . The present article describes the Swedish Tele<strong>com</strong>munications<br />
Administration's field trial and eight months' operational experience from a new<br />
generation of SPC exchanges, namely from the first AXE 10 exchange in Sodertalje.<br />
The installation has already been described in a previous issue of Ericsson<br />
Review 4 .<br />
UDC 621.395.722<br />
681.3.065<br />
The Sodertalje exchange<br />
Sodertalje is the zone centre for the Sodertalje<br />
trunk code area. A number of<br />
group centres and terminal exchanges<br />
are connected to the exchange. There<br />
are direct routes to Stockholm and nearby<br />
smaller <strong>com</strong>munities and to a number<br />
of other cities in the country, of<br />
which Gothenburg and Malmo are the<br />
largest, fig. 1.<br />
On March 1st, 1977 the new 3000-line<br />
AXE 10 exchange in Sodertalje was taken<br />
into service. It then took over the<br />
corresponding number of lines from the<br />
existing AGF exchange, which served<br />
approximately 32 000 subscribers. This<br />
was the first step in a successive replacement<br />
of the AGF exchange (500-<br />
line selectors) by AXE 10.<br />
The new exchange was put into service<br />
with close cooperation between manufacturer<br />
and customer, which has to a<br />
great extent contributed to a successful<br />
result.<br />
The Tele<strong>com</strong>munications<br />
Administration's field trial<br />
Objectives<br />
Before the AXE 10 exchange was put<br />
into operation the Administration's staff<br />
carried out a 2-week continuous field<br />
trial in order to check<br />
Fig. 1<br />
Sodertalje trunk code area with some of the<br />
larger routes<br />
— Route<br />
^ ^ High usage route
3<br />
STEN RIMBLEUS<br />
Stockholm Tele<strong>com</strong>munication Area<br />
Swedish Tele<strong>com</strong>munications Administration<br />
Fig. 2<br />
The brochure distributed by the Swedish Tele<strong>com</strong>munications<br />
Administration when the AXE<br />
exchange was to be put in service<br />
The Swedish telephone network is to undergo a considerable<br />
renovation The telephone exchanges will therefore<br />
be replaced by new, <strong>com</strong>puter-controlled exchanges<br />
that will permit a large number of new tele<strong>com</strong>munication<br />
facilities for the subscribers in the future.<br />
The work will start here in Sodertalje on March 1st this<br />
year, when approximately 3000 telephones in the number<br />
series 30 000 - 32 999 will be switched over to a <strong>com</strong>putercontrolled<br />
telephone exchange AH the changeover work<br />
will be carried out at the telephone exchange, and it will<br />
not be necessary to change your telephone set<br />
The new tele<strong>com</strong>munication facilities will be introduced<br />
gradually and the immediate changes will be that<br />
• the dialling tone <strong>com</strong>es quicker<br />
D the pitch of the signal is changed<br />
• the ringing signal <strong>com</strong>es every 6th second instead of<br />
every 10th<br />
• the reference tone is changed to a triad<br />
The next stage of the modernisation program is planned<br />
for the second half of 1978 All telephones in Sddertalie<br />
with numbers that start with 1. 3, 6 or 8 will be connected<br />
to the new telephone exchange in 2-3 years At that time<br />
it will also be possible to obtain all the new tele<strong>com</strong>munication<br />
facilities.<br />
We will be contacting you again later on and we will then<br />
be explaining what these facilities are and how they<br />
function.<br />
THE TELECOMMUNICATIONS ADMINISTRATION<br />
Sodertalje<br />
— that the operational reliability of the<br />
exchange met the set requirements<br />
— that the traffic with interworking exchanges<br />
functioned satisfactorily<br />
— that the operating instructions provided<br />
took into account all the operating<br />
routines<br />
— that in other respects the exchange<br />
was ready to be taken into service.<br />
Execution<br />
The field trial started with the loading<br />
of the exchange and subscriber data required<br />
for operation. The exchange was<br />
loaded with internal traffic as well as<br />
traffic to and from interworking exchanges.<br />
It was considered as being in<br />
service, and thus all handling was done<br />
in accordance with the applicable operating<br />
and maintenance routines.<br />
The field trial <strong>com</strong>prised some 30 different<br />
activities, which were carried out<br />
mainly during the daytime. During the<br />
night the exchange was unmanned,<br />
with the remote alarm system connected<br />
to the Stockholm maintenance<br />
centre.<br />
Some of the most interesting trial activities<br />
were:<br />
a. Supervision of test traffic. This <strong>com</strong>prised<br />
the reading or checking of<br />
— the counter for the subscriber traffic<br />
generator<br />
— call connections<br />
— the results of the weekend tests<br />
described below<br />
— the results of the supervisory tests<br />
that were carried out<br />
— fault printouts (that they were obtained).<br />
It also included keeping a journal of<br />
fault printouts and any measures required<br />
to correct faults.<br />
b. Weekend tests, an unmanned longterm<br />
test that was started on the Friday<br />
evening and finished Monday<br />
morning. Test traffic, traffic recording<br />
and supervision functions were<br />
connected in during this test.<br />
c. Traffic recording for verifying the test<br />
traffic and traffic recording functions<br />
d. Alarm and alarm transmission for<br />
checking local alarm functions and<br />
the transmission of alarms to a superior<br />
centre.<br />
e. Regular charging output for checking<br />
that the charging was correct.<br />
f. Fault diagnosing, repair and repair<br />
checking in connection with the simulation<br />
of<br />
— permanent faults in the synchronously<br />
duplicated central processor<br />
— permanent faults in the current<br />
feeding<br />
— permanent faults in memories<br />
— temporary faults in various devices.<br />
Activity f. <strong>com</strong>prised checking that the<br />
automatic fault analysis functioned<br />
properly by giving the expected fault<br />
printouts, and also that the operating<br />
instructions were adequate. The faults<br />
that were detected during the various<br />
stages of the field trial were corrected<br />
as they arose.<br />
Result<br />
The faults were recorded in a journal<br />
and divided into categories, such as service<br />
quality, system restart and breakdown.<br />
The Tele<strong>com</strong>munications Administration<br />
had set requirements for each<br />
category in the form of the maximum<br />
number of permitted faults or maximum<br />
loss of traffic. The test showed that<br />
these requirements were met with a<br />
good margin, and as a result it was decided<br />
to put the AXE 10 exchange into<br />
service on March 1 st, 1977 at 4 a.m.<br />
Putting into service and<br />
subcriber reactions<br />
When the exchange was put into service,<br />
3000 subscriber lines from the<br />
AGF exchange were connected in. The<br />
number series in question included<br />
2430 ordinary subscriptions and also<br />
PABXsubscribersandthree-coin instruments.<br />
Before the exchange was put into service<br />
all subscribers had received a leaflet<br />
from the Administration's Sales Department<br />
with diverse information concerning<br />
the changeover, fig. 2.<br />
The changeover was planned down to<br />
the last detail. Naturally the morning
4<br />
with its heavy traffic load was awaited<br />
with great suspense. Incidentally, some<br />
fifty representatives of LM Ericsson,<br />
ELLEMTEL and the Swedish Tele<strong>com</strong>munications<br />
Administration were present<br />
for this historical event.<br />
The traffic recordings showed a successive<br />
increase in traffic volume and fault<br />
<strong>com</strong>plaints started to <strong>com</strong>e in. The necessary<br />
corrections were carried out as<br />
the faults appeared. The total number<br />
of fault <strong>com</strong>plaints was about 100 during<br />
the first day, 20 during the second<br />
day and 10 during the third day. The<br />
types of faults that occurred and the<br />
reactions of the subscribers are given<br />
in a summary on the last page of this<br />
article.<br />
Operating statistics<br />
When introducing a new system it is important<br />
to obtain confirmation that the<br />
system really meets all the requirements<br />
laid down in the design guidelines. A<br />
thorough follow-up of the first exchange,<br />
including the rectifying of any deficiencies<br />
in design and handling, simplifies<br />
the work on subsequent exchanges<br />
very considerably.<br />
The built-in supervisory functions of<br />
AXE 10 have been an excellent aid in<br />
this respect. These functions have been<br />
supplemented with traffic route testers,<br />
for checking the operational reliability,<br />
and detailed operating statistics in<br />
which all faults and deficiencies as re-<br />
gards function and handling are entered.<br />
Operational reliability<br />
Test traffic was generated by the traffic<br />
route testers and the results show a<br />
successively increasing operational reliability.<br />
The loss of internal traffic during<br />
the first month was 0.9%, but after<br />
four months of operation the loss had<br />
fallen to as low as 0.03 %.<br />
Traffic recordings<br />
The system includes flexible functions<br />
that are of great value for traffic recording<br />
purposes. The traffic has therefore<br />
been followed up regularly by means of<br />
traffic recordings, the results of which<br />
have been analysed. For example, the<br />
congestion on one junction route occasionally<br />
amounted to 3 — 4 %. The route<br />
has since been enlarged and an extract<br />
from the traffic recording results for October<br />
is given in fig. 3.<br />
Hardware faults<br />
Only one design fault has been found,<br />
see item 1 in the summary. A number of<br />
printed board assemblies with faulty<br />
<strong>com</strong>ponents have also been localized<br />
and replaced.<br />
Software corrections<br />
A number of program corrections were<br />
carried out during the first five months<br />
in service. Five cases were caused by<br />
incorrectly specified time limits and<br />
were cleared on the very first day of<br />
operation. Ten other faults have dis-<br />
SDT*AXE*1 0225 TW1 TIME 771010 1001 PAGE 1<br />
TRAFFIC RECORDING RESULTS 00<br />
TRG RBNR NRP RPL PRE<br />
1 2 1 12 1<br />
Fig. 3<br />
The result ot a one-hour traffic recording in<br />
October 1977<br />
TRG Traffic recording group number<br />
RBNR Recording batch number<br />
NRP Number of recording periods<br />
RPL Recording period length (Number of basic<br />
recording periods)<br />
RPERN Recording period number<br />
R Symbolic route number<br />
TRAFFIC Traffic flow In erlangs<br />
CALLS Number of calls<br />
CONG Call congestion as a percentage<br />
NDV Number of devlces/llnes/llnks connected In<br />
NBL01 Number of blocked devlces/llnes/links at the<br />
start of a recording period<br />
NBL02 Number of blocked devlces/llnes/links at the<br />
end of a recording period<br />
DATE Date<br />
TIME Time<br />
• High usage routes
Fig. 4 (left)<br />
The operation and maintenance manual, <strong>com</strong>prising<br />
ten binders<br />
Fig. 5 (right)<br />
Tape cassette, to which the central processor<br />
feeds out information regarding subscriber call<br />
markings. One cassette holds the information for<br />
all subscribers in the exchange<br />
Fig. 6<br />
Control room.<br />
The staff in the control room have access to, for<br />
example, typewriters, displays, alarm panels and<br />
tape cassettes, and with the aid of these they can<br />
receive and feed in information to the AXE<br />
exchange. Some examples of received information<br />
are alarms, fault indications and traffic recording<br />
information. The information fed in to the<br />
exchange can concern, for example, traffic<br />
routing, special subscriber facilities such as<br />
abbreviated dialling, the tracing of calls and<br />
charging checks.<br />
Fig. 7 (left)<br />
Switch room.<br />
The printed board assemblies for the exchange<br />
equipment are mounted in magazines which are<br />
placed in shelves. The shelves are covered with<br />
protective plates. The shelves and plates are<br />
finished in a grey colour, which together with<br />
warm colours on walls and ceiling give the switch<br />
room a quiet and <strong>com</strong>fortable appearance<br />
Fig. 8 (right)<br />
Typewriter terminal.<br />
The man-machine <strong>com</strong>munication takes place via<br />
such aids as typewriters. The typewriter is a quiet<br />
matrix printer.<br />
Fig. 9<br />
Floor plan for the AXE 10 equipment for a total of<br />
12000 lines. The rows marked in red serve the<br />
3000 lines already in operation. The rows take up<br />
only 1/3 of the space of the corresponding<br />
500-line selector racks<br />
TSS Signalling subsystem (or outgoing and In<strong>com</strong>ing<br />
lines<br />
GSS Group selector subsystem<br />
SSS Subscriber subsystem<br />
CPS Central processor subsystem<br />
IOS Input/output subsystem
Fig. 10a<br />
Minor automatic system restarts. Often caused<br />
by software faults. Takes 3 seconds. Established<br />
calls are not affected<br />
Fig. 10b<br />
Major automatic system restarts<br />
• Often caused by software faults. Takes 3 seconds.<br />
Established calls are disconnected<br />
Includes reloading. Caused by software faults alone or<br />
In <strong>com</strong>bination with hardware faults. Takes 7 minutes<br />
All traffic handling stops<br />
March May July Sept Time<br />
April June Aug Oct<br />
Fig. 10c<br />
Manually initiated system restarts<br />
• Minor restarts caused by software faults that have led<br />
to the holding of a switch, other devices or individual<br />
subscribers<br />
Ma|or restarts caused by software faults that have led<br />
to major traffic disturbances<br />
turbed the traffic in one way or another,<br />
whereas the remaining 35 faults during<br />
the five-month period consisted mainly<br />
of small adjustments intended to improve<br />
the handling characteristics.<br />
Thanks to the modular structure and design<br />
of the software it has been easy to<br />
make corrections. These have always<br />
been carried out by the designer concerned<br />
and verified in the system test<br />
equipment before being introduced in<br />
Sodertalje.<br />
System restart<br />
The system automatically carries out a<br />
system restart when implausible data<br />
are detected or there is an error in the<br />
program handling sequence. Restart<br />
can also be ordered manually by the<br />
operator. This function is an excellent<br />
means of maintaining the operational<br />
readability of the system since it limits<br />
the effects of a serious fault. In addition<br />
an informative printout is obtained in<br />
connection with the restart, which gives<br />
the designer the necessary basic data<br />
for carrying out corrections.<br />
Figs. 10 a—c show the frequency of the<br />
various types of restarts since the exchange<br />
was put into operation. Most of<br />
the necessary software corrections had<br />
been carried out by August 1977, so that<br />
for example the number of manual restarts<br />
had decreased considerably by<br />
then. It should also be pointed out that<br />
major system restarts were partly caused<br />
by incorrect handling.<br />
System stop<br />
The only system stop that has occurred<br />
so far took place after 10 days in service<br />
and lasted approximately 15 minutes. It<br />
was caused by a <strong>com</strong>bination of software<br />
and hardware faults, a type of fault<br />
which, as is well known, is most difficult<br />
to foresee.<br />
Operation and maintenance<br />
routines<br />
Manning<br />
The AXE exchange was manned day and<br />
night during the first week in service and<br />
thereafter only during normal working<br />
hours (Monday-Friday 7.30 a.m. to 4<br />
p.m.).<br />
The Tele<strong>com</strong>munications Administration,<br />
who have responsibility for the<br />
operation, now have two operators stationed<br />
in the exchange. Their main task<br />
is to carry out the normal operation and<br />
maintenance activities.<br />
Administrative staff have also been stationed<br />
temporarily in the exchange in<br />
order to follow events there and to further<br />
develop the operation and maintenance<br />
routines. Installation staff from<br />
LM Ericsson and some designers from<br />
ELLEMTEL acted as advisors during the<br />
first two months.<br />
As this was the first AXE 10 exchange<br />
the Tele<strong>com</strong>munications Administration<br />
wanted to guard against unforeseen<br />
events. For this purpose an expert group<br />
was appointed, where each member was<br />
a specialist in his own field. The members<br />
worked as usual, but could be contacted<br />
at any time of the day or night.<br />
By the end of October the Stockholm<br />
maintenance centre had received a total<br />
of eight alarms during night-time which<br />
were serious enough to necessitate<br />
sending out an operator to the exchange.<br />
It was possible to clear all these<br />
faults with the aid of the existing operating<br />
instructions without having to call<br />
in the expert group.<br />
Documentation<br />
The most important documents are included<br />
in the operation and maintenance<br />
manual, which <strong>com</strong>prises operating<br />
instructions stating what is to be<br />
done, step by step, in different situations.<br />
The instructions are arranged per<br />
activity and also contain descriptions<br />
of <strong>com</strong>mands and printouts. The operation<br />
and maintenance manual consists<br />
of ten binders, which cover the information<br />
needs for all activities. It was found<br />
that with the aid of this manual the Administration's<br />
operators were able to<br />
carry out, on their own, fairly <strong>com</strong>plicated<br />
repairs, such as changing printed<br />
board assemblies in the data processing<br />
system, without causing operational<br />
disturbances.<br />
It is expected that only this manual will<br />
be needed in future AXE exchanges. As<br />
Sodertalje was the very first AXE 10 exchange<br />
it was also provided with system<br />
descriptions and program and hardware<br />
documentation.
