Contents Telektronikk - Telenor

Analysis of external traffic at UNIT/SINTEF’s
MD110 telephone exchange
BY BONING FENG AND ARNE MYSKJA
1 Introduction
Since the 1950s three generations of
automatic telephone exchanges have
been installed at the University of Trondheim
(UNIT):
1 A main exchange of type AGF (delivered
by Ericsson), electromechanical
type, together with 17 smaller
exchanges geographically distributed
both in and outside the main campus
area. The exchanges covered UNIT
and the research institute SINTEF, and
was in service until May 1977.
2 A Metaconta 10R exchange (delivered
by LMT Paris), a computerised system
with mechanical contacts. It covered
UNIT and SINTEF except some
remote units. From 1982 the Regional
Hospital of Trondheim (RiT) was also
connected to the same exchange. This
exchange was in service from May
1977 to January 1990.
3 In January 1990 a new telephone
exchange, MD110 (delivered by Ericsson)
was installed at UNIT/SINTEF.
The exchange is fully electronic, digital,
and distributed. It consists of 36
switching units (LIMs) on 16 different
sites which are connected by a star network
with altogether 54 internal
2 Mb/s leased circuits. The new
exchange covers all the units of UNIT
and SINTEF, but not RiT.
This paper presents some results from the
traffic analysis at the new exchange. Due
to the limitations of the registration functions
implemented in the MD110 it is not
possible to make detailed studies of the
incoming traffic. Another type of registration
mechanism which MD110 lacks,
is the possibility to register the distribution
of the internal traffic. Therefore our
study is focused on direction-based analysis
of outgoing external traffic at the
telephone exchange. The results presented
here cover
- number of calls
- traffic volume, and
- duration of calls.
The study includes traffic profiles of 24
hour and full week periods, and how they
are distributed among the different service
types and charging groups. We also
look at the number of calls and the traffic
to the other universities in Norway. The
number of incoming call attempts was
also registered in order to get an indication
of the relation between incoming
and outgoing calls.
In addition to averages, distributions are
also included. Histograms are given for
some distributions. In most cases mean,
standard deviation and coefficient of
variation are calculated.
2 Traffic observations
2.1 Overview of the telephone
exchange at UNIT/SINTEF
At the time of observation the system
consisted of the following parts:
- 36 LIMs
- 54 leased circuits, each with thirty
64 kb/s channels
- 2 group selectors in load-sharing mode
- 7 two-way ISDN primary access with
a total of 210 channels
- 2 outgoing PCM groups with a total of
60 channels
- 40 outgoing analogue reserve lines
- 6500 extensions.
2.2 The data registration
system
Traffic observations have been undertaken
on all three generations of telephone
exchanges:
- on AGF exchange by analysis of the
charging data stored on magnetic
tapes, collected by a charging system
developed by NTH (The Norwegian
Institute of Technology) [1]
- on Metaconta 10R by analysis of the
automatic registrations made by the
system, and by corresponding analysis
of the charging data [2, 3, 4]
- on MD110 by data registered by the
supporting system TELMAX, and by
analysis of the charging data [6].
Despite the limitations mentioned above,
the traffic registration in MD110 is still
quite extensive, and they are made available
through the supporting system TEL-
MAX. Combined with the charging data
generated by TELMAX, the data sets for
the following types of analysis are available:
- number of call attempts, traffic intensity
and volume at all server groups,
internal and external trunk groups
- number and holding times of calls,
traffic intensity and volume, distributed
on arbitrary external traffic directions,
defined by the numbers called
(direction-based analysis).
The direction-based analysis is based on
the charging data. In order to secure the
privacy of the employees, all the calling
numbers have been deleted during our
analysis. Neither is any analysis based on
particular numbers.
The supporting system TELMAX is also
distributed, using the broadband network
already installed in UNIT/SINTEF and
local Ethernet-segments. The system is
PC-based (at UNIT/SINTEF IBM PS2
are used). There are altogether 21 PCs in
the TELMAX system.
The traffic module in TELMAX generates
directly graphical curves showing the
number of call attempts and the traffic.
The output data are averages, i.e. measurements
of load on server groups like
leased circuits, signalling equipment, etc.
For incoming traffic there is no direct
registration mechanism. However, it is
possible to measure
- number of call attempts
- number of calls which are set up manually
(through the exchange switchboard)
- total traffic (sum of incoming- and outgoing
traffic).
These registrations are not done automatically;
they must be initiated manually.
The information of outgoing calls are
given by the charging data, which supply
detailed information of every single successful
call, including B-numbers. A typical
record in a charging file is shown in
Figure 1. It is possible to make analysis
as detailed as desired. This kind of analysis
has been performed earlier for the
purpose of studying the statistics for
repeated calls [1]. In the present study all
the A-numbers have been deleted, so the
direction-based analysis gives collective
results for the whole exchange.
2.3 Arrangement of the
observations
2.3.1 The observation periods
The charging files from two observation
periods in the 4th quarter of 1991 have
been collected:
- Period 1: Monday 1991.10.07 –
Sunday 1991.10.20
- Period 2: Monday 1991.11.25 –
Sunday 1991.12.08
Both periods have a two week duration.
Since October is considered a “normal
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