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TELEPHONE INFORMATION SYSTEMS AND ASSOCIATED
TRAFFIC THEORY PROBLEMS
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Heinz Schwartzel
Siemens A. G.
Munich, Federal Republic of Germany
ABSTRACT
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In the telephone information system, telephones
and videophones serve as input/output devices
to the computer; the switching centers interoperate with computers. As a result, these systems
offer more extensive communication facilities.
Over and above the exchange of information between humans, they permit · an exchange of information between man and computer. Using the
block structure of such a system for illustration,
related traffic theory questions are raised:
characteristics of the data-telephone traffic,
performance of data-intensive input/output
routines, performance of operating programs
for on-line multi-access organization. Two data
services are demonstrated: the ~ephone as a
desk calculator; information and orders per
telephone.
1. THE OBJECTIVES OF TELEPHONE INFORMATION
SYSTEMS
In matters concerning remote data processing
a distinction will be made in the future between two groups of users. The first group wi ll
comprise the professional users who work with
expensive and sophisticated terminals, e.g .
with data display sets and data printers.
During intensive dialogues on the basis of extensive input/output languages they
exchange large quantities of data with the
Qpmputers. The second group will consist of
the unprofesssional users who feed in only
occasionally data or call for information,
e.g. within the acquisition of service data
or by using simple information services. Generally, since these dialogues are simple, these
users do not require sophisticated terminals,
but rather simple and inexpensive ones which
can be installed in large quantities. Because
of the growing use of application-oriented
computers, they will request access to
different computers, depending on the problem.
To solve transmission and SW-itching problems,
switching networks can be used including the
telephone terminals and the switching centers.
When there is a clear interface from the point
of view of equipment and organizati<;m, the
processing and exob.ange of informatlon oonverges i
to a single task.
As telephones and videophones are opened up
for use as data terminals, the possibilities
of information exchange are extended. Communication between humans is joined by communication between man and computer via the same
terminals.
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2. BLOCK STRUCTURE AND COORDINATING PROCEDURES
Apart from telephoning, telephone information
systems help to solve the two following data
tasks:
2.1. Data acquisition with concentration on
off-line data media or on-line to the
computer which follows.
2.2. Information exchange as a short dialogue '
with the computer
These tasks arise first and foremost in large
administations and business concerns, that
is, in places where a PABX is used. Figure 1
shows the block structure of a telephone information system. Three components can be
distinguished:
a. The terminals - represented by push butt on
telephones, videophones and data printers.
b; The switching system with ways out to the
data concentrator and/or the computer which
follows.
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c. The computer - (or the data concentrator,
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3. TRAFFIC THEORY PROBLEMS
designed as a small computer) - with the
technical equipment for remote ~at~ ~ro­
cessing (line multiplexers and ~nd~v~dual
buffers corresponding to the types of terminals) with operating systems for "online muitiaccess processing" and with user
programs.
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The traffic theorist is faced with a series
of problems.
3.1. Traffic characteristics
In telephone information systems, both telephone and data traffic are handled. The characteristics of telephone traffic are known,
while those of data traffic with the computer
are still largely unknown. The results ~f.
systematic traffic measurements on spec~f~c
systems are not yet available. But it is
commonly expected that the mean holding time
of data traffic is substantially lower than
that of telephone traffic. This will be the
case with pure data acquistion systems. In
systems which permit a dialogue with the
computer, the dialogue procedures - some will
be dealt with more closely - will inf luence
the traffic characteristics in a way as yet
unknown.
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3.2. Planning data-intensive input/
output routines
·FIG.A: "BLOCK
STltUCTUR,E
INFOfl-MRiION
OFA TELEFONE
S'ISTEM
Now some comments on how connections are built
up and broken down, using the telephone as a
data terminal:
The inputs to the computer are rea?hed by one
or several call numbers. To establ~sh a connection the user first uses the pushbutton set.
He dials the computer, which answers with a
data tone. By subsequently diali~g other. digits
(suffix-dialing) he indicates wh~ch spec~~l .
user program he requires. These furth~r d7g~ts
serve as selection criteria to the operat~ng
system to load the user program and to assign
the user, the computer input and the user program. After the dialogue has begun, the pushbutton set serves the user as a mean of feeding in informations. The c~mputer answers.
audibly. For this purpose ~t controls a d~­
gital or analog voice unit via an output.
For the buildup and release of a data connection, a number of items of system information
are exchanged between the user, the telephone
switching system and the computer.
Figure 2 outlines the case described.
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FIG.~: coo'PERATING
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Corresponding to the block diagram as shown
in Fig. 1, on the computer side a series of
buffers, to be operated simultaneously, will
be used for voice output, video output, etc.
Their number will be fixed in accordance with
the amount of traffic to be handled. According
to the present technical state their supply
requires a high data rate of about 1200 to
2400 bits per second. Depending on the output
time of one element of information, the search
time on the external memory as the data medium
and the output routine, a certain number of
buffers can be operated simultaneously.
Fig ure 3, for example, shows the average
permissible number of vocoders depending on
the length of the voice element, the mean
search time on the external memory, and the
transmission speed from the external memory.
The output routine requires an output area in
the main memory which is at least as large as
the length o~ the voice element.
