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All drawings appearing in this Recommendation have been done in Autocad.
Recommendation E.420
CHECKING THE QUALITY OF THE INTERNATIONAL TELEPHONE SERVICE -
GENERAL CONSIDERATIONS
1 Quality of service parameters
An adequate picture of the level of quality of service (QOS) in the
network can be defined by a set of parameters which are measured, registered and
data processed.
In Recommendation E.800 a set of performance concepts is defined in order
to provide a satisfactory description of the quality of service, and the
interconnection of those concepts is shown. Each performance concept can be
impaired by a number of particular causes. These causes, either singly or in
groups, lie behind the failure symptoms observed by the user.
A user views the provided service from outside the network and his
perception can be described in observed quality of service parameters. The link
between the observed quality of service parameters and the impairment causes can
be indicated in the form of tables.1)
Five main observed quality of service parameters are derived; they reflect
the quality of:
i) providing the customer with the ability to use the desired services;
ii) furnishing a desired level of service for:
- connection establishment,
- connection retention,
- connection quality,
- billing integrity.
These main parameters can be supervised by quality of service indicators
(e.g. efficiency rate, call cut-off rate, etc.).
Objectives can be set for these indicators and can be revised at regular
intervals.
When a deterioration of these supervision indicators is detected, or when
an improvement programme is started, more data must be collected by measurements
to permit a more detailed analysis in order to locate the impairment causes which
lie behind the observed problem areas.
2 Methods of measuring the quality of service
2.1 The following methods of measuring the quality of service are described:
1) service observations by external means;
2) test call (simulated traffic);
3) customer interviews;
4) internal automatic observations.
2.2 Administrations are recommended to draw up a programme for observations
and tests designed for assessment of circuits and equipment, supervision of
operators and evaluation of the quality of service given to subscribers. It would
be desirable if telephone Administrations were to exchange statistics on quality
of service.
2.3 Table 1/E.422 relates to the manual and semi-automatic observations of the
quality of international automatic and/or semi-automatic service. It provides in
particular a check of the percentage of unsuccessful calls due to technical
faults (equipment shortages or failures).
Table 2/E.422 relates the same information as Table 1/E.422 but does not
include information which can only be obtained by operators listening in
(automatic observation).
Table 1/E.423 relates to observations on traffic set up by operators. It
provides, in manual and semi-automatic service, a means of determining the
efficiency of international circuits, of assessing the work of operators and the
quality of transmission.
Table 2/E.423 summarizes observations of the time-to-answer by operators.
The table is compiled by automatic means.
Table 1/E.424 is used to record the results of test calls undertaken
especially when the observations shown in Table 1/E.422 make it clear that the
percentage of faults is too high.
The use of customer interviews as a method of measuring telephone service
quality is the subject of Recommendation E.125 which is particularly concerned
with the determination of sources of user difficulty which may arise when making
an international automatic telephone call.
1) Such tables can be found in the handbook cited in [1].
Fascicle II.3 - Rec. E.420 PAGE1
Recommendation E.426 contains a general guide to the expected percentage
of effective international call attempts.
Table 1/E.427 may be used to supplement the information contained in Table
1/E.422 when the observations shown in that table make it clear that the
percentage of faults due to customer difficulties is too high or the outcome of
the application of Recommendation E.125 demonstrates the need for additional
information.
Recommendation E.425 describes the data that might be taken from the
switching centres with respect to quality of service, and the exchange of that
data.
2.4 Paying attention to the quality of service of the incoming traffic stream
is of major importance, since the incoming Administration is in a better position
to improve the situation.
In the past less attention has been paid by several Administrations to the
quality of service (QOS) on incoming calls than on outgoing calls. This situation
should not persist in the future.
Therefore, in addition to the measurement of QOS of the outgoing traffic
stream which is described in this series of Recommendations, Administrations are
strongly advised to observe the incoming traffic stream with the aim to improve
the QOS.
3 Other sources of information on the quality of service
The following sources are useful to consider when trying to improve the
quality of service:
- subscriber complaints (see Annex B);
- other Administrations or organizations such as INTELSAT (SPADE
reports);
- operators contacting maintenance staff for direct action;
- operators giving information on QOS: if operator traffic is significant
one might consider organizing the flow of this type of information by
establishing "trouble codes", e.g. echo, no tone, no answer, etc.;
- reports from "national" switching centres: the QOS as experienced by
the subscriber does not only depend on the international network and
the network of the country of destination but also on the national
network of the country of origin;
- user organizations/large companies: as large companies have much to
gain from an improved QOS they might be willing to cooperate with
Administrations;
- holding time versus conversation time measurements;
- average conversation time;
- traffic measurements;
- transmission measurements.
PAGE2 Fascicle II.3 - Rec. E.420
ANNEX A
(to Recommendation E.420)
A possible approach to integrate activities measuring
the quality of service into an overall problem-investigating process
The flowcharts of the resource allocation process and a typical problem
identification procedure are given in Figures A-1/E.420 and A-2/E.420. The
numbers 1) through 10) in the figures correspond to the processes described
below.