Types of faults, measures and<br />
subscriber reactions<br />
Of the fault types and subscriber reactions given<br />
below, only type 1 represents a real fault. The<br />
other types are to be considered as mishaps<br />
and are difficult to foresee. Moreover, experience<br />
has shown that they usually do not appear<br />
until an SPC exchange operates in its proper<br />
environment.<br />
1. Traffic to certains PABXs did not function<br />
satisfactorily because of faulty system adaption,<br />
which in its turn was caused by ambiguities<br />
in the specifications. The fault was<br />
cleared immediately by means of a hardware<br />
correction.<br />
2. Unforeseen variations in different AGF equipments<br />
caused such faults as failure to establish<br />
speech connection, prematurely disconnected<br />
calls and holding. The faults were<br />
cleared by changing the time-dependent signals<br />
to and from AXE 10.<br />
3. Certain number series to other trunk code<br />
areas were erroneously barred and were<br />
opened by means of a correction of the exchange<br />
data.<br />
4. Missing data for a number of subscribers<br />
were included.<br />
5. A number of faulty subscriber connections<br />
in the main distribution frame were corrected.<br />
6. The built-in line test function was set to the<br />
prescribed limits, but these proved to be too<br />
narrow in view of the condition of the network.<br />
Many subscribers were temporarily<br />
blocked and the values for the line test function<br />
were adjusted to suit the actual network<br />
conditions.<br />
7. Because of the very short setting-up time in<br />
AXE 10 unwarranted fault <strong>com</strong>plaints concerning<br />
"permanent dialling tone" were received,<br />
since this tone is sent out immediately<br />
the subscriber lifts the receiver or dials<br />
a trunk code.<br />
8. An individual supervisory function indicated<br />
that for 24 hours no call had been initiated<br />
from a three-coin instrument situated<br />
in a lonely place. Since the telephone turned<br />
out to be in working order it is likely that it<br />
had not been used during that period. The<br />
supervisory interval was therefore extended<br />
to 48 hours, and since then there has been<br />
no more indications.<br />
Plans for the future<br />
The experience gained from the Sodertalje<br />
exchange has helped to make possible<br />
the realization of previously prepared<br />
plans for the future earlier than<br />
expected.<br />
Extension rate<br />
The Tele<strong>com</strong>munications Administration's<br />
network now contains about 5<br />
million installed local lines, of which<br />
just over half are served by modern<br />
crossbar exchanges. The remainder are<br />
connected to AGF exchanges, the oldest<br />
of which have been in service for<br />
over 50 years. Problems concerning the<br />
realization of new functions, wear,<br />
spares and maintenance have led to the<br />
Administration preparing a modernisation<br />
plan. It <strong>com</strong>prises a long-term program<br />
for the replacement of AGF by<br />
AXE 10, with the aim that all AGF exchanges<br />
shall be replaced before the<br />
year 2000.<br />
Centrally stationed staff<br />
It is already clear that a changeover to<br />
AXE 10 will mean a radical improvement<br />
in the operation and maintenance activities.<br />
Thus the system permits authorized<br />
departments within the Administration<br />
to send <strong>com</strong>mands via terminals<br />
(I/O devices) direct to the exchanges<br />
concerned, in order to carry out any desired<br />
changes. For example, the sales<br />
department will be able to connect in or<br />
disconnect subscribers direct by means<br />
of a <strong>com</strong>mand, instead of having to<br />
make out a work order and sending it<br />
to the exchange for manual action. This<br />
applies for most other operational activities<br />
that can be remotely controlled,<br />
for example<br />
— connecting in and disconnecting different<br />
subscriber facilities<br />
— traffic recording<br />
- traffic observation<br />
- reading of call meters<br />
— changing the charging and traffic<br />
routing<br />
- collecting statistics<br />
It is the aim of the Tele<strong>com</strong>munications<br />
Administration to successively transfer<br />
all operational and maintenance work<br />
within a geographical area to staff stationed<br />
at a centrally placed maintenance<br />
centre. From there the maintenance<br />
staff will be sent out to the exchanges<br />
when the need for manual intervention<br />
arises.<br />
Conclusion<br />
The operational experience obtained<br />
from the Sodertalje exchange has<br />
proved that the modular structure of<br />
both the system software and hardware<br />
makes the system easy to handle.<br />
Furthermore owing to the fact that the<br />
operational reliability already from the<br />
beginning has proved to be good it has<br />
been possible to introduce push-button<br />
dialling and abbreviated dialling six<br />
months earlier than was originally planned.<br />
If regard is also paid to the wide range<br />
of possibilities and facilities offered by<br />
AXE 10 —not least concerning rationalization<br />
and reducing the cost of the operation<br />
and maintenance activities —it is<br />
clear that this new generation of SPC<br />
exchanges meets the requirements of<br />
today and tomorrow and has thus <strong>com</strong>e<br />
to stay.<br />
7<br />
References<br />
LSundblad, A.: Operating Experience<br />
from AKE 120, Tumba. Ericsson<br />
Rev. 47 (1970):2, pp. 42-49.<br />
2. Ericsson, L. G. and Persson, A.:<br />
Operation and Maintenance Characteristics<br />
of AKE 13. Ericsson<br />
Rev. 54 (1977):3, pp.125-135.<br />
3. Ericsson, L. G. and Persson, A.:<br />
Operational Experience of AKE 13.<br />
Ericsson Rev. 54 (1977):4, pp.168<br />
-173.<br />
4. Meurling, J.: Sodertalje-the First<br />
AXE Exchange. Ericsson Rev. 54<br />
(1977):1,pp. 2-6.
A New International Exchange<br />
in Kuwait<br />
Abdullah Al-Sabej<br />
On August 75,7977, the subscribers in Kuwait were given the possibility of dialling<br />
automatic international calls. On this date, a new international SPC exchange was<br />
put into operation. This exchange was the first of the LM Ericsson system ARE 13<br />
with the processor system ANA 30.<br />
The ARE 13 system has previously been described in a serie of articles in Ericsson<br />
Review^3.<br />
This article will therefore only briefly describe the functions that are<br />
characteristic of the exchange in Kuwait as well as the experiences gained from the<br />
installation and putting into service of the exchange.<br />
UDC 621.395.722:<br />
681.3.065<br />
Fig. 1<br />
Street scene from Kuwait. The tall building in the<br />
background is the telephone exchange<br />
A smaller international exchange of<br />
non-LM Ericsson design for operator<br />
assisted traffic was already in operation<br />
in Kuwait, but due to the demand for a<br />
larger system to handle international<br />
subscriber dialled traffic, the Ministry of<br />
Communications announced a public<br />
tender in 1975. After studies of various<br />
bids, the Ministry selected the ARE 13<br />
system from LM Ericsson. Among the<br />
features of the ARE 13 system that received<br />
most consideration, were:<br />
— The large line capacity and traffic<br />
handling capability of the system, up<br />
to 24 000 multiple positions (triple<br />
exchange) and 300 000 calls per hour.<br />
The modularity of the system makes it<br />
possible to extend it economically in<br />
order to meet the dramatically increasing<br />
international traffic demand<br />
in Kuwait.<br />
— The advanced operator and charging<br />
facilities with toll-ticketing, TT.<br />
— The modular and standardized design<br />
of both software and hardware,<br />
which provides high reliability and<br />
easy handling.<br />
Installation in two phases<br />
In accordance with the contract the first<br />
phase of the ARE 13 exchange with about<br />
650 international circuits should be<br />
taken into service on 30.11.1977. However,<br />
through the <strong>com</strong>bined efforts of all<br />
parties concerned, it was possible to<br />
take the ARE 13 into service on
9<br />
ABDULLAH AL-SABEJ<br />
Chief Engineer<br />
Ministry of Communications, Kuwait<br />
Fig. 2<br />
Some of the most important functions of the<br />
international exchange in Kuwait<br />
15.8.1977. Previously an ARM exchange<br />
with operator handled traffic containing<br />
150 international circuits was, however,<br />
installed in order to meet the increasing<br />
demand in a temporary way. This ARM<br />
exchange was taken into service on<br />
1.10.1976.<br />
The second phase of the contract involves<br />
extension of the ARE 13 exchange<br />
and conversion of the interim<br />
ARM exchange to ARE 13. Thus ARE 13<br />
will be extended to 1400 international<br />
circuits and 120 operator positions. The<br />
installation of this second phase will<br />
take place during 1978.<br />
A modern international maintenance<br />
centre was also included in the contract<br />
and was taken into service in connection<br />
with the first phase of ARE 13.<br />
The telephone network<br />
of Kuwait<br />
Kuwait has a very modern and well developed<br />
telephone network. The local<br />
exchanges are mainly ARF 102, none of<br />
which are older than 10 years. SPC<br />
technology is also now being introduced<br />
in the local network in the form of<br />
ARE 11 and AXE 10. There are also a few<br />
exchanges of non-LM Ericsson systems,<br />
with which ARE 13 is interworking.<br />
Due to the geography of the country, no<br />
4-wire transit exchanges are necessary<br />
on the national level. Accordingly, only<br />
2-wire tandem stages are used for the<br />
national traffic.<br />
The local exchanges are thus connected<br />
to the ARE 13 either direct or via the<br />
tandem stages.<br />
As is shown in fig. 2 the international<br />
ARE 13 exchange connects Kuwait to<br />
the rest of the world via the following<br />
media:<br />
- Satellite connections both via the<br />
Atlantic and the Indian Ocean satellites<br />
with signalling system CCITT No.<br />
5<br />
- Coaxial cable and radio link connections<br />
to neighbouring countries, with<br />
signalling system CCITT R2.<br />
- A small number of manual connections<br />
with signalling system CCITT<br />
No. 1.<br />
Some important features<br />
of ARE 13<br />
ARE 13 is built up of a switching part,<br />
with the well proven LM Ericsson cross-
10<br />
bar switch, and a control part with the<br />
reliable and easy-to-handle processor<br />
system ANA 30.<br />
The ARE 13 in Kuwait <strong>com</strong>prises<br />
approximately 300 electronic shelves<br />
and 11000 printed circuit boards.<br />
The new operator and TT system includes<br />
a number of features of importance<br />
to the Ministry. These systems<br />
have previously been described in<br />
Ericsson Review 3 .<br />
The operator system considerably improves<br />
the service for semi-automatic<br />
calls by the provision of on-demand<br />
service and automatic TT-charging. Automatic<br />
print-out of information concerning<br />
delay calls, immediate price<br />
advice and international conference<br />
calls are examples of other services that<br />
the ARE 13 in Kuwait provides.<br />
The TT-charging system utilizes the<br />
same hardware in the processors as<br />
ANA30. In this system, the price information<br />
is automatically calculated for<br />
all calls —automatic, as well as operator<br />
assisted —and the result is stored on<br />
magnetic tapes. Consequently, this TTsystem<br />
considerably reduces the Ministry's<br />
billing work.<br />
Installing and Testing<br />
The installation has been carried out by<br />
the Ministry with minimal supervision<br />
from LM Ericsson. This has been possible<br />
due to the familiarity of the Ministry's<br />
staff with the technique of the switching<br />
part (similar to ARF 102) and the efficient<br />
training programmes conducted.<br />
The procedure adopted for this first ARE<br />
exchange in Kuwait has resulted in reduced<br />
installation costs and thorough<br />
practical experience for the Ministry's<br />
staff.<br />
The staff are therefore well prepared for<br />
the operation and maintenance of this<br />
exchange, and furthermore, also for<br />
forth<strong>com</strong>ing installation, testing and<br />
operation of the contracted ARE 11 exchanges.<br />
Operational Experience<br />
Despite the fact that the installation and<br />
testing time of the exchange were considerably<br />
shortened, this world premier<br />
ARE 13 exchange was put into service<br />
with favourable result.<br />
Fig. 3<br />
International maintenance centre<br />
References<br />
1. Andersson, B. et al.: ARE Systems<br />
in Modern Networks. Ericsson Rev.<br />
54 (1977):2, pp. 54-66.<br />
2. Hemre, A. and Hagard, G.: The<br />
Software and Its Handling in ARE<br />
Systems. Ericsson Rev. 54 (1377):2,<br />
pp. 77-85.<br />
3. Ellstam, S. and Olsson, B.: Stored<br />
Program Controlled Transit Exchange<br />
ARE 13 with Control<br />
System ANA 302. Ericsson Rev. 52<br />
(1975):3/4, pp. 116-127.<br />
4. Jansson, H. and Thune, U.: TT and<br />
Operator Systems for ARE 13.<br />
Ericsson Rev. 53 (1976):4, pp.<br />
184-193.
Stored Program Controlled<br />
PABX, ASB 100<br />
Per Furu<br />
In connection with the modernisation of their PBX range LM Ericsson, in cooperation<br />
with ELLEMTEL and the Swedish Tele<strong>com</strong>munications Administration,<br />
have developed an electronic, stored program controlled PABX for up to 100 extensions.<br />
The objectives of the development work were to develop an easy-to-handle<br />
system with the greatest number of functions that the economic aspects allowed.<br />
Special importance was attached to achieving a system that works with good<br />
economy during the whole of its life as regards operation, maintenance and<br />
administration.<br />
The operator's set has been given a new design in order to simplify the handling of<br />
calls. In addition to normal tasks the operator also has the possibility of carrying out<br />
a part of the administration and supervision of the PABX.<br />
UDC 621.395 24<br />
ASB 100 is a stored program controlled<br />
PABX system with the programs stored<br />
in a permanent semiconductor memory<br />
(PROM) and data stored in an electrically<br />
changeable semiconductor memory<br />
(RAM). The PABX is equipped with a<br />
single stage, non-blocking switching<br />
network with full accessibility between<br />
extensions and the devices that carry<br />
traffic.<br />
ASB 100 is available in two different<br />
cabinet heights depending on the final<br />
capacity required. The smaller cabinet<br />
can be built out to 40 extensions and the<br />
larger cabinet has a final capacity of 100<br />
extensions. The system has a high traffic<br />
handling capacity in both cases.<br />
The PABX is built up entirely of printed<br />
board assemblies, which are mounted in<br />
shelves in the cabinets. The wiring is<br />
carried out in a rear plane that is <strong>com</strong>mon<br />
for three shelves. The smaller<br />
system contains one such unit and the<br />
larger contains two. These units, and all<br />
external units, such as extensions and<br />
external lines, are interconnected by<br />
means of standardized cables equipped<br />
with plugs.<br />
The system can be delivered to the<br />
customers as a <strong>com</strong>plete, tested unit,<br />
which reduces the installation time considerably.<br />
Stored program control has made it<br />
possible to introduce a large number of<br />
new functions, which have previously<br />
been available only in large systems.<br />
The aim has been to provide these functions<br />
solely by additions to the software,<br />
as far as this is possible, and to avoid<br />
special equipments, wiring changes and<br />
special apparatus. However, space has<br />
been prepared in the rack for those<br />
functions that require extra equipment,<br />
and consequently a function can be introduced<br />
quite easily at any convenient<br />
time.<br />
The PABX permits any <strong>com</strong>bination of<br />
Fig. 1<br />
ASB 100. Operator's set and cabinet for 100 extensions
PER FURU<br />
Subscriber Equipment Division<br />
Telefonaktiebolaget LM Ericsson<br />
Fig. 2<br />
Block diagram for the stored program controlled<br />
PABX, ASB100<br />
rotary dial and push-button telephone<br />
instruments.<br />
The use of push-button telephone sets,<br />
which in addition to the ten digit buttons<br />
have buttons with the star and square<br />
symbols, makes it possible to provide<br />
such facilities as<br />
- individual abbreviated dialling<br />
- automatic call diversion<br />
- bypassing of automatic call diversion<br />
- direct switching to a loudspeaking<br />
telephone.<br />
The push-button telephone sets also<br />
have another button, the register button,<br />
for calling in a register, for example<br />
when making an inquiry call.<br />
Special importance has been attached<br />
to the utilization of the possibilities offered<br />
by a stored program controlled<br />
system as regards operation and maintenance<br />
and also administration. As regards<br />
operation and maintenance the<br />
aim has been to reduce the need for<br />
qualified staff and training to a minimum.<br />
This has been achieved through<br />
a well designed functional system structure<br />
in <strong>com</strong>bination with advanced test<br />
programs and easily understood documentation.<br />
The administration of the<br />
system has been made more efficient<br />
and flexible since certain tasks can now<br />
be allocated to the operator, and because<br />
it is possible to arrange central<br />
administration of several PABXs via the<br />
public telephone network.<br />
System design<br />
ASB 100 can be divided into a switching<br />
equipment and a control system. The<br />
exchange of information between these<br />
two takes place via a bus system. Fig. 2<br />
shows a block diagram of the system.<br />
The units shown in unbroken lines constitute<br />
the standard equipment in the<br />
exchange and the units shown in broken<br />
lines are supplementary equipments,<br />
which can be supplied if required.<br />
Switching equipment<br />
ASB 100 is equipped with an electronic<br />
switching network that is built up of<br />
thyristor crosspoints. This means that<br />
redirection in the switching network can<br />
be carried out very quickly and that the<br />
network can be used not only for speech<br />
<strong>com</strong>munication but also for the connection<br />
of different signalling units. Such<br />
units include the tone sender, which<br />
gives different types of tone information<br />
to the extension, or the dialling tone receiver,<br />
for receiving the dialling tone<br />
from the public network when this occurs.<br />
The use of a single-stage thyristor<br />
crosspoint switching network makes it<br />
possible to order the setting up of different<br />
connections direct from the units<br />
concerned, for example extension line<br />
circuit and tone sender, when initiating<br />
a call. Thus special circuits for setting<br />
up the switching network are not required.
