1 - History of Ericsson - History of Ericsson

Fig. 2
Summation of deviations
"Opinion regions"
E = Excellent
G = Good
F = Fair
P = Poor
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From the point of view of the telephone public too great deviations mean
inconvenience and, in respect of public opinion, we can classify the calls as
• Excellent (E)
• Good (G)
• Fair (F)
• Poor (P)
• Bad (Bj
Every class can be given a maximum deviation value which can be illustrated
by vertical "opinion regions"-E, G, F, P and B-in our diagram. The more
equipment is involved in a call, the bigger the risk that the quality of the
call will fall in a lower class and the bigger the risk of unsatisfactory connexions.
From the diagram we can draw some general conclusions:
• When many parts are engaged on a call, unlucky combinations even of
small individual deviations can cause trouble, which cannot be traced
without overall testing of individual calls. There is always the risk that
serious faults in some parts, causing complaints, will be explained as
unlucky combinations and therefore not be traced by the maintenance
people.
• The greater the distance between the subscribers, the more equipment will
be engaged on a call and the bigger the risk of degraded quality.
• These calls will be the most expensive ones, and we can predict that the
public demands for performance especially during conversation will increase,
as poor intelligibility will prolong the conversation time and increase
the cost to the calling subscriber. In reality this means that the additional
equipment needed for long distance calls should be free from faults and
— 10
--50
.
— 90
—95
499a