Contents Telektronikk - Telenor

50
The life and work of Conny Palm
– some personal comments and experiences
BY ROLF B HAUGEN
This paper is an introduction to the life
and works of the great Swedish teletraffic
theoretician Conny Palm. The
focus is on how I personally have used
and experienced Palm’s work throughout
the years rather than trying to
make an exhausted review. Through
this flash back of my years of work in
teletraffic, it is unavoidable not to
mention a few other teletraffic researchers
that came into “my way”.
Nevertheless, the theme throughout
the paper is always Palm and his work.
1 Introduction
The science of Teletraffic theory, founded
by Erlang in the beginning of this century,
has always had a strong foothold in
Scandinavia. The field was first dominated
by the Danes, then gradually Swedish
groups became dominant, until finally,
on the threshold of the seventies, a relatively
strong build-up started in Norway.
By that time professor Arne Myskja and
his colleagues in Trondheim were engaged
in traffic measurements with subsequent
analyses and several interesting
studies of subscriber behavior. At
Kjeller, Richard Solem was busy building
up a scientific group at Norwegian
Telecom Research (NTR) with a rather
broad focus. The teletraffic group at
NTR, the T-group, was soon to be a force
centre in the Norwegian community, initiating
activities in Trondheim as well as
numerous places in Oslo, like the Norwegian
Computer Centre, STK, EB, other
departments of Norwegian Telecom, to
mention but a few.
Personally, I had the privilege to join the
Kjeller group in the middle of the seventies
after some years as ‘traveling’ physicist.
Coming from the University of Oslo
rather than from NTH as did the others in
the group, I was perhaps a bit of an outsider.
However, since we were all physicists
of one kind or another, I quickly fell
in with the professional as well as the
social activities in a fairly acceptable
way. And the atmosphere and activities
in the group were just incredible! It is
rare in any profession to meet so many
extraordinary gifted people in one and
the same group. The T-group soon
became a concept at the institute. Practical
jokes were numerous and legendary,
and in social activities like sports, games,
partying, etc., the challenge at NTR was
always: the T-group versus the rest! But
the professional flag was nevertheless
kept high!
Although my main fields of study were
physics and mathematics, I embarked on
a course in statistics, quite by impulse, at
one point during my studies. By chance, I
chose the subject Probability theory with
a text book written by William Feller, a
person unknown to me at that time. But
seldom have I been more fascinated! It
was obvious that Feller had practical
experience in the field of probability; his
examples and explanations were related
to real life situations. And his approach
and mathematical treatment of the problem
was done in such an intuitive way
that we hardly realized that we, in fact,
were working with the fundamentals of
the underlying theory. Even as a student I
grasped the freshness of his treatment
and was stricken by his pedagogic ability
in explaining intricate problems in a
simple way.
Feller brought me into the world of
stochastic processes, a world fascinating
in itself. But equally fascinating was
Feller’s treatment. I certainly remember
being introduced to the state equations,
the so called birth and death processes
based on equilibrium considerations.
Feller also introduced me to the generating
functions, a powerful means of solving
discrete processes. It was incredible
with which elegance and virtuosity Feller
solved intricate probability problems
with the help of these functions! At least,
so it seemed to me at that stage of my
education.
Hardly could I then know that later, and
for a long period of my life, I was to have
the above mentioned processes and solution
techniques as my daily work. I
remember vaguely that I was introduced
to the names Erlang and Palm; Erlang
being the person behind the state equations
that became the origin of queuing
theory, and Palm one of the pioneers in
establishing the mathematical fundament
of those theories. I also seem to remember
that some of the examples and solutions
in the text book went back to Palm.
Even if I at that time had no inclination
towards telecommunications, I certainly
grasped that Erlang had to do with telephony.
Palm’s background, though, was
more diffuse to me.
Another eight years were to pass before I
again ‘met’ with the two mentioned pioneers.
I had then started at NTR, read the
fundamentals of traffic theory and joined
a project team analyzing the telephone
network of Oslo, the so-called ARONproject.
This project was a collaboration
between STK and NT, represented by
NTR, Technical Department and Region
Oslo. One of the activity leaders was
Eliot Jensen, then at STK, who for me
became like a tutor in the teletraffic area.
The strange thing was that the very first
technical paper I was presented to by
Eliot in this project was, in fact, an article
by Palm: Calcul exact de la perte dans
les groupes de circuits échelonnés [1].
Here, Palm discusses the solution of a
simple grading with the help of state
equations. No closed form solution was
given by Palm, and I set out to solve the
problem by generating functions. It turned
out, though, that no general closed
form could be found by this technique,
either. Hence, I ended up solving the
whole thing numerically on a computer.
This possibility was definitely not easy at
hand in the thirties when Palm looked
upon the problem!
2 Conny Palm
Conny Palm was one of the most brilliant
scientists in the history of teletraffic
theory. Or perhaps I should say, in the
history of queuing theory, since Palm
really laid the mathematical fundamentals
of this theory. He was born in 1907,
joined the Royal Institute of Technology
in Stockholm in 1925, finished, in practice,
his studies in 1931 but did not take
his final exam in electrical engineering
until 1940. For nine years he was thus
what we would call an eternal student!
However, his nine extra student years
were by no means lazy years. From his
publication list we find seven papers
dated 1940 or earlier. From 1934 he
worked within the area of telephony and
joined Ericsson in 1936. He was an
active participant at Cramér’s seminars
on mathematical statistics at Stockholm’s
University where he in 1937 met William
Feller. This meeting turned out to be an
important one for further development of
the theory of stochastic processes; it was
a meeting between an academic scholar
searching for the fundamentals of probability
theory and a ‘practical’ engineer
who happened to have many of the
answers. Palm had obtained these
answers through his own work and the
work of his predecessors within telephony.
According to Cramér: “Palm presented
a unique, mature and clarified
view on his ideas of probability theory”.
And in fact, in 1950 Feller himself wrote:
“Waiting time and trunking problems for
telephone exchanges were studied long
before the theory of stochastic processes
was available and had a stimulating