13<br />
When the receiver is lifted the extension<br />
is connected to a tone sender that sends<br />
the dialling tone, after which dialling<br />
can start. If a conventional telephone set<br />
with a dial is used, the dialled digits are<br />
received direct in the extension line<br />
circuit, but if a telephone set equipped<br />
for tone frequency key sending is used,<br />
the digits are received by a push-button<br />
dialling tone receiver, which is connected<br />
to the tone sender. In both cases<br />
the digit information is transferred via<br />
the bus system to the control system for<br />
further analysis. If the digit analysis indicates<br />
that the call is internal, a connection<br />
is set up via a free local junctor<br />
trunk to the desired extension. If the call<br />
is external, a free line is connected up<br />
to a dialling tone receiver. Thus the extension<br />
is now connected to a tone<br />
sender and a trunk line to a dialling<br />
tone receiver.<br />
The external number can now be dialled<br />
and registered in the same way as in the<br />
case of an internal call.<br />
When the public exchange works with<br />
decadic impulsing the external number<br />
is transmitted with the aid of circuits in<br />
the trunk line circuit regardless of<br />
whether the extension has a telephone<br />
set with a dial or a push-button telephone<br />
set. The dialling tone receiver is<br />
disconnected when the dialling tone has<br />
been received. In cases where there is a<br />
second dialling tone the receiver remains<br />
connected until this tone has<br />
been received. The extension is connected<br />
to the external line when the dialling<br />
tone ceases. The tone sender is disconnected<br />
when the transmission of digits<br />
is <strong>com</strong>pleted.<br />
When an external call <strong>com</strong>es in, the<br />
trunk line is connected to the operator's<br />
console, after which the operator can<br />
dial the desired extension number and<br />
set up the call. A characteristic feature<br />
of ASB 100 is that the operator works<br />
with only one operator link. It is used<br />
only when the operator is actively engaged<br />
in any part of the call handling.<br />
Other functions, which concern the<br />
operator's work indirectly, such as ringing,<br />
camp on busy, parking etc., affect<br />
only the units concerned, for example<br />
external and extension lines, and are<br />
controlled <strong>com</strong>pletely from the central<br />
control system.<br />
Control system<br />
The control system in ASB 100 is built up<br />
around processor APN 163, developed<br />
by LM Ericsson, which is a powerful,<br />
general purpose 16-bit processor that is<br />
designed for a number of applications in<br />
different fields of activity.<br />
The choice of memories was based on a<br />
desire to obtain high flexibility at a low<br />
cost. For this reason permanent mem-<br />
Fig. 3<br />
Operator's set
Fig. 4<br />
The structure of the program system<br />
The cabinet on the left is<br />
for up to 100 extensions<br />
The cabinet on the right is<br />
for up to 40 extensions<br />
Fig. 5<br />
Cabinets for the exchange<br />
equipment<br />
ories (PROM) were chosen for storing<br />
the programs — program stores - whereas<br />
the parameters that can vary from<br />
one installation to another are stored in<br />
electrically changeable memories<br />
(RAM)-data stores. The latter also provide<br />
the storage capacity required for<br />
storing temporary data in connection<br />
with the traffic in progress in the PABX.<br />
The data store boards are equipped with<br />
chargeable miniature batteries that can<br />
keep the voltage intact for at least 100<br />
hours, so that the semi-permanent data<br />
stored in the data store will not be lost<br />
in case of a power failure.<br />
When designing the program system in<br />
ABS 100 the demands that can be made<br />
on a modern PABX have been met as far<br />
as possible. In addition to the abovementioned<br />
division into program and<br />
data stores it has been the aim to facilitate<br />
the introduction of new functions<br />
and make market adaptions. The<br />
structure of the program system is<br />
shown in fig. 4.<br />
The program system can be divided into<br />
three parts: traffic programs that handle<br />
the actual telephony functions, monitor<br />
programs that supervise the program<br />
handling and <strong>com</strong>mon functions in the<br />
exchange, and finally operation and<br />
maintenance programs.<br />
The traffic programs in their turn can be<br />
divided into two parts: one procedure<br />
block and one line signal block. The<br />
program modules of the procedure<br />
block each cover different traffic cases<br />
in the exchange, whereas the line signal<br />
block modules constitute the interface<br />
between the procedure programs and<br />
the different hardware units in the exchange.<br />
In this way small program modules with<br />
well defined interfaces have been<br />
obtained. The procedure program modules<br />
are affected when new facilities are<br />
introduced and existing ones are modified,<br />
and the line signal program modules<br />
are affected, for example, when the<br />
PABX is adapted to new types of signalling.<br />
Cabinets<br />
ASB 100 can be supplied with two different<br />
cabinet heights depending on the<br />
final capacity required, fig. 5. The smaller<br />
cabinet, which ac<strong>com</strong>modates one<br />
magazine containing three shelves,<br />
permits extension up to 40 extensions, 5<br />
local junctors, 12 trunk lines and 3 tone<br />
senders. The larger cabinet, which ac<strong>com</strong>modates<br />
two magazines with three<br />
shelves each, permits extension up to<br />
100 extensions, 10 local junctors, 24<br />
trunk lines and 6 tone senders. At the<br />
manufacturing stage space is prepared<br />
in the cabinets not only for the control<br />
unit and the required traffic-carrying<br />
devices and switches but also for the<br />
extra printed board assemblies that are<br />
required for additional facilities.<br />
There is also space in the cabinets for a<br />
built-in power unit.<br />
Switching network<br />
The switching network in ASB 100 is<br />
built up of thyristor crosspoint matrices<br />
for symmetrical two-wire through-connection.<br />
The matrix capacity gives<br />
optimum utilization with 40 and 100<br />
lines. A matrix, which is ac<strong>com</strong>modated<br />
on one printed board assembly, can<br />
connect 12 inputs to 28 outputs. Thus
15<br />
five such matrices permit connection of<br />
a total of 60 inputs. Of the 60 inputs, 40<br />
are used for connecting extensions<br />
while the others are reserved for connecting<br />
other units, for example<br />
operator and junction lines. The larger<br />
variant of ASB 100 has space for 20<br />
matrices, which provides the possibility<br />
of connecting 120 inputs to a maximum<br />
of 56 outputs.<br />
Traffic capacity<br />
Since ASB 100 is equipped with a nonblocking<br />
switching network its traffic<br />
capacity is determined entirely by the<br />
number of traffic-carrying devices. The<br />
system is dimensioned for a traffic volume<br />
of 0.17 erlangs per extension with a<br />
congestion of 0.01 and 20 — 40% internal<br />
traffic. This applies with the maximum<br />
number of extensions, 40 and 100<br />
respectively, connected. If a higher traffic<br />
capacity is required, this can easily<br />
be obtained by reducing the number of<br />
extensions. For example, a small system<br />
with 30 extensions connected can handle<br />
an average traffic of 0.23 erlangs per<br />
extension.<br />
Traffic facilities<br />
In stored program controlled systems it<br />
has not only been possible to introduce<br />
a large number of new facilities even in<br />
small exchanges, but also to administer<br />
the utilization of these facilities so that<br />
they can be used to the optimum extent.<br />
The various facilities have as far as possible<br />
been realized solely in software, in<br />
order to obtain greater flexibility and<br />
simpler administration. In this way it has<br />
been possible to eliminate rewiring and<br />
special apparatus.<br />
Basic facilities<br />
The basic equipment for the PABX includes<br />
three program store boards with<br />
a storage capacity of 8k words each.<br />
They contain the programs for all telephony<br />
functions offered by the exchange.<br />
The following functions are provided:<br />
— extension class of service allocation<br />
— internal calls<br />
— outgoing calls, direct or via the<br />
operator<br />
— in<strong>com</strong>ing calls via the operator<br />
— inquiry during internal as well as external<br />
calls<br />
— automatic transfer of internal as well<br />
as external calls<br />
— add on conference<br />
— call diversion to a <strong>com</strong>mon attendance<br />
point. This function can be<br />
ordered and cancelled from pushbutton<br />
telephones<br />
— priority<br />
— <strong>com</strong>mon or automatic night service<br />
connections<br />
— universal call back<br />
— flexible numbering<br />
— choice of individual trunk line (from<br />
the operator)<br />
— group hunting<br />
— direct call diversion to an individual<br />
attendance point. The function is<br />
programmed by the operator and is<br />
ordered or cancelled by extensions<br />
equipped with push-button sets<br />
— diversion to an individual attendance<br />
point if no answer is obtained<br />
— long distance traffic control<br />
— call pick-up<br />
— individual night service connection<br />
— transit traffic<br />
— <strong>com</strong>mon external abbreviated dialling<br />
Fig. 6<br />
The operator's console has symbols Instead of<br />
explanatory text.
Fig. 7<br />
The lower cabinet holds three shelf magazines<br />
with printed board assemblies<br />
— individual external abbreviated dialling.<br />
The function is programmed by<br />
the operator and can be used by extensions<br />
with push-button sets<br />
— call waiting function for in<strong>com</strong>ing external<br />
calls<br />
— direct switching to a loudspeaking<br />
telephone.<br />
Classification of the extensions<br />
Each extension can be allocated individually<br />
to one of 12 facility categories<br />
and also one or more of four categories<br />
for the control of long-distance calls.<br />
There is also the possibility of allocating<br />
the extensions other facility categories<br />
which automatically <strong>com</strong>e into operation<br />
when the PABX is set up for night<br />
service. Each facility category <strong>com</strong>prises<br />
one or more of the following basic<br />
facilities:<br />
— open for all automatic outgoing trunk<br />
line traffic<br />
— open for operator-assisted outgoing<br />
and in<strong>com</strong>ing trunk line traffic<br />
— open for transferred trunk line traffic<br />
— barred for cutting in<br />
— open for the call-waiting function initiated<br />
by the operator<br />
— vacant<br />
The relationship between extensions<br />
and facility categories is flexible and<br />
programmed into the data store from<br />
the operator's set or a typewriter terminal.<br />
Of the four categories used for the<br />
control of long-distance calls, one indicates<br />
that calls are permitted within the<br />
local area and the other three are used<br />
for opening up certain trunk code<br />
areas/subscriber numbers. In this way<br />
up to 32 directions, which can be defined<br />
with a maximum of 8 digits, can be<br />
opened. As can be seen from the above,<br />
these 32 directions can be divided into a<br />
maximum of three groups.<br />
Call pick-up<br />
This function means that a call to a<br />
free extension can be answered from<br />
another extension. This is arranged by<br />
dialling a special code, which includes<br />
the number of the called free extension.<br />
External abbreviated dialling<br />
ASB 100 offers the possibility of both individual<br />
and <strong>com</strong>mon external abbreviated<br />
dialling. This makes it possible for<br />
the extensions to reach certain previously<br />
selected subscribers in the national<br />
or international network by dialling<br />
two or three-digit numbers. This<br />
facility can also be used by extensions<br />
that are barred for national and international<br />
calls. The programming of the<br />
subscriber numbers that are to be<br />
reached when an abbreviated number is<br />
dialled is carried out from the operator's<br />
set or a typewriter terminal.<br />
The abbreviated numbers can consist of<br />
subscriber numbers or a part of these. In<br />
the latter case the additional digits required<br />
to <strong>com</strong>plete the whole subscriber<br />
number can be dialled from the extension.<br />
This is an advantage if, for example,<br />
it is desired to open a whole or a part<br />
of a trunk code area to all extensions, or<br />
in the case of traffic to PABXs that are<br />
equipped for direct inward dialling.<br />
ASB 100 permits the storage of up to 35<br />
<strong>com</strong>mon abbreviated numbers in the<br />
smaller version and up to 90 in the<br />
larger. These numbers can consist of a<br />
maximum of 20 digits, where access<br />
codes and intermediate tones are also<br />
counted as digits. Six individual abbreviated<br />
numbers can be allocated to each<br />
of a maximum of 10 extensions in the<br />
smaller version and 20 in the larger. The<br />
individual numbers can consist of a<br />
maximum of 12 digits each, where the<br />
digits are counted in the same way as for<br />
the <strong>com</strong>mon abbreviated numbers<br />
above.<br />
Call waiting function<br />
Thisfunction means that when handling<br />
an in<strong>com</strong>ing call to an extension that is<br />
already busy, the operator can send a<br />
short tone to indicate that there is a call<br />
waiting. The extension can then take the<br />
new call either by finishing off or parking<br />
the existing call.<br />
Optional facilities<br />
The following functions are considered<br />
as optional facilities because they require<br />
extra equipment. However, the required<br />
programs are included in the<br />
program store boards in the basic<br />
equipment for the exchange.<br />
— operator-controlled call metering<br />
— through-connection of trunk lines<br />
— individual call metering<br />
— paging by means of visual or radio<br />
signals<br />
— junction lines<br />
— busy indication panel.
17<br />
Fig. 8<br />
Printed board assembly for a 12x28 switching<br />
network matrix<br />
Operator's set and operator<br />
functions<br />
The operator is responsible for a large<br />
part of the service offered to the callers.<br />
During the design work every effort has<br />
therefore been made to provide a functionally<br />
correct design for the operator's<br />
console. The aim has been to achieve<br />
the best possible relation between man<br />
and machine, fig. 3.<br />
This has led to a minimisation of the<br />
number of function buttons and the use<br />
of explanatory symbols instead of text.<br />
The training of new operators is simplified<br />
because the set is equipped with an<br />
information panel, in which it is possible<br />
to trace the setting up of a call through<br />
the exchange.<br />
In addition to the facilities ASB 100 offers<br />
for the normal handling of calls,<br />
functions can also be included that enable<br />
the operator to take an active part in<br />
the administration of the exchange if<br />
desired. These <strong>com</strong>prise such functions<br />
as changing and checking the extension<br />
categories and directory numbers,<br />
programming of external abbreviated<br />
numbers and call forwarding etc.<br />
ASB 100 is designed for use with one<br />
operator's console. This is usually connected<br />
by means of a plug to a wallmounted<br />
jack, but can also, for example<br />
during the testing stage, be connected<br />
to the exchange cabinet. The console<br />
can be placed up to 50 m (15 ohms)<br />
from the exchange equipment without<br />
any extra equipment being required.<br />
Mechanical construction<br />
Printed board assemblies, shelves<br />
and cabinets<br />
All <strong>com</strong>ponents in ASB 100 are mounted<br />
on printed boards. These have single or<br />
double-sided foil with the exception of<br />
the processor boards, which are manufactured<br />
using four-layer technique.<br />
The printed board assemblies are<br />
mounted in 19" shelves. Three such<br />
shelves form a triple magazine and constitute<br />
one unit with a <strong>com</strong>mon rear<br />
plane, where all wiring between the assemblies<br />
is carried out. The magazines<br />
are mounted in cabinets of two different<br />
sizes.<br />
The racks contain no wiring. All wiring<br />
within the magazines is done on the<br />
<strong>com</strong>mon rear planes of the magazines,<br />
and the wiring between magazines and<br />
to external units is done with the aid of<br />
plug-in, standardized factory-made cables.<br />
Power supply<br />
ASB 100 is normally equipped with a<br />
built-in power unit, which is designed<br />
for feeding from the mains and for providing<br />
the power needed to operate the<br />
exchange. This unit, which is placed at<br />
the bottom of the exchange cabinet,<br />
converts the a.c. mains voltage to a 48 V<br />
d.c. voltage.<br />
Installation and testing<br />
Because of its <strong>com</strong>pact structure ASB<br />
100 requires <strong>com</strong>paratively little space.<br />
The floor area required is approximately<br />
2 m 2 , which also includes the necessary<br />
free space around the exchange.<br />
The installation of the exchange itself<br />
can be said to <strong>com</strong>prise mainly three<br />
activities:<br />
— mounting theexchangeand connecting<br />
external units and power<br />
— input of the system data<br />
— installation testing.<br />
During the design of the system and the<br />
establishment of the system handling<br />
routines the objective has been to reduce<br />
the installation work, and thus also<br />
the installation time, to a minimum. This<br />
has resulted in, for example, the following<br />
features:<br />
— the exchange can be delivered to the<br />
customer <strong>com</strong>plete and tested<br />
— all external connections are carried<br />
out with standardized cables equipped<br />
with plugs<br />
— system data can be programmed<br />
quickly by means of special <strong>com</strong>mands,<br />
which makes it possible to<br />
program in "standard data" for all extensions<br />
by means of a single <strong>com</strong>mand.<br />
Hence the installer does not<br />
need to program data individually for<br />
each extension, only modify data for<br />
the extensions where this is necessary<br />
— system data can be programmed up<br />
to four days before the PABX is put<br />
into operation<br />
— advanced test and fault localization<br />
programs are available if required.