3.3. Planning Multi-Access Operating Systems
At every instant the computer must be ready
to be addressed by a terminal via the switching system, t .o prepare the user program which
has been called down, and to organize simultaneous use by several subscribers (time
sharing). This process raises all the problems
of program segmentation, pag i ng and timesharing, which are well known from the development of time-sharing computer systems.
When designing a pilot system we based ourselves on the following considerations: User
programs for short computer dialogues are
called up, supplied with data, and give out
answers. We thought we could risk letting the
programs which had been called up be transferred in coherent segments into the main
memory. A maximum of 16 segments can run in
multi-program processing. The main memory is
divided into units of 512 words. The program
segments comprise whole multiples of the main
memory units. The efficiency of the main
memory varies, depending on the calldown rate
of the programs, which are of varying lengths.
Figure 4 shows the result of simulations. As
realized in the pilot system, segments with a
length of 1, 2, 4
main memory units
occur with approximately the same frequency.
The utilization of the ma i n memory is shown
dependent on the traffic offered (in erlangs).
For the purpose of comparison, the corresponding values are given for the case when segment
INf=:ORI"IATION .5
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Figure 5 shows an example of the mas k technique. This meth od was performed for a
"telephone as desk calculator" user program
in the pilot system.
coherence is not required. The decrease in
utilizat i on as a result of the segment
coherence effect is very small •
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The third method also offers "good prospects.
If the letters are distributed with equal
probability amongst the digits there are in
fact some ambigu ities in the case of alphanumerical input, but they are few. Given
5000 terms with an average length of six
letters, the probability tha t at t he most
two terms will give the same c ombi nation of
digits is about 2 %. These f ew errors can be
eliminated by the computer using specific
checkbacks.
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The last method must "b e tailored to the
particular application. In our opinion the
dialogues will generally be "quite boring"
for the user.
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The following examples of use will be demonstrated:
a) The telephone as a desk-calculator
b) The telephone as an aid for information and
orders, using the example of a building
elements store.
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4. Dialogue procedures and demonstration
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Apart fr om the traffic theory problems there
is also the basic question: "How can a telephone informat i on systems be used efficiently? How can a meaningful d~alogue be conducted from the telephone wi th the computer?
Suitable dialogue p~ocedures must be developed. Some thoughts in this connection: The
pushbutton telephone has 10 keys for digit
input and 2 special keys. Our experiences so
far have shown that we need three functions
for controlling the dialogue - independent of
the specific case of application:
"
1. Erase a nd clear
2. Output repetit i on
3. Program change
and also the "end of input" function.
We have ass i gned thi s last function exclusively to the "red key". The first three are
reali zed by combinations of a "green key"
and a number key (always the numbers 7 - 9).
For informat i on input t he following methods
can be used:
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4.1 . Purely numerical-coding
LITERATUR
4.2. Non-ambiguous expans i on of the set of
meanings by using masks.
1 . B.Corby: IBM 2750, Voice and Data
Switching System:
Organization and Functions.
IBM J.Res.Develop. 13, 408 (1969)
4.3. Ambiguous expansion of the set of
meanings
2. H.Roder: Zur Entwicklung von FernsprechNebenstellenanlagen mit vollelektronischem Raumvielfach und zentralisierter
Logik
NTZ 22, Vol.8, 1969, p.437 ff.
4.4. Special computer-controlled dialogue
The purely numerical coding can be arranged
with format requirements and test digits in
such a way that errors can easily be recognized.
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3. D.v.Sanden: Datenverkehr liber FernsprechNebenstellenanlagen.
Fachvortrag anlaBlich der VDPI-Jahresversammlung 69 am 28.9.1969, Hannover,
Deutschland
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4. F.Fahrenschon, R.Jurk: Moglichkeiten des
Datenverkehrs in Fernsprech-Nebenstellenanlagen.
Siemens-Zeitschrift 43, 1969, Vol.4,
p. 338 ff.
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5. F.Fahrenschon, W.Strobelt: Datentechnik "in
Fernsprech-Nebenstellenanlagen.
Siemens-Zeitschrift 43 (1969), Beiheft
"Datenfernverarbei tung", p. 57 i f .
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6. M. Joseph: "An analysis of paging and program behaviour",
The Computer Journal Vol. 13, No.1 (Febr,70)
p. 48 ff.
7. H.Hellermann: Some principles of time sharing schedular strategies
IBM System Journal No. 2, 1969, p. 94 ff.
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8. V.L. Wallace, D.L. Mason: Degree of Multi-
programming in Page-on-Demand Systems
Comm. of the ACM, Vol. 12, No.- 6, June 69,
p. 305
9. B. Rondell: A Note on Storage Fragmentation
and Program Segmentation,
Comm. of the ACM, Vol. 12, No. 7, July 69,
p. 365 · ff.
10. Stemberger: tlber Namenseingabe durch das
Telefon
Mai 1969, interner Siemens-Bericht
11. G. Arndt: Informatione-Systeme mit digitaler Sprachausgabe ': tlber den Einsatz
externer GroSspeicher fUr die codierte
Sprache.
Erscheint in der NTZ
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12. H.Pilz, V.Konle: Datenverkehr Uber Fernsprech-Nebenstellenanlagen zum Bestellen
von Lagerartikeln
Siemens-Zeitschrift (1970) Vol. 4
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