1) The exception threshold is set to detect possible isolated
destinations. It is up to the individual Administration to set the
value.
2) A destination could be regarded as being under isolated condition when
the bid frequency is significant enough to show that there is some
demand to the destination (e.g. 20 attempts per day) without or nearly
without answer.
3) The most practical way to find out whether improvements may be possible
is "consultation with other Administrations".
4) Apply, if possible, network management actions, e.g. alternative
routing.
5) The destination priority, P, for each destination is calculated as
follows:
P = BID2) x (TABR - MABR)
where
BID2) is the number of total bids to the destination during a certain
period of time (for example, 1 month);
TABR is the target ABR3) (answer bid ratio) performance which is
expected as the result of the service improvement activities;
MABR is the measured ABR to the destination during the same period with
BID.
The TABR is set for each destination and can be based on the average
historic ABR and should be higher than that value.
In order to comply with Recommendation E.426, S 2.2, the TABR to be
used in the formula for P given above should not be lower than the MABR
experienced one period earlier.
6) In order to comply with S 2.4, it is suggested to consider also the
total international incoming traffic stream as one of the elements
which require QOS improvements. It should be noted that the procedure
can be well applied to domestic destinations, for example, on an area
code basis, and can be applied on an incoming route basis.
7) Perform detailed analysis: when possible, monitor circuit group
performance and do analyses on a destination code basis. It is
essential to be aware of "killer trunks" (though observation of the QOS
is not directly intended to discover killer trunks).
8) Discuss possible improvements with counterpart.
9) In Recommendation M.710 (General maintenance organization for the
international automatic and semi-automatic service) the basic
maintenance elements, their functions and the cooperation between the
elements are described. Recommendation M.1230 (Assessment of the
performance of the international telephone network) gives guidance on
the relationship between service quality observations, network
performance assessment and maintenance procedures. It should be noted
that the QOS very much depends on the proper operation of maintenance
elements and maintenance procedures. Therefore, Administrations faced
with QOS problems are strongly advised to be attentive to the
maintenance Recommendations contained in Volume IV.
10) If this procedure does not lead to a successful conclusion, then an
escalation procedure may be required (see Recommendation M.711).
2) Paid minutes or the revenues can be used.
3) In case ABR cannot be used, ASR (answer seizure ratio) is considered to be an
acceptable substitute. Seizures, TASR and MASR are then applicable.
Fascicle II.3 - Rec. E.420 PAGE1
Figure A-1/E.420 - T0201270-88
Figure A-2/E.420 - T0201280-88
ANNEX B
(to Recommendation E.420)
Utilization of customer complaints to improve the quality of
service for international traffic
It is possible to use subscriber complaints to control processes if the
organization of an Administration provides possibilities for centralized
collection of these complaints.
The collected data can be processed statistically to provide useful
indications for the operations and maintenance staff to correct problems and, in
so doing, improve the quality of service.
Three aspects are relevant in the processing of the data:
- the data itself;
- the statistical processes;
- the analysis of complaints.
B.1 Data to be collected
The trouble report of an individual customer may be subjective and
unqualified since it is usually made by a person, who is not well trained for
observation of quality of service. Therefore it will be necessary to make sure
that the information about the complaint is as reliable as possible and useful
for identifying the possible impairment of the network that caused the complaint.
Examples (see also the handbook cited in [1]):
- data concerning the subscriber numbers involved (route, destination);
- data concerning the observations during the unsuccessful call
attempt(s), or the disturbed call;
- time of the observation by the customer.
B.2 Statistical processes to improve the reliability of the data
Reliable data is obtained by statistical processing of large numbers of
complaints (e.g. an average value during a certain period of time). In order to
achieve this, the following methods are considered to be useful:
1) choose complaints whose possible causes seem to relate to impairments
of the network;
2) accumulate complaints for a certain period of time, for example, one
month or one week, depending on the number of complaints;
3) calculate the ratio of complaints statistically from accumulated data,
for example, complaint-to-completion ratio (CTCR), for the chosen
period of time:
CTCR = eq \f( Number of complaints, Number of effective call
attempts) x 100%
It is practical to use the CTCR in combination with one or more
classification aspects (see S B.3) such as "per destination".
B.3 Analysis of complaints
It is necessary to identify the possible impairment of the network causing
the complaint and smoothly clear this impairment in order to actually improve the
quality of service. To accomplish this, the complaint needs to be processed into
data useful to network maintenance organizations in localizing the possible
impairment. The following methods are considered useful:
1) classifying complaints by category of failure;
2) classifying complaints by destination, route (or circuit group) and/or
area code;
3) time of day analysis. This may be effective in identifying impairments
that may not be apparent when looked at on a total day basis;
4) highlighting relative changes or trends in the statistical data. These
changes are likely to reflect a change of the network status and are
useful indications along with the values themselves. For example, a
rapid increase in the statistical value (e.g. the ratio of complaints)
may reflect a new impairment of the network.
Reference
[1] CCITT Manual Quality of service, network management and network
maintenance, ITU, Geneva, 1984.
PAGE2 Fascicle II.3 - Rec. E.420