18<br />
Fig. 9<br />
Typewriter terminal for <strong>com</strong>munication with the<br />
exchange<br />
Operation and maintenance<br />
The principle for the operation and<br />
maintenance of ASB 100 can be summarized<br />
as follows:<br />
— the operation of the exchange is continuously<br />
supervised by a built-in<br />
supervisory system<br />
— if disturbances occur, measures to<br />
limit the effect of these are carried out<br />
automatically<br />
— all preventive maintenance and all<br />
routine testing during the operation<br />
of the exchange is avoided<br />
— it is possible to carry out fault localization<br />
down to the printed board assembly<br />
level with the aid of simple<br />
tools.<br />
Operational supervision<br />
In the case of an exchange of this size<br />
the program volume must be kept as<br />
small as possible for reasons of<br />
economy and reliability.<br />
Since the number of <strong>com</strong>ponents is<br />
small and the reliability is high, ASB 100<br />
requires only a few supervisory functions,<br />
primarily for the supervision of the<br />
control system.<br />
The system contains the following<br />
supervisory functions that can give<br />
alarms:<br />
— a hardware circuit that supervises the<br />
progress of the program handling<br />
— a disturbance ratio supervision function<br />
that counts the number of connections<br />
and disturbances<br />
— supervision of the power supply unit<br />
when the exchange is fed from both<br />
the mains and batteries.<br />
Alarms from the supervisory functions<br />
of the exchange are obtained both in the<br />
exchange and on a lamp in the<br />
operator's console as follows:<br />
— time supervision alarm gives steady<br />
light<br />
— disturbance ratio alarm gives slowly<br />
flashing light<br />
— voltage alarm gives rapidly flashing<br />
light.<br />
It is also possible to have these alarms<br />
indicated on a separate panel. The exchange<br />
itself also contains an observation<br />
alarm function that indicates if any<br />
units are blocked or any printed board<br />
assemblies have been removed.<br />
The function "disturbance marking of<br />
devices and data areas" has been introduced<br />
in order to limit the number of<br />
traffic disturbances caused by technical<br />
faults as far as possible.<br />
This means that after devices or data<br />
areas have caused a disturbance marking<br />
they will not be selected until all devices<br />
or areas without faults are engaged.<br />
If a connection attempt with a<br />
marked device or area is then successful,<br />
the disturbance marking will be<br />
cancelled.<br />
Disturbance marking can be initiated<br />
for, for example, the devices and store<br />
areas included in a disturbed connection.<br />
Disturbance marking is also<br />
obtained for breaks or shortcircuits on<br />
external lines in those cases where<br />
supervision is possible. This supervision<br />
is normally in the form of supervision of<br />
the current feeding and then only when<br />
it is a question of closed circuit current.<br />
Aids<br />
ASB 100 is designed to permit a certain<br />
amount of <strong>com</strong>munication with the<br />
system from the units that are always
Technical data<br />
Capacity<br />
Number of extensions 40 100<br />
Trunk lines incl. junction<br />
lines 12 24<br />
Local junctors 5 10<br />
Tone senders 3 6<br />
Operators 1 1<br />
Dimensioned for 0.17 erlangs with a congestion<br />
of 0.01 and 20-40% internal traffic.<br />
Cabinet Height Width Depth<br />
mm mm mm<br />
40 extensions 1068 600 300<br />
100 extensions 1800 600 300<br />
Telephone sets with dial for 10 or 16 Hz and<br />
the pulse ratio 30/70-50/<br />
50;<br />
with push-button set for<br />
tone frequency key sending<br />
in accordance with CCITT<br />
Current feeding 2\400 ohms<br />
Loop resistance max. 1800 ohms for extension<br />
lines, including the<br />
telephone set, max. 1000<br />
ohms for exchange lines<br />
Leakage resistance min. 40 kohms<br />
Attenuation 0.8 dB on exter- 1<br />
nal circuits<br />
7 dB on internal<br />
circuits<br />
at8Q0Hz<br />
Crosstalk attenuation min. 80 dB at 1100 Hz<br />
Numbering two or three-digit extension<br />
numbers<br />
Power feeding 110/127/220/230/240 V a.c,<br />
50/60 Hz or 42- 54 V da,<br />
max. power consumption<br />
250 W<br />
Environment +5° to +40°C ambient temperature<br />
20-80 % relative humidity<br />
connected to the exchange, i.e. telephone<br />
sets and the operator's console<br />
Thus, for example, data concerning test<br />
connections can be programmed from a<br />
push-button telephone and most of the<br />
administrative data for the exchange,<br />
such as classes of service and<br />
abbreviated numbers, can be programmed<br />
from the operator's console.<br />
It is thus always possible to administer<br />
the exchange and carry out simple fault<br />
localization without having to introduce<br />
extra equipment. However, it is possible<br />
to connect an I/O device of standard<br />
type to the exchange when large<br />
quantities of data have to be fed in, for<br />
example when the exchange is put into<br />
operation or when advanced test and<br />
fault localization programs are run. For<br />
this purpose the exchange is equipped<br />
with a terminal outlet with a standardized<br />
interface in accordance with<br />
CCITT V24. A portable typewriter terminal<br />
is normally connected, but a display<br />
terminal can be used instead. Remote<br />
<strong>com</strong>munication via modems is also possible.<br />
Normally the I/O function is not permanently<br />
connected, but is introduced in<br />
the system when required by inserting<br />
the necessary memory and interface<br />
boards.<br />
The I/O device can be used for:<br />
— programming of system data<br />
— initiation of test programs<br />
— printout of the results of test programs<br />
— printout of devices with disturbance<br />
marking<br />
19<br />
— printout of busy, blocked or test<br />
marked devices<br />
- printout of traffic recording data.<br />
Fault localization<br />
Fault localization in ASB 100 can be carried<br />
out either by means of test connections<br />
or program-controlled tests.<br />
Test connections are programmed from<br />
a normal push-button telephone or from<br />
the I/O device.<br />
Program controlled tests are carried out<br />
from the I/O device with the aid of special<br />
test programs. The boards with<br />
these can either be permanantly connected<br />
in the exchange or plugged in<br />
when required. They permit quick<br />
localization of faults down to the printed<br />
board assembly level.<br />
The tests can be carried out without disturbing<br />
the normal operation of the exchange.<br />
Command language<br />
Aspecial <strong>com</strong>mand language is used for<br />
<strong>com</strong>munication with ASB 100 from the<br />
typewriter terminal. A <strong>com</strong>mand consists<br />
of a <strong>com</strong>mand word and in certain<br />
cases a parameter part where the<br />
parameters are separated by colons.<br />
The <strong>com</strong>mand word consists of a<br />
mnemonic <strong>com</strong>bination of five letters,<br />
where the two first letters define the<br />
function, the next two define the subgroup<br />
within this function and the last<br />
letter defines the order that is to be carried<br />
out.
Field Trial with Common Channel<br />
Signalling<br />
Henning Andersen and Villy K. Pedersen<br />
The Danish telephone <strong>com</strong>pany Jydsk Telefon A/S, JTAS, and LM Ericsson have in<br />
close collaboration carried out a field trial with <strong>com</strong>mon channel signalling, CCS, in<br />
Denmark. The trial took place in the Mundelstrup telephone exchange, which belongs<br />
to Arhus local exchange area. The primary objective was to investigate how<br />
well the existing local exchange system could be adapted to <strong>com</strong>mon channel<br />
signalling, in accordance with CCITT system No. 6, but restricted to the register<br />
signals. The existing system originally consisted of the LM Ericsson crossbar<br />
system ARF 100, which was modernised to ARE 11 through the introduction of ANA<br />
30\<br />
The trial provided excellent opportunities for assessing if and when it would be<br />
suitable to introduce <strong>com</strong>mon channel signalling in the network of JTAS. It can then<br />
be a question of either system No. 6 or its planned successor, system No. 7, for<br />
which CCITT is now preparing specifications.<br />
The article gives a short description of signalling system No. 6. The structure and<br />
function of the field trial model are then described, after which the results of the trial<br />
are evaluated. Finally there is some mention of the future plans for CCS.<br />
Around 1970 plans were begun to introduce<br />
PCM systems and, with the aid of<br />
ANA 30, stored program control in the<br />
Arhus local exchange area. In connection<br />
with this there was a desire to investigate<br />
what the technical and financial<br />
consequences would be of conforming<br />
to the latest developments in<br />
the signalling field. JTAS therefore decided<br />
that a field trial should be carried<br />
out.<br />
The work was undertaken by a working<br />
group, with members from JTAS and LM<br />
Ericsson. Both parties contributed to<br />
the good results of the trial, which lasted<br />
from September 1974 to November<br />
1976.<br />
UDC621 395 631<br />
An article in an earlier issue of Ericsson<br />
Review described how field trials had<br />
been carried out with signalling system<br />
No. 6for international telephone circuits<br />
connected up via an international transit<br />
exchange AKE 13 in Australia 2 . The final<br />
CCITT specifications were prepared taking<br />
into consideration the experience<br />
gained from these trials.<br />
However, <strong>com</strong>mon channel signalling is<br />
not reserved for international circuits<br />
only, but can be used at all levels in the<br />
telephone network. Thus variants of<br />
system No. 6 have be<strong>com</strong>e widespread<br />
in the national networks in the USA and<br />
Japan.<br />
Characteristics of signalling<br />
system No. 6<br />
Signalling system No. 6 has been developed<br />
entirely within CCITT, and is described<br />
in the Orange Book, Vol. VI. 2 3 . A<br />
summary of the contents is given below.<br />
The system can be used on all types of<br />
international and national circuits, including<br />
multi-exchange local networks.<br />
However, in national applications certain<br />
additional signals are required. The<br />
system is primarily intended for stored<br />
program controlled exchanges. It is a<br />
link-by-link system, which means that<br />
the signals are regenerated in each<br />
fig. 1<br />
Channel-associated signalling<br />
FUR Outgoing junction line relay set with line signalling<br />
FIR In<strong>com</strong>ing |unctlon line relay set with line signalling<br />
" ^ Register signalling
21<br />
HENNING ANDERSEN<br />
VILLYK. PEDERSEN<br />
Jydsk Teleton A/S, Arhus. Denmark<br />
Fig. 3<br />
The four types of bit pairs and the corresponding<br />
phase shift angle of the carrier<br />
transit point before being transferred<br />
from one link to another.<br />
In older signalling systems there is always<br />
an unambiguous physical connection<br />
between each speech connection<br />
and the signals associated with it. Consequently<br />
this signalling method is called<br />
channel-associated signalling, fig. 1.<br />
The signals are usually transmitted in<br />
the speech channel or in a band that belongs<br />
to the channel but lies outside the<br />
transmitted speech band. In signalling<br />
system No. 6, on the other hand, a separate<br />
signalling channel is used, which is<br />
<strong>com</strong>mon for a large number of speech<br />
channels, and which transmits the signals<br />
required for all these channels. This<br />
method is therefore called <strong>com</strong>mon<br />
channel signalling, fig. 2.<br />
Thus a signal that is transmitted in the<br />
<strong>com</strong>mon signalling channel is not<br />
physically tied to a particular speech<br />
channel, and hence each signal must be<br />
provided with a speech channel label<br />
that indicates the speech channel to<br />
which the signal belongs.<br />
All channel-associated signalling systems<br />
require that the in-band signals are<br />
transmitted without errors in both directions<br />
if it is to be possible to establish a<br />
connection. This provides an automatic<br />
check that there are no faults in the<br />
speech path before the call is set up.<br />
Since the signals in system No. 6 are<br />
transmitted over a separate channel it is<br />
possible that everything functions normally<br />
except the speech transmission.<br />
Consequently with this system the<br />
speech paths are checked with a tone of<br />
2000 ±20 Hz before the call is set up.<br />
The system is designed primarily for<br />
analogue transmission systems, since it<br />
was assumed during the development of<br />
the system that this type of transmission<br />
would be predominant on international<br />
lines during the estimated life of the<br />
system. However, a modified version of<br />
the system can be used for digital<br />
transmission systems (PCM).<br />
Analogue version<br />
In the analogue version a data link is<br />
used that consists of a normal 4-wire<br />
circuit for telephony. The transmission<br />
speed is 2400 bits/second. Both ends of<br />
the data link are connected to so-called<br />
four-phase modems, with the binary<br />
data signals grouped in bit pairs (dibits)<br />
(00, 01, 11 and 10), where each pair corresponds<br />
to one of the four phase positions<br />
of the signal carrier. The pair that is<br />
the next to be transmitted initiates a shift<br />
to the phase angle required for sending<br />
the information, fig. 3.<br />
There is a constant bit stream in both<br />
directions over the data link. It is filled<br />
with non-informative signals, so-called<br />
Fig. 2<br />
Common channel signalling in accordance with<br />
CCITT system No. 6<br />
© The <strong>com</strong>mon signalling channel is a data link<br />
consisting of a normal 4-wire circuit<br />
@ Four-phase modem for the transmission of bit<br />
pairs (dibits)
Fig. 4<br />
Signal flow<br />
(T)<br />
Includes 11 bits that state which signals were<br />
received correct and faulty respectively<br />
Fig. 5<br />
Example of a star-shaped signalling network<br />
with two signal transfer points STP1 and STP2<br />
^—• Alternative speech routes between A and B<br />
~— Speech paths for STP1<br />
^ - Speech paths for STP2<br />
O Exchange<br />
Signal transfer point STP<br />
A Local exchange A<br />
B Local exchange B<br />
Ti Local transit exchange 1<br />
T2 Local transit exchange 2<br />
synchronization units (SYU), when there<br />
is no need of real signal information.<br />
The bit stream is divided into signal<br />
units (SU) consisting of 28 bits, of which<br />
the last eight are check bits, fig. 4. With<br />
the aid of these the receiving signal<br />
terminal decides whether the received<br />
signal unit is correct or faulty.<br />
Twelve signal units form a block, with<br />
the twelfth unit consisting of an acknowledgement<br />
unit (ACU). The information<br />
from the check bits is transferred to<br />
ACU, where a decision is made as to<br />
which signal elements, if any, are to be<br />
returned because of faulty transmission.<br />
The previously mentioned synchronization<br />
unit (SYU) contains a determined<br />
bit pattern. Apart from its use as a filler<br />
to make up a continuous bit stream, SYU<br />
is used the first time the data link is<br />
started up. Only synchronization and<br />
acknowledgement signals are then sent<br />
until the signal terminals at both ends<br />
are synchronized at bit, signalling unit<br />
and block level.<br />
Digital version<br />
In the digital (PCM) version of signalling<br />
system No. 6 the following bit rates are<br />
used:<br />
- bit rates of 4 and 56 kbit/s for 30/32-<br />
channel PCM. This is the European<br />
standard and the signal bit stream is<br />
transmitted in a special time slot (No.<br />
16)<br />
- a bit rate of 4 kbit/s for 24-channel<br />
PCM systems, which are widely used<br />
in the USA and Japan.<br />
Some facts concerning<br />
the field trial<br />
The following basic facts are given in<br />
order to make it easier to understand<br />
how the field trial model in its entirety<br />
functions.<br />
A SPC exchange of type ARE 11 always<br />
contains a control system ANA 30. When<br />
an ARF 10 exchange is modernised by<br />
the inclusion of ANA 30 it also be<strong>com</strong>es<br />
a SPC exchange, and its type designation<br />
is changed to ARE 11.<br />
The normal version of ARE 11 with ANA<br />
30 and the associated software have<br />
been described in two articles in Ericsson<br />
Review 4-5 .<br />
Special processor functions are added<br />
for <strong>com</strong>mon channel signalling<br />
The normal version of ARE 11 contains<br />
two types of processors, namely traffic<br />
control processors TCP and operation<br />
and maintenance processors OMP.<br />
Signalling system No. 6 requires the<br />
addition of a <strong>com</strong>mon channel signalling<br />
processor CCP in the terminal exchange<br />
and a signal transfer point processor<br />
SPP for STP functions. All processor<br />
types consist of the same hardware.<br />
Thus if there is unused capacity in<br />
a TCP it can be provided with the required<br />
software and also used as CCP.<br />
Star-shaped signalling network<br />
In spite of the mesh-shape of the speech<br />
network in the Arhus area, the field trials<br />
were optimized for a star-shaped signalling<br />
network with two signal transfer<br />
points, STP1 and STP2, in accordance<br />
with the example in fig. 5. Each STP is<br />
normally situated in or near a telephone<br />
exchange, which does not need to be<br />
included in the speech connection but<br />
which transfers the CCS signals.<br />
Each exchange must then have at least<br />
one signalling channel to each STP, and<br />
the signalling traffic is usually divided<br />
equally between these channels (load<br />
sharing). This saves time since the queuing<br />
time is reduced, and also provides<br />
greater reliability because of the duplication.<br />
If a fault occurs in one channel,<br />
the signalling in question is transferred<br />
to the other channel.<br />
The maximum number of speech<br />
channels<br />
There is an upper limit to how many<br />
speech channels a signalling channel<br />
can serve, since it can only transmit a<br />
limited number of signals per unit of<br />
time. This limit is dependent on, for<br />
example, the average seizure time of the<br />
speech channel, and thus it varies in different<br />
applications. In the Mundelstrup<br />
trial, where the signalling channel could<br />
only transmit register signals, a signalling<br />
channel served approximately 1960<br />
speech circuits, which would be reduced<br />
to 980 if the line signals were also<br />
included.<br />
Different signalling possibilities<br />
The analogue version of the signalling<br />
svstem was used for the field trial, but
23<br />
signalling was to be carried out over the<br />
speech wires in accordance with the existing<br />
principles. The speech transmission<br />
paths were thereby automatically<br />
checked, and hence the continuity<br />
check of the speech paths re<strong>com</strong>mended<br />
by CCITT could be omitted in<br />
the field trial.<br />
Fig. 6<br />
Schematic picture of the Mundelstrup field trial<br />
equipment with a signal transfer point STP and<br />
signalling conditions that are typical for Arhus<br />
local exchange area<br />
Speech circuit A - B - C<br />
Signalling circuit A- B and the designation forcertain<br />
signals sent via it<br />
Signalling circuit B — C and the designation tor certain<br />
signals sent via it<br />
Fig. 7<br />
Block diagram for the field trial equipment in<br />
Mundelstrup with <strong>com</strong>mon channel signalling<br />
CCP<br />
SPP<br />
GV-KME<br />
DC-I<br />
Common channel signalling processor<br />
Signal transfer processor<br />
Code receiver<br />
Interlace equipment<br />
Equipment that has been added tor the<br />
— field trial<br />
Equipment that has been changed for the<br />
field trial<br />
the software was also prepared for the<br />
digital version with a transmission<br />
speed of 4 kbit/s. Facilities were also<br />
provided for conversion between <strong>com</strong>mon<br />
channel and d.c. code signalling,<br />
as well as for connecting via two transit<br />
exchanges.<br />
As has been mentioned above, for this<br />
project it was decided that the line<br />
Traffic cases<br />
The field trial equipment consisted of a<br />
signalling link, with both ends connected<br />
to a processor in ANA 30 via a<br />
signal terminal. Another of the exchange<br />
processors could be connected<br />
in to and disconnected from the signalling<br />
link, and was thus able to function<br />
as a signal transfer point STP when required.<br />
In this way it was possible to set<br />
up connectionsthat represented signalling<br />
circuits within the whole of the Arhus<br />
local exchange area, including<br />
connection to transit exchange AKE 13.<br />
Fig. 6 shows how a local transit circuit<br />
from A to C is set up with signalling via<br />
STP.
