CITEL (PCC.I)/ ITU Forum on Information and
Communication Technology Service:
Quality, Control and Surveillance
(Cartagena de Indias, Colombia, 23-24 September 2013)
The importance of models and procedures
for planning, monitoring and control in the
provision of communications services
Dr.-Ing. H. W. Gierlich
Head of Telecom Division
Colombia, 23-24 September 2013
Outline
Introduction
Communication Services –
Underlying System configurations
Planning: The ITU-T E-model (G.107
& G.108)
Network Monitoring: P.862, P.863 &
P.563
Wideband – The new Challenge
Summary
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ITU-T: QoS and QoE
Quality of Service (QoS):
Totality of characteristics of a
telecommunications service that bear on its
ability to satisfy stated and implied needs of
the user of the service.
Quality of Experience (QoE):
The overall acceptability of an application or
service, as perceived subjectively by the enduser.
Quality of experience includes the complete end-to-end system effects (client,
terminal, network, services infrastructure, etc.).
Overall acceptability may be influenced by user expectations and context.
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Speech Quality –
what we would like to have
1m
“orthotelefonic reference position”
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Speech Quality…
… from the user’s
perspective
talking
situation
speech
quality
listening
situation
conversational
situation
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End to End Conifguration
add. 1 - 100 ms !
DSL
IPGW
Netw. 1
10 - 400 ms
IPGW
ISC
ISC
GW
MSC
BSS
PSTN
Netw. 2
10 - 400 ms
PBX
240 ms
1-15 ms
90-120 ms
Impact on speech quality:
-
A big problem of today‘s networks,
interconnection & terminals :
delay – unpredictable, load
dependant, time variant
delay now time variant
echo much more dominant
Coding distortion
background noise problems
insufficient quality of the analog network components (att., noise, distortion…)
insufficient quality of acoustical components
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Contributions to Quality
The networks
Type of networks
Interconnection
QoS management
• Network planning
• Network monitoring
The endpoints
Types of terminals
Interoperability
Terminal – Network
Terminal – Terminal
• Laboratory
terminal testing
• Interoperability
testing
The users‘ location
Environmental conditions
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Outline
Introduction
Communication Services –
Underlying System configurations
Planning: The ITU-T E-model (G.107
& G.108)
Network Monitoring: P.862, P.863 &
P.563
Wideband – The new Challenge
Summary
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Reference Connection in the E-model
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Transmission Rating in the E-model
Rating factor R:
R  Ro  Is  Id  Ie-eff  A
With:
R0 – Basic signal to noise ratio
(takes into
account circuit noise, room noises)
Ix – Impairment factors (see next slide)
A – Advantage factor (takes into account a
potential advantage for a user for a specific transmission
in a specific situation)
Basic assumption:
Psychological factors on the psychological scale are additive
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Network planning & E-model (ITU-T
G.107 & G.108)
Basis of the E-model: Impairment
factors
Simultaneous impairment factor Is
(non
optimum loudness rating, non optimum sidetone, PCM
coding distortion)
Delayed impairment factor Id
(impact of
delay, talker- or listener echo)
Equipment impairment factor Ie
(all types
of impairments in equipment such as coding distortion
including the effect of packet loss)
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How to derive Ie?
Ie is based on subjective tests and
can be derived as follows:
Equipment impairment factors for the
most popular codecs in ITU-T G.113
From subjective listening tests
described in ITU-T P.833
From objective models (e.g. ITU-T
P.863) following the procedure in ITU-T
P. 834
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Some Ie factors from G.113
Codec type
PCM (see Note)
ADPCM
LD-CELP
CS-ACELP
RPE-LTP
VSELP
ACELP
ACELP
MP-MLQ
Reference
G.711
G.726, G.727
G.721, G.726, G.727
G.726, G.727
G.726, G.727
G.728
G.729
G.729-A + VAD
GSM 06.10, full-rate
GSM 06.20, half-rate
GSM 06.60,
enhanced full rate
G.723.1
G.723.1
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Operating
rate
[kbit/s]
64
40
32
24
16
16
12.8
8
8
13
5.6
12.2
5.3
6.3
Ie
value
0
2
7
25
50
7
20
10
11
20
23
5
19
15
13
The E-model Prediction Range
R – value range: prediction on a
scale
0R 100
Mapping to MOS:
For R  0:
MOSCQE 1
For 0  R  100:
MOSCQE 1 0.035R  R(R  60)(100  R)7106
For R  100:
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MOSCQE  4.5
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Guide for User Satisfaction
based on R-values
Range of E-Model
Rating R
90  R  100
80  R  90
70  R  80
60  R  70
50  R  60
Speech
transmission
User satisfaction
quality
category
Best
Very satisfied
High
Satisfied
Medium
Some users
dissatisfied
Low
Many users
dissatisfied
Poor
Nearly all users
dissatisfied
Connections with E-Model Ratings R below 50 are not recommended.
