Consultation Paper on Quality of Service (QoS) - ICTA

End-to- End
Transmission Time
Limits
0 to 150 ms
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Table A13: End-to-end transmission time limits
Acceptable for most user
applications
Note
Some highly interactive voice and data
applications may experience degradation for
values below 150 ms. Therefore, increases in
processing delay on connections with
transmission times even well below 150 ms
should be discouraged unless there are clear
service and application benefits.
150 to 400ms Acceptable provided that
Administrations are aware of
the transmission time impact
on the transmission quality of
user applications.
Above 400 ms Unacceptable for general
network planning purposes;
however, it is recognized that
in some exceptional cases this
limit will be exceeded.
For example, international connections with
satellite hops that have transmission times
below 400 ms are considered acceptable.
Examples of such exceptions are
unavoidable double satellite hops, satellites
used to restore terrestrial routes, fixed
satellite and digital cellular interconnections,
videotelephony over satellite circuits, and
very long international connections with two
digital cellular systems connected by long
terrestrial facilities.
Transmission delay is a very important parameter for any application whose overall performance is
dependent on user or terminal interactivity. Applications such as voice, voiceband data, digital data,
and videotelephony may involve user tasks or terminal equipment characteristics that vary
substantially in their sensitivity to transmission delay.
A.5.2 E-Model
For transmission planning purposes, the E-model is a useful tool for assessing the combined effect
of all of the abovementioned parameters, including transmission delay. ITU-T Recommendations
G.108 and G.175 provide detailed guidance for transmission planning using the E-model. The
primary output of the E-model is the Transmission Rating Factor R. The following table from ITU-
T Recommendation G.109 provides the definition of different categories of speech transmission
quality in terms of the Transmission Rating Factor R. The results can be converted into numbers on
the MOS scale in ways that can predict to some extent the MOS for conversation.
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Table A14: Categories of speech transmission quality
Speech transmission
R-value range
User satisfaction
quality category
90 R < 100
80 R < 90
70 R < 80
60 R < 70
Best
High
Medium
Low
Very satisfied
Satisfied
Some users dissatisfied
Many users dissatisfied
34 ITU-T Recommendation G.114
35 Source : ITU-T Recommendation G.109
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