Fig. 8<br />
Block diagram for the signal terminal<br />
TCP<br />
CCP<br />
Traffic control processor<br />
Common channel signalling processor<br />
Description of the special<br />
equipment for CCS<br />
Fig. 7, which contains a block diagram<br />
of the whole of the Mundelstrup exchange,<br />
indicates the equipment that<br />
was added for the field trial. Small<br />
changes in ANA 30 were also carried<br />
out.<br />
Signal terminal<br />
A signal terminal is shown in fig. 11. It<br />
serves as an interface stage between a<br />
processor and a modem for 2400 bit/s. It<br />
is used both in the local exchange and<br />
the signal transfer point, STP, and contains,<br />
among other things, transmitting<br />
and receiving bufferfunctionsfortaking<br />
up the difference in speed between processor<br />
and modem, fig. 8.<br />
Common channel signalling processor<br />
CCP<br />
CCP generates CCS signals under the<br />
control of a traffic control processor<br />
TCP (or the operation and maintenance<br />
processor OMP). These signals are<br />
transmitted to a signal terminal in a predetermined<br />
order of priority. CCP also<br />
receives and analyzes signals from the<br />
signal terminal and distributes them to<br />
the TCP or the OMP concerned, fig. 9.<br />
Communication between them takes<br />
place via the translation store TRS.<br />
CCP also generates synchronization<br />
and acknowledgement signals, and retransmits<br />
the signals that are found to<br />
be faulty.<br />
15 new programs have been developed<br />
for the above-mentioned purposes, and<br />
a number of data pages have also been<br />
allocated to them.<br />
Because of the importance of its functions<br />
CCP has been duplicated. In implementing<br />
this, the principle has been<br />
applied that no information shall be lost<br />
when changing over from theworkingto<br />
the standby processor.<br />
Additions to the existing ANA 30<br />
system<br />
FUR and FIR labels have been introduced<br />
in the existing ANA 30 equipment<br />
in the Mundelstrup exchange. It should<br />
be mentioned, however, that the latest<br />
version of ANA30includesthis possibility<br />
as a standard feature.<br />
The FUR label identifies the selected device<br />
in a group of 20 outputs in the first<br />
group selector (IGV) stage. Its code receiver<br />
GV-KME stores this label, which<br />
is then read out by TCP (fig. 7).<br />
The label of a FIR call is given by the<br />
register finder inlet (one of 64). It is<br />
transmitted by the interface equipment<br />
DCI-one per register finder marker<br />
RSM-to the identifier IDS, from which<br />
TCO reads the RSM number and FIR<br />
label.<br />
Fig. 9<br />
Communication between CCP and TCP is handled<br />
by the translation store TRS<br />
CCP<br />
TCP<br />
TRS<br />
Common channel signalling processor<br />
Traffic control processor<br />
Translation store
25<br />
Fig. 10<br />
Simplified block diagram for the setting up of i<br />
transit connection with signalling via a signal<br />
transfer point, STP. The signal terminals and<br />
4-phase modems are not shown<br />
^ Call with conventional line signalling<br />
»- Initial address message, IAM<br />
Subsequent address messages, SAM<br />
», Free B-subscriber<br />
Signal transfer processor SPP<br />
SPP works in accordance with the same<br />
principles as CCP. Thus the signals go<br />
from SPP in a certain order of priority to<br />
a signal terminal. When receiving, SPP<br />
reads off the in<strong>com</strong>ing signals in the<br />
signal terminal. These signals are<br />
analysed. The ones that are to be sent on<br />
gettheirlinkand "band" numbers translated<br />
in a translation table. By band<br />
number is meant the seven most<br />
significant bits in the speech channel<br />
label. It has thereby been possible to reduce<br />
the size of the table.<br />
SPP is duplicated in the same way as<br />
CPP.<br />
Carrying out the field trial<br />
The following equipment was used for<br />
the field trial:<br />
— Control system ANA 30 with two processors<br />
TCP supplemented with CCP<br />
and STP functions, an OMP, a SCS<br />
and a TRS<br />
— Interworking equipment between the<br />
switching equipment and the control<br />
system, model Arhus<br />
— Subscriber (SL) stage, 1000 multiple<br />
positions<br />
— Group selector (GV) stage, 80 inlets<br />
— SR, LKR, FUR and FIR.<br />
With this limited range of equipment it<br />
was not possible to generate sufficient<br />
traffic for test connections. Simulated<br />
traffic, which was generated by a special<br />
program in OMP, was therefore used to<br />
increase the signal traffic by 0.2 — 1<br />
erlang.<br />
The real traffic was superposed on the<br />
simulated traffic and was measured by a<br />
special program in CCP and SPP respectively.<br />
The program was handled in<br />
free time slots. The measurements were<br />
used to determine the transfer times between<br />
buffers for the signals passed in<br />
the system. From the results it was possible<br />
to evaluate the system signalling<br />
times and to <strong>com</strong>pare these with the<br />
CCITT specification.<br />
The field trial covered all traffic cases<br />
that represent normal signalling conditions<br />
in the Arhus local network, including<br />
transit connection and also connections<br />
to AKE 13 in the Slet exchange and<br />
STP.<br />
However, it was not possible to carry out<br />
certain special tests because of the limited<br />
amount of equipment. The most<br />
important of the tests that could not be<br />
carried out was the changeover from<br />
STP1 to STP2.
26<br />
Simplified description of the<br />
setting up of a connection<br />
A brief account is given here of how a<br />
transit connection is set up with signalling<br />
via a separate signal transfer point<br />
STP, figs. 6 and 10. The call attempt<br />
starts with a signal transfer unit STU-L<br />
being connected in and receiving digits.<br />
After three digits a FUR is selected under<br />
the control of TCP. The corresponding<br />
FIR in exchange B is called by means<br />
of conventional line signalling.<br />
The TCP in exchange A reads the FUR<br />
label. It transfers the first three digits<br />
and the speech channel label to CCP,<br />
which then generates the initial address<br />
message, IAM. This signal is sent via the<br />
signalling channel to STP, where it is<br />
analyzed and the label is translated. The<br />
signal is then sent to exchange B, where<br />
it is analyzed by TCP on the initiative of<br />
the called FIR, which has been connected<br />
to a signal translation unit STU-I.<br />
If the call turns out to be to exchange C,<br />
a FUR is selected, which calls the corresponding<br />
FIR in exchange C. In the<br />
normal way the TCP in exchange B<br />
transmits a signal to CCP, giving the<br />
speech channel label of the selected<br />
FUR. CCP then sends IAM to STP, where<br />
it is analyzed and the label is translated<br />
before being sent on to exchange C.<br />
In exchange C TCP decides that the call<br />
in question is a terminating one and<br />
waits for the remaining digits. When<br />
these have been received in exchange<br />
A and transferred from TCP to CCP, the<br />
latter generates a subsequent address<br />
message SAM and sends it to STP.<br />
The procedure is then the same as for<br />
the initial address message. Thus SAM<br />
is transmitted via STP-^B->STP-^C,<br />
with translation of the speech channel<br />
label in STP and B.<br />
When the remaining digits have been<br />
received in exchange C the switching<br />
stage is set up and the line state of the B<br />
subscriber is determined. If the line is<br />
free, TCP sends the appropriate signal<br />
to CCP, which then sends the free signal<br />
and speech channel label for the FIR in<br />
question in the return direction via C-*<br />
STP-^B^STP-^A.<br />
This free signal results in the speech<br />
circuit being through-connected at<br />
these three exchanges.<br />
Result<br />
The field trial has provided valuable experience<br />
of the CCS system and its<br />
adaption to the national network at the<br />
local exchange level. The trial has<br />
shown that control system ANA 30 is<br />
Fig. 11<br />
Signal terminal
Fig. 12<br />
The principle for <strong>com</strong>mon transmission equipment<br />
and Individual equipment tor each type ot<br />
<strong>com</strong>munication with the CCITT signalling system<br />
No. 7<br />
References<br />
1. Meland, F. and Rishoj, E.: Crossbar<br />
Exchanges in Arhus be<strong>com</strong>e SPC<br />
Exchanges. Ericsson Rev. 54<br />
(1977):2, pp. 86-89.<br />
2. Hinwood, J. D. and Clark, D. W.:<br />
Field Trial of CCITT Signalling<br />
System using AKE13. Ericsson Rev.<br />
49 (1972):4, pp. 124-138.<br />
3. CCITT Orange Book, Vol. Vl.2.<br />
4. Morlinger, R. and Viktorsson, O.:<br />
ARE 11 -System Description. Ericsson<br />
Rev. 54 (1977):2, pp. 67-76.<br />
5. Hemre, A. and Hagard, G.: The<br />
Software and Its Handling in ARE<br />
System. Ericsson Rev. 54 (1977):2,<br />
pp. 77-85.<br />
6. Andersson, B. et al.: ARE Systems<br />
in Modern Networks. Ericsson Rev.<br />
54(1977):2, pp. 54-66.<br />
very suitable for adaption to CCS signalling<br />
and for STP functions.<br />
With direct signalling between two exchanges<br />
the analogue version of system<br />
No. 6 gives a signalling time that is of the<br />
same order of magnitude as MFC and<br />
d.c. code signalling. In the case of transit<br />
traffic the link-by-link principle is<br />
used for CCS, whereas the faster endto-end<br />
signalling is used for MFC and<br />
d.c. code signalling. Thus in this case<br />
the signalling time is longer for the CCS<br />
analogue version than the other two<br />
methods. This be<strong>com</strong>es more apparent<br />
when the connection is made via two<br />
transit points with signalling via STP.<br />
However, it is possible to start the setting<br />
up process earlier, whereby the wait<br />
for the ringing signal —the post dialling<br />
delay — is reduced to a satisfactory level.<br />
The field trial has not, however, provided<br />
sufficient basic data for reliable<br />
cost calculations, and thus it has not<br />
been possible to make economic <strong>com</strong>parisons<br />
between a CCS and a MFC<br />
network.<br />
Plans for the future<br />
Signalling system No. 6 is now being introduced<br />
on many international telephone<br />
circuits. The interest in CCS has<br />
grown also in other parts of the tele<strong>com</strong>munications<br />
field, which has meant<br />
that the fundamentals of the system are<br />
having to be reconsidered.<br />
Thus it can no longer be assumed that<br />
CCS must only be suitable for international<br />
circuits, where the cost of the<br />
signalling equipment is not decisive.<br />
Now it must also be suitable for the national<br />
network, where the cost aspect is<br />
of greater importance.<br />
Since PCM is now beginning to be an<br />
economic form of transmission even for<br />
long distances, it is possible to use a 64<br />
kbit/s digital channel for CCS. This<br />
means that the signalling rate can be increased,<br />
and furthermore the analogue<br />
modem will not be required.<br />
Finally the introduction of the digital<br />
group selector is now imminent. As was<br />
made clear in a previous article in Ericsson<br />
Review 6 this can be done with<br />
advantage even in an existing ARE<br />
network. This development will lead to a<br />
changed network structure and also the<br />
introduction of concentrators around<br />
the new exchanges. Moreover measures<br />
will then be taken to prepare for an integration<br />
of different forms of <strong>com</strong>munication,<br />
such as telephony, telex,<br />
data, gentex, and also network management,<br />
maintenance etc.<br />
Consequently CCITT is now in the process<br />
of preparing a new CCITT system,<br />
No. 7. It will contain a message transfer<br />
part that is <strong>com</strong>mon for all forms of<br />
<strong>com</strong>munication, and which will constitute<br />
the actual <strong>com</strong>mon signalling<br />
channel. Individual parts, fig. 12, foreach<br />
<strong>com</strong>munication form will then be connected<br />
to the ends of the <strong>com</strong>mon message<br />
transfer part.<br />
The specifications for this signalling<br />
system are expected to be <strong>com</strong>pleted<br />
around 1980. The main features are<br />
already known, however, and thus it is<br />
possible to plan how the system should<br />
be used in principle. It is even considered<br />
that it will be possible to use the<br />
transmission principles of system No. 7<br />
between concentrators and the parent<br />
exchange.
60 MHz Coaxial Cable System for<br />
10800 Channels<br />
Per-Alrik Hallberg, Thorwald Lundmark and Luigi Manes<br />
By extending the band transmitted over coaxial cables to 4-60 MHz it is possible<br />
to transmit 10800 channels, in the form of twelve supermastergroups or six television<br />
channels. LM Ericsson in collaboration with the Italian <strong>com</strong>pany FATME,<br />
which is a member of the Ericsson Group, have developed a 60 MHz system for<br />
coaxial cables, ZAX 10800. The equipment is manufactured in the same construction<br />
practice as the 4 MHz and 12 MHZ coaxial cable systems. The article gives a<br />
description of the equipment and also the result of a field trial in Italy.<br />
with six tubes is 32 400 channels and the<br />
capacity of a cable with twelve tubes is<br />
64 800 channels. This is a very considerable<br />
capacity, which it is rarely desirable<br />
to exceed, among other reasons because<br />
of the consequences of a cable<br />
break. In the case of coaxial cable of<br />
small diameter, however, the repeater<br />
distance will be very short which means<br />
more noise than is desirable.<br />
UDC621 315212<br />
Fig. 1<br />
Equipment for sending and receiving in the line<br />
terminal<br />
COM Combiner<br />
FEQ Fixed equalizer<br />
PE Pre-emphasis network<br />
PEQ Pre-equallzer<br />
LBO Line building-out network<br />
PC Pilot <strong>com</strong>biner<br />
PFU Remote power feeding unit<br />
FLO Fault location oscillator<br />
DE De-emphasis network<br />
EEG Echo equalizer<br />
SEP Separator<br />
The growth of the long-distance traffic<br />
creates a demand for greater traffic capacity.<br />
Since the cost of electronic<br />
equipment is only a fraction of the cost<br />
of cables, existing coaxial cables have<br />
naturally been utilized as far as is technically<br />
and practically possible. A limiting<br />
factor, however, is that the transmission<br />
data of the cable may deviate<br />
so much from the calculated data that<br />
it is difficult to obtain sufficiently accurate<br />
attenuation equalization.<br />
Most existing coaxial cables of normal<br />
diameter are suitable for transmission<br />
of 60 MHz and the cost per channel kilometre<br />
is low even in the case of new<br />
cables because of the high transmission<br />
capacity. The balance between cable<br />
cost and repeater cost is better than in<br />
the case of other 4-wire coaxial systems.<br />
The transmission capacity of a cable<br />
The 60 MHz coaxial cable system for<br />
10800 channels, ZAX 10800, consists of<br />
terminal equipment and line repeaters.<br />
The system is in the LM Ericsson tradition<br />
in this field as regards reliability,<br />
maintainability and mechanical construction<br />
practice.<br />
The terminal equipment is described<br />
first, then the different types of line repeaters<br />
and the power feeding equipment,<br />
followed by regulation, equalization<br />
and fault location. The mechanical<br />
construction is described briefly and<br />
finally the results from a trial route are<br />
presented.<br />
Terminal equipment<br />
The function of the terminal equipment<br />
is to adapt the line band from the multiplex<br />
equipment to what is needed for<br />
transmission over the line, see fig. 1.