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Guide on Transmission Planning:
ITU-T G.108
Demonstrates the application of the
E-model for end-to-end transmission
planning in a wide range of networks
Keep in mind: G.107 and G.108 are
applicable for narrowband networks
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Outline
Introduction
Communication Services –
Underlying System configurations
Planning: The ITU-T E-model (G.107
& G.108)
Network Monitoring: P.862, P.863 &
P.563
Wideband – The new Challenge
Summary
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Networks & Network Monitoring
Main network related impairments:
Delay
Delay variation (jitter)
Listening speech impairment due to
Coding
Transcoding
Interconnection
Packet loss/jitter
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ITU-T Models for Perceptual based
Speech Quality Measurement
ITU-T P.862 (2001): PESQ
ITU-T P.863 (2011): POLQA
The basic principle:
Typical Processing Steps (Schematic):
Speech
Signal
Test Object
Adaptation
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processed
signal
reference
signal
Hearing Model
Hearing Model
Results of
Listening Tests!
Comparison,
Reference,
Reduction,
Signal Value
SQindex
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Principle
Intrusive test procedure
Objective prediction of MOS (mean
opinion score) as achieved in listening
test subjectively
Prediction on a MOS-scale:
MOS
MOS
MOS
MOS
MOS
5
4
3
2
1
–
–
–
–
–
excellent
good
fair
poor
bad
Substitution of subjective tests for known
codecs and impairments
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Application
Intrusive testing:
Insertion of a reference speech
sequence
Acquiring the transmitted, distorted
speech sequence
Calculation of the speech quality by
comparing to the reference
Output: MOS LQOn – mean opinion
score, objective, narrowband
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Typical setups
Mobile
Network
Central server
- automated call setup
-generation of test
sequences
- analysis & statistics
Mobile Probe
- automated call
setup
-generation of
test sequences
Mobile Probe
- automated call
setup
-generation of
test sequences
Fixed
Network
Fixed
Network 2
Very difficult in monitoring:
network one way transmission
delay
Probe @ NTP
- automated call
setup
-generation of
test sequences
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Probe @ NTP
- automated call
setup
-generation of
test sequences
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Not Intrusive Testing - ITU-T P.563
Listening speech quality prediction based
on speech signal in a call
No reference file insertion required
Average listening speech quality prediction
on statistical evaluation of a high number
of calls on the same connection
Not recommended for test on a call by
call basis
Much less reliable than intrusive testing
based on P.862 and P.863
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The wideband challenge
High quality expectation by the user
Wideband must be significantly
better in all quality aspects
Significant contribution to quality by
the terminals
First attemt to certify high quality
wideband speech transmission:
GSMA
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Wideband listening examples
Fullband
Narrowband
Wideband
Narrowband
Wideband
…in noise
noise
speech
Mobile
signal
processing
Speech
Transcoder
air interface
RF-Interface
Mobile Phone
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Wideband Network Planning –
ITU-T G.107.1
The principle of the model is identical to
the narrowband version G.107
The model reflects the improvements in
quality in wideband:
Maximum R = 129 (instead of 100 for
narrowband)
Model provides new wideband R calculation
mapping R to the range of 0-100
All factors – R0 and Impairment factors are
adapted accordingly
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Wideband Network Monitoring
Setup as in narrowband
Only intrusive testing available
Network monitoring is based on ITUT P.863 POLQA
ITU-T P.862 PESQ should not be
used in wideband
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Conclusions and Recommendations
ITU-T provides models for planning and
monitoring
Network planning is essential for achieving
high network QoS
Network monitoring is essential to detect
potential issues – e.g. changing radio
conditions, changing network conditions
(jitter, packet loss)
Both is not sufficient to guarantee a good
QoE – terminals play a major role for the
overall speech quality
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