PER-ALRIK HALLBERG<br />
THORWALD LUNDMARK<br />
Transmission Division<br />
Telefonaktiebolaget LM Ericsson<br />
LUIGI MANES<br />
FATME, Rome<br />
Fig. 2<br />
Line repeater with fixed gain<br />
Fig. 3<br />
The basic design of the pre-amplifier. In a<br />
regulating line repeater a thermistor T is used<br />
and in a non-regulating repeater a resistor R that<br />
corresponds to a certain gain. RN is a regulating<br />
network.<br />
Fig. 4<br />
The basic design of the power amplifier<br />
Send direction<br />
On the send side the necessary regulating<br />
pilots 61160, 22372 and 4287 kHz<br />
are added and the upper part of the<br />
band is pre-emphasized. It may also be<br />
necessary to include stop filters to suppress<br />
disturbances in the line band at<br />
the pilot frequencies, The frequency<br />
<strong>com</strong>parison pilot 4200 kHz can be fed<br />
into the equipment at a level of 0 dBm<br />
or -7 dBm. It is fed in together with the<br />
other pilots.<br />
The fault location frequencies are generated,<br />
with a unique frequency for each<br />
line repeater, and are supervised at the<br />
receiving terminal. The received frequencies<br />
can be loop connected at one<br />
of the terminals so that all supervision<br />
can be carried out from the other terminal.<br />
The attenuation in the send side station<br />
cable can be equalized by up to 3.5 dB<br />
in an active equalizer, which corresponds<br />
to a line length of approximately<br />
30 m at 60 MHz. The equalizer is also<br />
equipped with two similar inputs, so<br />
that measurements can be carried out<br />
with additional measuring frequencies<br />
during traffic. A corresponding facility is<br />
provided at the output in the receive direction.<br />
Receive direction<br />
The main task of the receive side is to<br />
equalize and regulate the received line<br />
band. This is done with the aid of fixed<br />
equalizers, an echo equalizer and regulation<br />
equipment related to the two<br />
extra pilots 22372 and 4287 kHz. Regulation<br />
with the aid of the main pilot<br />
61160 kHz takes place in the terminal<br />
repeater, where de-emphasis to flat (frequency<br />
independent) level also takes<br />
place. The pilots are suppressed by filters<br />
with 50 dB attenuation.<br />
The frequency <strong>com</strong>parison pilot 4200<br />
kHz, which is only transmitted over the<br />
system and thus is not used for regulation<br />
purposes like the other pilots, is extracted<br />
in a flat amplifier and is fed to<br />
the frequency control equipment in the<br />
station. The flat amplifier also <strong>com</strong>pensates<br />
for the basic loss of the passive<br />
stop filters, and feeds the fault location<br />
frequencies both to the loop connection<br />
and to a test point on the front of<br />
the unit, where they can be checked<br />
with the aid of an external instrument.<br />
Line repeaters<br />
The line repeater is available in three<br />
variants: one with fixed gain, one with<br />
pilot regulation and one for use in the<br />
terminal.<br />
All three have the same mechanical design<br />
and each is a <strong>com</strong>pact unit that includes<br />
the equipment for both directions<br />
of transmission.<br />
Line repeater with fixed gain<br />
The simplest version of the line repeater<br />
has fixed gain. The main parts, fig. 2,<br />
for one direction are<br />
— amplifier<br />
— pre-equalizer<br />
— power separation filters<br />
— line building-out network<br />
and <strong>com</strong>mon for both directions are<br />
— zener diodes<br />
— fault location oscillator.<br />
The amplifier part consists of two 2-<br />
stage amplifiers: one pre-amplifier with<br />
low thermal noise and one power amplifier<br />
with fixed gain and very low harmonic<br />
distortion, figs. 3 and 4. Together<br />
they give a gain of 28.5 dB, which can be<br />
varied over the range ±3 dB, by changing<br />
a resistor in the feedback network.<br />
A transformer is placed between the two<br />
amplifiers in order to provide phase inversion<br />
in each line repeater. In this way<br />
a more favourable addition of the noise<br />
contributions from the individual repeaters<br />
is obtained 6 .<br />
Fig. 5<br />
The principle tor power feeding the line repeaters.<br />
31 -34 are the different connection points. Every<br />
other line repeater is changed over so that the<br />
feeding direction is always changed. This<br />
balances the power feeding relative to earth,<br />
which also leads to a reduction of the hum<br />
modulation.
8<br />
30<br />
Fig. 7<br />
Line repeater with pilot regulation<br />
Both amplifiers are constructed in the<br />
hybrid technique, and in each of them<br />
thick film technique is used for the active<br />
parts and most of the feedback network.<br />
This gives a short feedback loop<br />
and a small phase shift.<br />
A conventional pre-equalizer in the preamplifier<br />
shapes the gain curve at low<br />
frequencies and power separation filters<br />
at the input and output separate and<br />
<strong>com</strong>bine the HF signals and the power<br />
feeding. A line building-out network<br />
provides simulated cable attenuation of<br />
up to 22 dB, i.e. almost a whole repeater<br />
section. The line building-out network<br />
can be placed in any line repeater.<br />
Parallel feeding is used for the power<br />
feeding of the line repeaters in such a<br />
way that one zener diode feeds both<br />
transmission directions, but with a separate<br />
diode for the pre-amplifier and<br />
the power amplifier respectively, fig. 6.<br />
This feeding method requires double<br />
the current but only half the voltage of<br />
series feeding, and hence almost twice<br />
the number of line repeaters can be fed<br />
with this method. This is particularly desirable<br />
in a 60 MHz system since the<br />
distance between the line repeaters is<br />
short.<br />
The line repeaters are well protected<br />
against external electrical disturbances<br />
taken up by the cable, such as lightning<br />
pulses. Gas discharge tubes with a striking<br />
voltage of 1400 V are provided at the<br />
input and output of the repeaters, between<br />
the inner conductor and earth.<br />
The limit frequencies for the power separation<br />
filters are chosen so that as<br />
little as possible of the energy in the<br />
lightning pulse gets into the amplifier<br />
part. The input and output of the amplifier<br />
part are also provided with diode<br />
chains and each transistor is protected<br />
by a base-emitter diode. Thus a whole<br />
series of protective circuits <strong>com</strong>bine to<br />
give the greatest possible operational<br />
reliability.<br />
Line repeater with pilot regulation<br />
The line repeater with pilot regulation<br />
has the same construction as the repeater<br />
with fixed gain, except that a regulating<br />
circuit has been added. This<br />
circuit consists of a pilot receiver equipped<br />
with a digital memory and a thermistor.<br />
The gain is regulated automatically<br />
with the aid of the 61160 kHz pilot<br />
so that the level at the output of the line<br />
repeater is always held at the nominal<br />
value, fig. 7.<br />
The regulation process is as follows:<br />
The pilot signal is extracted at the output<br />
of the power amplifier with the aid<br />
of a crystal filter and is then amplified<br />
and rectified. The pilot voltage thus obtained<br />
is <strong>com</strong>pared with a constant d.c.<br />
voltage in an operational amplifier. The<br />
voltage difference determines the<br />
amount of current through an NTC thermistor<br />
placed in the series branch of the<br />
pre-amplifier feedback network.<br />
If the pilot fails, a digital memory takes<br />
over the control of the thermistor with<br />
the same current that existed immediately<br />
before the loss of the pilot. The<br />
gain conditions that applied will then be<br />
maintained until the pilot returns. The<br />
memory circuit consists of an 8-bit shift<br />
register, with the aid of which the thermistor<br />
current can be reproduced so<br />
that the regulation range is divided into<br />
steps of 2 mB.<br />
The regulation range at 61160 kHz is<br />
±3 dB, of which approximately ±2 dB<br />
is used for variations in the cable at-<br />
Fig. 6<br />
One direction ot the regulating line repeater. The<br />
zener diodes teed the corresponding part in the<br />
other direction<br />
PRA Pre-amplifier<br />
POA Power amplifier<br />
PR Pilot receiver
31<br />
Fig. 9<br />
Regulation range for the main regulating pilot<br />
61160 kHz<br />
tenuation caused by temperature<br />
changes, and ±1 dB for variations in<br />
length when installing the regulating<br />
line repeaters, fig. 9. All gain variation<br />
as a result of the regulation takes place<br />
in the pre-amplifier.<br />
Terminal repeater<br />
The levels between the cable side and<br />
the line terminating equipment are adjusted<br />
with the aid of a terminal repeater,<br />
which on the send side has the same<br />
design as a line repeater with fixed gain<br />
and on the receive side the same design<br />
as a repeater with pilot regulation. The<br />
transmission band is thereby regulated<br />
before equalization. A de-emphasis network<br />
on the output gives the desired flat<br />
level.<br />
An alarm circuit senses the level of the<br />
61160 kHz pilot at the output of the<br />
power amplifier, and if the deviation<br />
after regulation exceeds a preset value,<br />
which can be set to ±0.7, ±1.2 or ±1.7<br />
dB, an alarm is obtained. A separate<br />
outlet is provided, to which a recorder<br />
can be connected for continuously<br />
monitoring the pilot level.<br />
In order to avoid having too high a<br />
voltage in the terminal bay the terminal<br />
repeater is not fed with power from the<br />
remote power feeding system that feeds<br />
the remaining line repeaters. The terminal<br />
repeater is instead fed from a local<br />
21 V d.c. converter.<br />
Power feeding<br />
The equipment can be fed with power<br />
from a 24 V, 36 V, 48 V or 60 V station<br />
battery. It can also be fed from the mains<br />
via a mains rectifier that gives a d.c.<br />
voltage of 41-72 V from 110 V or 220 V<br />
a.c. The mains frequency is allowed to<br />
vary between 45 and 65 Hz. The output<br />
power from the rectifier is 440 W.<br />
Fig. 8<br />
Line repeater with amplifier part, pilot receiver<br />
and power separation filters
32<br />
The terminal equipment for two fully<br />
equipped systems can be mounted in<br />
one bay. The two systems are quite independent<br />
of each other, even as regards<br />
power feeding.<br />
Power feeding of the line repeaters<br />
The line repeaters are power fed from<br />
a remote power feeding unit placed in<br />
the terminal bay. The unit gives a constant<br />
direct current of 290 mA and an<br />
output voltage of 20-1200 V. When<br />
the system is fed from a station battery<br />
and every fourth line repeater is regulating,<br />
up to 47 repeaters can be fed<br />
from the unit, which gives a distance of<br />
147 km between two power-feeding stations,<br />
fig. 12. The given maximum values<br />
for current and voltage are selected with<br />
regard to personal safety when handling<br />
the equipment.<br />
The direct current is fed from the unit<br />
via a separation filter in a power feeding<br />
adapter to the inner conductor of the<br />
coaxial tube (fig. 1). Each line repeater<br />
is then fed in the way shown in figs. 2<br />
and 7. After the last repeater in the<br />
power feeding chain there is a power<br />
looping adapter that takes the current<br />
over to the opposite transmission direction<br />
and back to the remote power<br />
feeding unit.<br />
To ensure reliable operation of the<br />
whole system, including the line repeaters,<br />
the unit is equipped with supervision<br />
and alarm circuits for each of the<br />
following fault conditions:<br />
— current increase<br />
— current decrease<br />
— unbalance of the feeding voltage<br />
— loss of battery voltage.<br />
The different alarm conditions are indicated<br />
by light emitting diodes on the<br />
front of the unit. A <strong>com</strong>mon outlet for<br />
the supervisory circuits can be connected<br />
to the station alarm for indication<br />
of a faulty unit.<br />
For each of the first three supervisory<br />
circuits it is possible to strap so that<br />
when the corresponding fault condition<br />
arises the unit is automatically disconnected<br />
and its output voltage and current<br />
are brought to zero. In addition to<br />
the supervision described above the<br />
unit is provided with an overvoltage protection<br />
that always disconnects the<br />
unit when it operates. This occurs, for<br />
example, in the case of a cable break<br />
because the unit is of the constant current<br />
type and then tries to feed out 290<br />
mA by raising the voltage.<br />
The unit contains two instruments, one<br />
for current and one for voltage measurement.<br />
A potentiometer, accessible<br />
from the front, is used to adjust the outgoing<br />
current to 290 mA. It is easy to<br />
Fig. 10<br />
Adjusting the gain curve
Fig. 12<br />
Power feeding of the line repeaters. A power<br />
looping adapter is placed after the last repeater<br />
in the feeding chain.<br />
Fig. 13<br />
Regulation range for the two pilot regulated<br />
equalizers 22372 kHz and 4287 kHz<br />
determine whether there is any unbalance<br />
because it is possible to measure<br />
the voltage between each inner conductor<br />
and earth. The circuit breaker for<br />
the unit is key controlled, and it is thus<br />
possible to prevent restarts, for example<br />
during maintenance work.<br />
Power feeding of the bay equipment<br />
The units in the line terminating equipment<br />
are <strong>com</strong>bined to form a shelf<br />
stack, those which are active being<br />
power fed from two 12 Vd.c. converters<br />
of 25 W each. One converter is used for<br />
the units in the send direction and the<br />
other for the units in the receive direction.<br />
The 21 V d.c. converter of 30 W which<br />
feeds the terminal repeater is also placed<br />
in the shelf stack. The speaker circuit<br />
shelf is provided with d.c. converters<br />
of its own.<br />
Level regulation<br />
Level variations along the line are caused<br />
by temperature changes in the cable.<br />
The cable attenuation varies approximately<br />
0.2 % per °C. The level variations<br />
are mainly seasonal and are <strong>com</strong>pensated<br />
automatically by regulating line repeaters<br />
along the line and, if necessary,<br />
also by pilot regulated equalizers in the<br />
receive side of the terminal equipment.<br />
The main regulating pilot 61160 kHz is<br />
active in the regulating line amplifiers<br />
and the two extra pilots 22372 kHz and<br />
4287 kHz are active only in their respective<br />
equalizers.<br />
The regulation range varies over the frequency<br />
band, figs. 9 and 13. The range<br />
is ±3 dB at each pilot frequency. Usually<br />
it is sufficient to use single pilot regulation,<br />
i.e. only the main pilot 61160<br />
kHz, for the regulation of the system.<br />
The use of two additional pilots, i.e. 3-<br />
pilot regulation, is necessary only<br />
when the cable is exposed to large temperature<br />
variations or when the route is<br />
very long. For example, when the route<br />
contains an intermediate power feeding<br />
repeater station between the two terminals<br />
the use of 3-pilot regulation should<br />
be considered.<br />
It is sufficient to make every fourth line<br />
repeater along the line regulating as<br />
long as the variation in cable temperature<br />
does not exceed ±10°C. If the variations<br />
are greater than this, every third<br />
or every second repeater must be regulating.<br />
This situation arises when the<br />
cable follows a bridge or a tunnel, since<br />
it must then sometimes be run out in the<br />
open, and is then exposed to rapid and<br />
irregular temperature variations.<br />
Equalization of the line<br />
attenuation<br />
When the system is put into operation<br />
a curve is measured at the receiving terminal<br />
which shows how the level deviates<br />
from the expected value. This deviation<br />
is caused by the differences in the<br />
actual attenuation-frequency characteristic<br />
of the cable in relation to what had<br />
been anticipated. The resultant devia-<br />
Fig. 11<br />
Remote power feeding unit for feeding the line<br />
repeaters
Fig. 14<br />
Location of a faulty line repeater. If one direction<br />
is faulty in line repeater No. 4 only frequencies<br />
t s-f a are obtained at terminal B, whereas all frequencies<br />
f, — t e are obtained at terminal A<br />
tion over the route is eliminated by<br />
means of equalization. The equalization<br />
process is divded into coarse and<br />
fine equalization.<br />
The coarse equalization is carried out<br />
with fixed equalizers, one in the send<br />
direction for pre-equalization of the line<br />
and two in the receive direction for<br />
more accurate post-equalization. Each<br />
such device holds three correction networks.<br />
Theamount of equalization available<br />
in each direction of transmission is<br />
6dB.<br />
The fine equalization is carried out by<br />
means of what is called an echo equalizer,<br />
which is based on the use of a delay<br />
line. The device contains 30 outlets,<br />
each of which has a variation range of<br />
±3 dB. Adjustments are made with a<br />
potentiometer that is accessible at the<br />
front of the unit. A residual deviation<br />
curve can quickly be equalized with this<br />
equalizer. This equalizer can also be set<br />
up when the system is in service by<br />
using external test equipment and sending<br />
additional measuring frequencies<br />
over the system from the other terminal<br />
and measuring them.<br />
In addition to the equalization in the line<br />
terminal an equalization board can, if<br />
necessary, be included in each transmission<br />
direction in one of the non-regulating<br />
line repeaters. This board is designed<br />
as a fixed equalizer and the number<br />
required on a certain route will depend<br />
on how well the attenuation-frequency<br />
characteristic of the cable and<br />
the gain-frequency characteristic agree.<br />
To sum up it can be said that on short<br />
routes it is sufficient to have only fixed<br />
equalizers, or alternatively an echo<br />
equalizer, whereas on long routes both<br />
these aids are required and perhaps<br />
also some equalizer boards. The aim of<br />
the equalization is that the residual deviation<br />
curve for the route shall be within<br />
the limits of ±1 dB re<strong>com</strong>mended<br />
byCCITT.<br />
Fault location<br />
Faulty line repeater<br />
It must be possible to locate a faulty line<br />
repeater rapidly and easily. For this purpose<br />
each repeater has been equipped<br />
with a simple crystal oscillator that generates<br />
an individual identification frequency,<br />
which is fed into both directions<br />
of transmission. The presence of<br />
the frequency can be checked with a selective<br />
level meter in the receiving terminal,<br />
and only the frequencies that<br />
emanate from the line repeaters after<br />
the faulty one will then be obtained, fig.<br />
14. The fault location frequencies lie at<br />
intervals of 2 kHz in the band 3640-<br />
4000 kHz. This makes it possible to supervise<br />
180 line repeaters, which corresponds<br />
to a homogeneous section of<br />
280 km.<br />
If the distant terminal station is unmanned<br />
the in<strong>com</strong>ing fault location frequencies<br />
can be looped there and<br />
double modulated with the frequencies<br />
7400 and 7220 kHz and then sent back.<br />
Half the available band is then used, i.e.<br />
frequencies that lie in the band 3820-<br />
4000 kHz are shifted to 3640 -3820 kHz,<br />
whereby both transmission directions<br />
can be supervised from one and the<br />
same terminal.<br />
Another way of using the looping equipment<br />
is to send the modulated frequencies<br />
on in the same direction. A general<br />
equipment for supervision of the fault<br />
location frequencies has been developed<br />
for the 4, 12 and 60 MHz systems.<br />
Cable break<br />
The power feeding of the line repeaters<br />
is cut off immediately if the cable is<br />
broken, and thus the fault location<br />
Fig. 15<br />
Location of a cable break. The amount of current<br />
fed out indicates where along the route the break<br />
has occurred
35<br />
oscillators also cease operating. In order<br />
to find the break the output current<br />
from the remote power feeding unit is<br />
measured when a constant voltage of<br />
600 V is supplied to the line from this<br />
unit. Each line repeater contains a highohmic<br />
resistor between the two transmission<br />
directions, through which a<br />
small amount of current can flow. The<br />
current measuring instrument in the remote<br />
power feeding unit has a special<br />
scale for measuring this current. When<br />
installing the system it is easy to calibrate<br />
and obtain the scale readings that<br />
correspond to the different line repeaters,<br />
fig. 15.<br />
Mechanical construction<br />
and installation<br />
As may be seen from fig. 16 there is<br />
space in one bay for two <strong>com</strong>plete systems.<br />
Each system consists of a line terminating<br />
shelf stack, a terminal repeater,<br />
a remote power feeding unit and a<br />
mains rectifier. The bay also contains a<br />
speaker circuit shelf that is <strong>com</strong>mon for<br />
the two systems. The shelves are in the<br />
M4 construction practice and the width<br />
of the bay is 600 mm.<br />
The line repeater is of the same mechanical<br />
design as in the other systems<br />
in the new generation. It consists of a<br />
small die-cast aluminium box with the<br />
dimensions 130x210x310 mm including<br />
the handle 4 .<br />
The line repeaters are installed in a<br />
waterproof cylindrical steel housing,<br />
which is buried in the ground or placed<br />
in a manhole. One of the types supplied<br />
by LM Ericsson holds three systems and<br />
this housing has a height of 750 mm and<br />
a diameter of 510 mm. When the line repeater<br />
is to be insulated from earth it is<br />
provided with an external case, fig. 17.<br />
This case is also used to absorb strong<br />
vibrations, which can occur when the<br />
cable is laid along motorways or railways.<br />
The line repeaters are easy to install if<br />
they are correctly equipped beforehand.<br />
This means that they are provided with<br />
— suitable gain<br />
— a crystal for the fault location<br />
— if necessary a line building-out network.<br />
Out in the field it is then only necessary<br />
Fig. 16<br />
60 MHz terminal bay<br />
The equipment for a fully equipped system is<br />
shown<br />
TR Terminal repeater<br />
LT Line termination<br />
PFU Remote power feeding unit<br />
SCS Speaker circuit shelf<br />
FLS Fault location shelf<br />
MR Mains rectifier<br />
opt Optional<br />
Fig. 17<br />
The cover for the line repeater, intended to<br />
Insulate it from earth and protect it from vibrations
Fig. 18<br />
The trial route, consisting of one line terminal,<br />
8 non-regulating and 2 regulating line repeaters<br />
and one cable equivalent<br />
Fig. 19<br />
Residual deviation curve before and after<br />
equalization<br />
pWOp/km<br />
Fig. 20<br />
Noise load curves for the line including the<br />
terminal<br />
Fig. 21<br />
The maximum variation of the residual deviation<br />
curve when the feeding current was varied by<br />
±10 mA and ±20 mA in relation to 290 mA<br />
to connect the repeaters to the relevant<br />
cable box in the steel housings.<br />
Trial route<br />
During the spring of 1977 a system trial<br />
was carried out on a route in the vicinity<br />
of Rome, where coaxial pairs<br />
were kindly provided by the Italian tele<strong>com</strong>munications<br />
administration ASST.<br />
System measurements were carried out<br />
in close collaboration by FATME and<br />
SIELTE, both members of the Ericsson<br />
Group, and LM Ericsson. The results<br />
were presented to ISPT, the State Institute<br />
for Post and Tele<strong>com</strong>munications,<br />
and to ASST, who also carried out measurements<br />
of their own.<br />
The trial route was equipped with a terminal<br />
bay and ten line repeaters, of<br />
which two were regulating. A system line<br />
with a length of 32 km was obtained by<br />
loop connection through a cable equivalent<br />
at the last line repeater, fig. 18.<br />
This length is sufficient in order to be<br />
able to check, by means of measurements,<br />
that the system functions satisfactorily<br />
and in accordance with the set<br />
design objectives. That this was so was<br />
also confirmed by the measurements<br />
that were carried out. It was easy to<br />
adjust the residual deviation curve to<br />
within ±1 dB with only the fixed equalizers,<br />
fig. 19.<br />
Noise measurements carried out on the<br />
whole system show good results. With<br />
a load of (-15dBmO/channel, the noise<br />
measured in the worst channel was 1.5<br />
pWOp/km, which is well below the value<br />
of 3 pWOp/km re<strong>com</strong>mended by CCITT.<br />
The measured load curves also show a<br />
good margin against overload, see fig.<br />
20.<br />
The dependence of the level stability on<br />
variations in the feeding current was<br />
very small. This was established by measuring<br />
the residual deviation curve for<br />
various values of this current within the<br />
range 270 mA to 310 mA. Fig. 21 shows<br />
that only very small level deviations were<br />
found.<br />
The hum modulation was measured by<br />
superposing an alternating current on<br />
the constant direct current provided by<br />
the remote power feeding unit, and then<br />
changing the amplitude and frequency<br />
of the alternating current. High values<br />
of hum modulation attenuation were<br />
then obtained, fig. 22, which was partly<br />
expected in view of the feeding principle<br />
that had been chosen for the line<br />
repeaters, see fig. 5.<br />
The crystal filters for suppressing the<br />
regulating pilots provide high attenuation<br />
at the pilot frequency and a sharp<br />
cut-off, which is illustrated in fig. 23.<br />
Other measurements carried out were<br />
— attenuation of the near-end and farend<br />
crosstalk<br />
— supervision with fault location frequencies<br />
— simulation of a cable break<br />
— the dependence of the level stability<br />
on variations of the battery voltage.<br />
The results of these measurements are<br />
not given here, but all were satisfactory.<br />
The level stability as a function of the<br />
cable temperature was not checked, because<br />
the cable for the trial was buried<br />
at a considerable depth. In view of both<br />
the short route and the limited trial period<br />
no marked variations could be expected.<br />
Fig. 22<br />
Hum modulation attenuation measured for alternating<br />
currents of different amplitudes and frequencies<br />
superposed on the feeding current<br />
5 mA<br />
8 mA<br />
12mA
Technical data<br />
Electrical data<br />
Cable<br />
2.6/9.5 mm<br />
Section length with a mean cable temperature ot + 10°C<br />
1.55 km<br />
Transmission band<br />
3640-61160 kHz<br />
Number of telephony channels 10800<br />
Gain at 61160 kHz, variable in stepsofl dB<br />
28.5+3 dB<br />
Main regulating pilot<br />
61160 kHz<br />
Extra pilots<br />
22372 and 4287 kHz<br />
Pilot level<br />
-1OdBm0<br />
Regulation range at the respective pilot frequencies<br />
±3 dB<br />
Line building-out networks, variable in steps of 2 dB<br />
0-22 dB<br />
Fault location frequencies<br />
at intervals of 2 kHz in the band<br />
3640-4000 kHz<br />
level of each such frequency<br />
-30dBmO<br />
Harmonic ratio attenuation measured at 0 dBm:<br />
2nd order at 4 MHz<br />
>97dB<br />
3rd order at 60 MHz<br />
>108dB<br />
Noise, for the system loaded with -15 dBmO/channel<br />
100 dB<br />
Remote power feeding unit, PFU<br />
voltage<br />
20-1200 V<br />
constant direct current<br />
290 mA<br />
Mains rectifier, maximum output power<br />
440 W<br />
37<br />
The system fed from<br />
station battery mains rectifier<br />
Max. number of linerepeatersperPFUwitheveryfourthregulating 47 40<br />
Corresponding distance between power-feeding stations 147 km 126 km<br />
Mechanical data<br />
Bay<br />
Line repeater, incl. handle<br />
Housing for 3 systems<br />
600x225x2600 mm<br />
130x210x310 mm<br />
height 750 mm<br />
diameter 510 mm<br />
Summary<br />
The results of the different measurements<br />
carried out on the trial route<br />
show that the equipment meets all demands<br />
made on it, which was evidenced<br />
not least by the fact that CCITT re<strong>com</strong>mendations<br />
were met with good margins.<br />
In this connection it is deserving<br />
of mention that the close cooperation<br />
between FATME and LM Ericsson has<br />
been of inestimable value both as regards<br />
the development of different<br />
parts of the system and the execution<br />
of measurements on the trial route, and<br />
also the production of line repeaters<br />
and other units included in the system.<br />
Fig. 23<br />
Attenuation of the main regulating pilot 61160 kHz<br />
in the receive direction of the line terminal<br />
References<br />
1. Ernbo, A.: Coaxial Cable for High<br />
Frequency Tele<strong>com</strong>munication<br />
Systems. Ericsson Rev. 5) (1974):3,<br />
pp 70-79.<br />
2. Englund, N.-G.: Coaxial Cable Systems:<br />
Operational Experience and<br />
Future Prospects. Ericsson Rev. 57<br />
(1974):1, pp. 13-20.<br />
3. Kallgren, O.: A New Generation of<br />
Line Systems for Small-Core and<br />
Normal Coaxial Cables. Ericsson<br />
Rev. 51 (1974):2, pp. 48-53.<br />
4. Breuer, H.-J.: Line Amplifier ZGC<br />
201 for 12 MHz Systems. Ericsson<br />
Rev. 57 (1974):2, pp. 54-60<br />
5. Manes, L. and Pausini, F.: A New<br />
Generation of Repeaters for Coaxial<br />
Cables. Not. teen. FATME No. 18,<br />
June 1976.<br />
6. Rydbeck, N.: Intermodulation Distortion<br />
for a 12 MHz Carrier Frequency<br />
System-Comparisons between<br />
Theory and Practice. Ericsson<br />
Tech. 32 (1976):2, pp.145-172.
Do the Media Understand<br />
Tele<strong>com</strong>munications<br />
Christopher Lorenz<br />
ERICSSON REVIEW plans to publish from time to time articles of a general interest<br />
in the field of <strong>com</strong>munications.<br />
The second article in this new series has been written by CHRISTOPHER LORENZ<br />
of the Financial Times in London, who is one of the best respected tele<strong>com</strong>munications<br />
writers in the world press today.<br />
Mr. Lorenz discusses some of the problems of the "unknown" tele<strong>com</strong>munications<br />
industry and the lack of recognition for what this industry contributes. And<br />
suggests that one of the solutions might be education and information of mass<br />
media as a means of improving the general public's understanding of tele<strong>com</strong>munications.<br />
achieved high levels of telephone penetration,<br />
and are trying to improve the<br />
usage of their installed assets.<br />
Greater understanding from the public<br />
can also help the organisation in other<br />
ways, such as reducing the barrage of<br />
impatience and <strong>com</strong>plaint when something<br />
goes wrong. This applies as much<br />
to the occasional breakdown as to the<br />
impact of changing levels of telephone<br />
network investment on employment in<br />
the factories which make tele<strong>com</strong>munications<br />
equipment.<br />
UDC 654.1:<br />
659.3<br />
Many a tele<strong>com</strong>munications professional<br />
has asked me over the years why his<br />
industry is so poorly understood by the<br />
general public, as <strong>com</strong>pared with motor<br />
vehicles or shipbuilding-or even<br />
more "difficult" subjects such as<br />
nuclear power, genetic engineering or<br />
astro-physics. After all, he usually argues,<br />
tele<strong>com</strong>munications is of prime<br />
social and economic importance.<br />
A mass of factors supports his argument:<br />
efficient telephone and data networks<br />
are vital to the very life of a modern<br />
industrialised economy; operation<br />
of the systems and their manufacture<br />
together employ several hundred thousand<br />
people in each of many countries<br />
round the world; massive annual investment<br />
in the business is required (often<br />
running into several billions of dollars);<br />
taken together with associated activities<br />
like <strong>com</strong>puting and electronic <strong>com</strong>ponents,<br />
tele<strong>com</strong>munications will account<br />
for more than six per cent of several<br />
gross national products in Europe by<br />
the early 1980s; and on the question of<br />
technological innovation, the tele<strong>com</strong>s<br />
man will argue that current advances in<br />
both switching and transmission are as<br />
exciting as anything the motor industry<br />
or even nuclear power have to offer.<br />
This concern with the need for greater<br />
public understanding is not just a question<br />
of giving the tele<strong>com</strong>s professional<br />
the widespread recognition he deserves,<br />
alongside the designer of cars, or<br />
nuclear physicist. In almost every country,<br />
greater public awareness could promote<br />
demand for all sorts of telephone<br />
services —an important economic factor<br />
to countries which are now installing<br />
extensive networks for the first time,<br />
just as it is for those which have already<br />
If administrations and manufacturers<br />
are to get their message across, they<br />
will first have to persuade the media<br />
(both press and broadcasting) that they<br />
are in an interesting business. This will<br />
be<strong>com</strong>e harder in the next few years, as<br />
more and more equipment is <strong>com</strong>pressed<br />
into obscure small boxes of integrated<br />
circuits controlled by <strong>com</strong>puter<br />
tapes and discs. Even with traditional<br />
technology, it is not an easy task.<br />
From a journalistic point of view, the<br />
most obvious problem about the telephone<br />
is that, in many countries, people<br />
perceive it as "just part of the furniture".<br />
It has been around for so long that it<br />
has ceased to be an interesting object<br />
for many people —unless it breaks<br />
down, that is.<br />
In the United States, to some extent,<br />
the telephone has been given a new<br />
lease of life as an object of public interest<br />
by the advent of <strong>com</strong>petition since<br />
1968 in parts of the tele<strong>com</strong>munications<br />
market. People's interest can hardly fail<br />
to be aroused when they are assaulted<br />
daily by the <strong>com</strong>peting claims of various<br />
suppliers, and when their local shopping<br />
plaza contains at least one "Phone<br />
Mart" with a bewildering array of handsets<br />
in over a dozen colours. The <strong>com</strong>petitive<br />
climate and the general public<br />
awareness it creates, stimulates the media<br />
to give tele<strong>com</strong>munications considerable<br />
"coverage".<br />
In Europe, by contrast, the media still<br />
generally turns its attention to tele<strong>com</strong>munications<br />
only when it is the subject<br />
of a major row, be this over the threatened<br />
admission or nationalisation of<br />
new suppliers (as in France and the<br />
United Kingdom in recent years), or the
39<br />
CHRISTOPHER LORENZ<br />
Financial Times<br />
London<br />
latest cut in Post Office orders —and<br />
therefore inevitable unemployment in<br />
the suppliers' factories. It is significant,<br />
for example, that many national newspapers<br />
in Europe have virtually ignored<br />
the major underlying reason for repeated<br />
rundowns in suppliers' labour<br />
forces: the shift from labour-intensive<br />
electro-mechanical switching to semielectronics.<br />
Instead, they have concentrated<br />
on the spate of downward revisions<br />
in Post Office equipment orders.<br />
This is the drama of which popular journalism<br />
is made, but it usually oversimplifies<br />
any situation to the extent of<br />
damaging distortion. It also misses the<br />
chance to produce a fascinating study<br />
of a major industry undergoing a <strong>com</strong>plete<br />
change in character.<br />
There are other, more constructive<br />
ways in which the media could be encouraged<br />
to "cover" tele<strong>com</strong>munications".<br />
For the writer, tele<strong>com</strong>munications<br />
consumption of national budget<br />
resources can be made an interesting<br />
theme (whether you think it is too large<br />
or too small). So can the efficient management<br />
of the tele<strong>com</strong>munications<br />
administrations. PTTs are some of the<br />
largest employers in many countries,<br />
too, but how many people understand<br />
how they go about their <strong>com</strong>plex business<br />
The social aspect of developments in<br />
tele<strong>com</strong>s provide another obvious<br />
wealth of interesting material, whether<br />
in developing countries (basic telephony<br />
as well as prestigious satellite projects),<br />
or in the industrialised world. Here, one<br />
should not need to repeat the well-worn<br />
futuristic cliches about "working from<br />
home" or "the wired city" in order to<br />
provoke interest. Special services for<br />
handicapped people, or telephone audio<br />
conferencing (including its energysaving<br />
aspects) are down-to-earth<br />
examples.<br />
To the engineer, these themes may<br />
seem too lightweight, especially if his<br />
<strong>com</strong>plaint is addressed more towards<br />
the lack of public understanding about<br />
the technological progress in which he<br />
is so closely involved, and which he may<br />
soon want to market in a new service.<br />
Of all the current examples, only videoconferencing<br />
has attracted widespread<br />
popular coverage by the media in a<br />
number of countries (this includes the<br />
view- or picture-phone). Electronic<br />
switching, waveguides and even optical<br />
fibres have received little more than the<br />
occasional mention in most general<br />
newspaper (my own is an exception).<br />
It is often impossible to write about an<br />
economic or organisational aspect of<br />
tele<strong>com</strong>munications without getting<br />
deeply into technological issues. Unless<br />
the journalist explains the technical<br />
principles and carrying capacity of optical<br />
fibres, for instance, he cannot hope<br />
to convey how important they may be in<br />
cutting transmission costs, providing<br />
greater bandwith, and therefore offering<br />
subscribers a whole new range of services<br />
at reasonable prices. But this need<br />
to use technology as a "lever" can be<strong>com</strong>e<br />
a barrier to writing about tele<strong>com</strong>munications<br />
at all.<br />
This is the crux of the problem. Many<br />
people—including some newspaper<br />
editors-are quite simply scared off by<br />
technology, some by the word itself,<br />
others by its <strong>com</strong>plex (and sometimes<br />
disturbing) implications. Many editors<br />
also have an unfortunate habit of underrating<br />
the intelligence of their public.<br />
This <strong>com</strong>pounds the problem facing a<br />
<strong>com</strong>pany or organisation which is trying<br />
to popularise tele<strong>com</strong>munications.<br />
A recent television programme about<br />
telephony is an ideal example here.<br />
Much of it consisted of pictures of workmen<br />
erecting telephone poles in beautiful<br />
countryside, though the programme<br />
had nothing directly, to do with the environmental<br />
effects of technology. Quite<br />
rightly, many tele<strong>com</strong>munications professionals<br />
were extremely disappointed<br />
by the film.<br />
Its short<strong>com</strong>ings were partly explained<br />
by the fact that shots of people at work<br />
are easier and cheaper to take than<br />
those of technological equipment or<br />
processes. But the programme makers<br />
also assumed that viewers prefer watching<br />
objects they can immediately indentify,<br />
rather than those which are unfamiliar.<br />
Telephone exchange equipment<br />
is an obvious problem here.<br />
The film-makers also felt that switching<br />
equipment could not be made visually<br />
interesting unless large parts of it were
40<br />
seen to move. So they were forced to go<br />
along to one of the oldest Strowger exchanges<br />
they could find. Even then,<br />
they had to persuade the exchange's<br />
entire staff to dial each other for minutes<br />
on end, in order to set enough of<br />
the switches moving and clattering!<br />
Another possible problem was the current<br />
fashion in television for "allowing<br />
the pictures to tell the story", rather<br />
than gathering experts in a studio or on<br />
location to discuss it. "Talking heads"<br />
(as such expert discussions are called<br />
in the trade) are all but banned by the<br />
editors of some TV programmes. This<br />
attitude militates strongly against the<br />
coverage of <strong>com</strong>plex industrial subjects,<br />
and in favour of riots, natural disasters<br />
and the like.<br />
Even where such fashions carry little<br />
weight, there are other problems. A different<br />
TV station took the ambitious<br />
step of making a general-interest programme<br />
about the impact of microprocessors<br />
on a wide range of industry.<br />
The staff immediately faced the problem<br />
of filming something as small and static<br />
as a tiny chip of silicon without incurring<br />
the high cost of microscopic pictures<br />
and of effectively covering at the<br />
same time the changes in strategy being<br />
forced in industry by the new technology.<br />
For some viewers, the pictures<br />
appearing on the screen of microcircuit<br />
manufacture and <strong>com</strong>puter assembly<br />
were irrelevant to the ac<strong>com</strong>panying<br />
discussion of the industrial strategy<br />
issues; the pictures were described by<br />
some of the staff themselves as "wallpaper"<br />
against which to set the words<br />
of <strong>com</strong>mentary. The industrial issues, in<br />
turn, were difficult to explain without a<br />
mass of charts and "talking heads".<br />
These two television programmes were<br />
unusual in that they tried to make a serious<br />
examination of the issues surrounding<br />
generally unfamiliar technologies.<br />
The second was far more successful<br />
than the first, even though<br />
microprocessors are more difficult to<br />
handle than tele<strong>com</strong>munications in visual<br />
terms. There were a few distortions<br />
of detailed fact but at least the electronics<br />
engineers could be thankful that<br />
they were minor.<br />
One only needs to consider nuclear<br />
power to get a very different storymore<br />
than any other form of high technology,<br />
it is always "news" for the TV<br />
and newspapers. No nuclear physicist<br />
can claim that his work is ignored by the<br />
media. Instead, he will <strong>com</strong>plain about<br />
distortion and about "environment correspondents"<br />
whose business seems<br />
often to consist solely of spreading<br />
gloom and doom.<br />
Tele<strong>com</strong>munications can hardly be presented<br />
as physically dangerous, so it<br />
should always be spared such an extreme<br />
type of bad press. All the same<br />
considerable ingenuity will be required<br />
from the industry itself, as well as the<br />
media, if the issues are to be presented<br />
accurately, but in a way the public can<br />
understand.<br />
There is, I think, a case for both tele<strong>com</strong>munications<br />
administrations and<br />
manufacturers to devote close attention<br />
to the education and information of the<br />
media. Tele<strong>com</strong>munications will never<br />
be well understood by the public unless<br />
the media understand it first.
The Ericsson Group<br />
With associated <strong>com</strong>panies and representatives<br />
EUROPE<br />
SWEDEN<br />
Stockholm<br />
1. Telefonaktiebolaget LM Ericsson<br />
2. LM Ericsson Telemateriel AB<br />
1, ABRifa<br />
1. Sieverts Kabelverk AB<br />
1. Svenska Radio AB<br />
5. ELLEMTELUtvecklings AB<br />
1. AB Transvertex<br />
4. Svenska Elgrossist AB SELGA<br />
1. Kabmatik AB<br />
4. Holm & Encsons Elektnska AB<br />
4. Mellansvenska Elektnska AB<br />
4. SELGA Mellansvenge AB<br />
Allngsfis<br />
3. Kabeldon AB<br />
Gavle<br />
2. Vanadis Entreprenad AB<br />
Gothenburg<br />
4. SELGA Vastsvenge AB<br />
Kungsbacka<br />
3. Bota Kabel AB<br />
Malmo<br />
3. Bjurhagens Fabnkers AB<br />
4. SELGA SydsvengeAB<br />
Norrkoping<br />
3. AB Norrkopings Kabelfabrik<br />
4. SELGA Ostsvenge AB<br />
Nykoplng<br />
1. Thorsman & Co AB<br />
Sundsvall<br />
4. SELGA Norrland AB<br />
Vaxjo<br />
1. Widells Metallprodukter AB<br />
EUROPE (excluding<br />
Sweden)<br />
BELGIUM<br />
Brussels<br />
2. Ericsson Belgium sa/nv<br />
DENMARK<br />
Copenhagen<br />
2. LM Ericsson A/S<br />
1. Dansk Signal Industri A/S<br />
3. GNT AUTOMATIC A/S<br />
1. I. Bager& Co A/S<br />
2. LM Ericsson Radio ApS<br />
Tastrup<br />
2. Thorsman & Co ApS<br />
FINLAND<br />
Helsinki<br />
2. Oy Thorsman & Co Ab<br />
Jorvas<br />
1. Oy LM Ericsson Ab<br />
FRANCE<br />
Colombes<br />
3. Societe Francaise des<br />
Telephones Ericsson<br />
Boulogne sur Mer<br />
1. RIFA S A<br />
Marseille<br />
4. Etablissements Ferrer-Auran S A<br />
IRELAND<br />
Athlon e<br />
1. LM Ericsson Ltd<br />
Drogheda<br />
2. Thorsman Ireland Ltd<br />
ITALY<br />
Rome<br />
1. FATME Soc. per Az<br />
1. Scarfini Soc per Az<br />
5. SETEMER Soc. per Az<br />
2. SIELTE Soc. per Az.<br />
The NETHERLANDS<br />
Rijen<br />
1. Ericsson Telefoonmaatschappj] B.v.<br />
NORWAY<br />
Nesbru<br />
3. A/S Elektrisk Bureau<br />
3 United Marine Electronics A/S<br />
Oslo<br />
2. SRA Radio A/S<br />
2. Thorsman & Co A/S<br />
4. A/S Telesystemer<br />
4. A/S Installator<br />
Drammen<br />
3. A/S Norsk Kabelfabrik<br />
POLAND<br />
Warszaw<br />
7. Telefonaktiebolaget LM Ericsson<br />
PORTUGAL<br />
Lisbon<br />
2. Sociedade Ericsson de Portugal Lda<br />
SPAIN<br />
Madrid<br />
1. Industnas de Tele<strong>com</strong>unicaci6n S A<br />
(Intelsa)<br />
1. LM Ericsson S A<br />
SWITZERLAND<br />
Zurich<br />
2. Ericsson AG<br />
UNITED KINGDOM<br />
Chorley<br />
2. Thorsman & Co (UK) Ltd<br />
Horsham<br />
4. Thorn-Ericsson Tele<strong>com</strong>munications<br />
{Sales) Ltd<br />
3. Thorn-Ericsson Tele<strong>com</strong>munications<br />
(Rentals) Ltd<br />
5. Swedish Ericsson Company Ltd<br />
3. Thorn-Ericsson Tele<strong>com</strong>munications<br />
(Mfg) Ltd<br />
6 Thorn-Ericsson Tele<strong>com</strong>munications<br />
Ltd<br />
London<br />
4. United Marine Leasing Ltd<br />
4. United Marine Electronics (UK) Ltd<br />
WEST GERMANY<br />
Frankfurt-am-Main<br />
2. Rifa GmbH<br />
Hamburg<br />
4. UME Marine Nachnchtentechnik, GmbH<br />
Hanover<br />
2. Ericsson Centrum GmbH<br />
Ludenscheid<br />
2. Thorsman & Co GmbH<br />
Representatives in:<br />
Austria. Greece, Iceland, Luxembourg,<br />
Yugoslavia.<br />
LATIN AMERICA<br />
ARGENTINA<br />
Buenos Aires<br />
1. Cia Ericsson S A.C.I<br />
1. Industnas Electncas de Quilmes S A<br />
5. Cia Argentina de Telefonos S A.<br />
5. Cia Entrernana de Telefonos S.A<br />
BOLIVIA<br />
La Paz<br />
7. Telefonaktiebolaget LM Ericsson<br />
BRAZIL<br />
Sao Paulo<br />
1. Ericsson do Brasil Comercio e<br />
Industna S.A<br />
4. Sielte S.A. Instalacdes Eletncas e<br />
Telefonicas<br />
4. TELEPLAN, Projetos e Planejamentos<br />
de Tele<strong>com</strong>mumcacoes S A<br />
Rio de Janeiro<br />
3. Fios e Cabos Plasticos do<br />
Brasil S.A.<br />
Sao Jose dos Campos<br />
1. Tele<strong>com</strong>ponentes Comercio e<br />
Industria S.A.<br />
CHILE<br />
Santiago<br />
2. Cia Ericsson de Chile S.A.<br />
COLOMBIA<br />
Bogota<br />
1. Ericsson de Colombia S.A<br />
Cali<br />
1. Fabricas Colombianas de Materiales<br />
Electncos Fa<strong>com</strong>ec S.A.<br />
COSTA RICA<br />
San Jose<br />
7. Telefonaktiebolaget LM Ericsson<br />
ECUADOR<br />
Quito<br />
2. Telefonos Ericsson C A<br />
GUATEMALA<br />
Guatemala City<br />
7. Telefonaktiebolaget LM Ericsson<br />
Port-au-Prince<br />
7. LM Ericsson<br />
MEXICO<br />
Mexico OF<br />
1. Teleindustna Ericsson. S A<br />
1. Latmoamencana de Cables S A.<br />
deC V<br />
2. Telefonos Ericsson S A<br />
2. Telemontaie, S A de C V<br />
PANAMA<br />
Panama City<br />
2. Telequipos S A<br />
7. Telefonaktiebolaget LM Ericsson<br />
PERU<br />
Lima<br />
2. Cia Ericsson S A<br />
EL SALVADOR<br />
San Salvador<br />
7. Telefonaktiebolaget LM Ericsson<br />
URUGUAY<br />
Montevideo<br />
2. Cia Ericsson S A<br />
VENEZUELA<br />
Caracas<br />
1. Cia An6nima Ericsson<br />
Representatives in:<br />
Bolivia, Costa Rica, Dominican Republic,<br />
French Guiana, Guadeloupe, Guatemala,<br />
Guyana, Honduras, Martinique, Netherlands<br />
Antilles, Nicaragua. Panama, Paraguay. El<br />
Salvador, Surinam. Trinidad, Tobago.<br />
AFRICA<br />
ALGERIA<br />
Algiers<br />
7. Telefonaktiebolaget LM Ericsson<br />
EGYPT<br />
Cairo<br />
7. Telefonaktiebolaget LM Ericsson<br />
LIBYA<br />
Tripoli<br />
7. Telefonaktiebolaget LM Ericsson<br />
TUNISIA<br />
Tunis<br />
7. Telefonaktiebolaget LM Ericsson<br />
ZAMBIA<br />
Lusaka<br />
2. Ericsson (Zambia) Limited<br />
2. Telefonaktiebolaget LM Ericsson<br />
Installation Branch<br />
Representatives in:<br />
Angola, Benin, Botswana. Cameroon, Central<br />
African Empire, Chad, Congo, Egypt.<br />
Ethiopia, Gabon. Ivory Coast, Kenya, Liberia.<br />
Libya, Madagaskar, Malawi, Mali, Malta.<br />
Mauretama, Morocco, Mozambique. Namibia.<br />
Niger, Nigeria. Republic of South Africa.<br />
Reunion, Senegal, Sudan, Tanzania, Togo.<br />
Tunisia, Uganda. Upper Volta, Zaire.<br />
ASIA<br />
Calcutta<br />
2. Ericsson India Limited<br />
INDONESIA<br />
Jakarta<br />
2. Ericsson Telephone Sales<br />
Corporation AB<br />
Baghdad<br />
7. Telefonaktiebolaget LM Ericsson<br />
IRAN<br />
Teheran<br />
2. Ericsson Telephone Sales<br />
Corporation AB<br />
3. Simco Ericsson Ltd.<br />
4. Aktiebolaget Enfon<br />
KUWAIT<br />
Kuwait<br />
7. Telefonaktiebolaget LM Ericsson<br />
LEBANON<br />
Beirouth<br />
2. Societe Libanaise des Telephones<br />
Ericsson<br />
MALAYSIA<br />
Shah Alam<br />
1. Ericsson Tele<strong>com</strong>munications<br />
Sdn Bhd<br />
OMAN<br />
Muscat<br />
7. Telefonaktiebolaget LM Ericsson<br />
SAUDI ARABIA<br />
Riyadh<br />
7. Telefonaktiebolaget LM Ericsson<br />
Bangkok<br />
2. Ericsson Telephone Corporation<br />
Far East AB<br />
Ankara<br />
2. Ericsson Turk Ticaret Ltd Sirketi<br />
Representatives in:<br />
Bahrein, Bangladesh. Burma. Cyprus. Hong<br />
Kong, Indonesia. Iran, Iraq, Jordan, Kuwait,<br />
Lebanon, Macao, Nepal, Oman, Pakistan,<br />
Philhppines, Qatar, Saudiarabia, Singapore,<br />
Sri Lanka, Syria, United Arab Emirates.<br />
UNITED STATES and<br />
CANADA<br />
UNITED STATES<br />
Woodbury NY.<br />
2. LM Ericsson Tele<strong>com</strong>munications Inc<br />
New York, NY.<br />
5. The Ericsson Corporation<br />
CANADA<br />
Montreal<br />
2. LM Ericsson Ltmitee/Limited<br />
AUSTRALIA and<br />
OCEANIA<br />
Melbourne<br />
1. LM Ericsson Pty Ltd<br />
1. Rifa Pty Ltd.<br />
5. Teleric Pty Ltd<br />
5. LM Ericsson Finance Pty, Ltd<br />
Sydney<br />
3. Conqueror Cables Ltd<br />
Representatives in:<br />
New Caledonia, New Zealand. Tahiti<br />
1. Sales <strong>com</strong>pany with manufacturing<br />
2. Sales and installation <strong>com</strong>pany<br />
3. Associated sales <strong>com</strong>pany with manufacturing<br />
4. Associated <strong>com</strong>pany with sales and<br />
installation<br />
5. Other <strong>com</strong>pany<br />
6. Other associated <strong>com</strong>pany<br />
7. Technical office
TELEFONAKTIEBOLAGET LM ERICSSON<br />
ISSN 0014-0171 Printed in Sweden L/ungforetagen, Orebro 1978