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La importancia de los modelos y procedimientos para la planificación, seguimiento y control en la prestación de servicios de comunicación
1. 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
CITEL (PCC.I)/ ITU Forum on Information and
Communication Technology Service:
Quality, Control and Surveillance
(Cartagena de Indias, Colombia, 23-24 September 2013)
2. Colombia, 23-24 September 2013 2
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
3. 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 end-
user.
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.
Colombia, 23-24 September 2013 3
4. Speech Quality –
what we would like to have
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1m
“orthotelefonic reference position”
5. Speech Quality…
Colombia, 23-24 September 2013 5
speech
quality
talking
situation
listening
situation
conversational
situation
… from the user’s
perspective
6. End to End Conifguration
Colombia, 23-24 September 2013 6
ISCDSL ISC PBX GW
PSTN
1-15 ms240 ms
MSC BSS
90-120 ms
IP-
GW
Netw. 1
IP-
GW
10 - 400 ms10 - 400 ms
add. 1 - 100 ms !
Netw. 2
Impact on speech quality:
- 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
A big problem of today‘s networks,
interconnection & terminals :
delay – unpredictable, load
dependant, time variant
7. Contributions to Quality
The networks
Type of networks
Interconnection
QoS management
The endpoints
Types of terminals
Interoperability
Terminal – Network
Terminal – Terminal
The users‘ location
Environmental conditions
Colombia, 23-24 September 2013 7
• Network planning
• Network monitoring
• Laboratory
terminal testing
• Interoperability
testing
8. Colombia, 23-24 September 2013 8
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
10. Transmission Rating in the E-model
Rating factor R:
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)
Colombia, 23-24 September 2013 10
AIe-effIdIsRoR +−−−=
Basic assumption:
Psychological factors on the psychological scale are additive
11. 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)
Colombia, 23-24 September 2013 11
12. 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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14. The E-model Prediction Range
R – value range: prediction on a
scale
Mapping to MOS:
For R < 0:
For 0 < R < 100:
For R > 100:
Colombia, 23-24 September 2013 14
1000 <<R
1MOSCQE
=
6
CQE
107)100)(60(035.01MOS −⋅−−++= RRRR
5.4MOSCQE
=
15. Guide for User Satisfaction
based on R-values
Colombia, 23-24 September 2013 15
Range of E-Model
Rating R
Speech
transmission
quality
category
User satisfaction
90 ≤ R < 100 Best Very satisfied
80 ≤ R < 90 High Satisfied
70 ≤ R < 80 Medium Some users
dissatisfied
60 ≤ R < 70 Low Many users
dissatisfied
50 ≤ R < 60 Poor Nearly all users
dissatisfied
Connections with E-Model Ratings R below 50 are not recommended.
16. 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
Colombia, 23-24 September 2013 16
17. Colombia, 23-24 September 2013 17
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
18. Networks & Network Monitoring
Main network related impairments:
Delay
Delay variation (jitter)
Listening speech impairment due to
Coding
Transcoding
Interconnection
Packet loss/jitter
Colombia, 23-24 September 2013 18
19. ITU-T Models for Perceptual based
Speech Quality Measurement
ITU-T P.862 (2001): PESQ
ITU-T P.863 (2011): POLQA
The basic principle:
Colombia, 23-24 September 2013 19
Typical Processing Steps (Schematic):
Adaptation Hearing Model
Comparison,
Reference,
Reduction,
Signal Value
Results of
Listening Tests!
S indexQ
Speech
Signal
Test Object Hearing Model
processed
signal
reference
signal
20. Principle
Intrusive test procedure
Objective prediction of MOS (mean
opinion score) as achieved in listening
test subjectively
Prediction on a MOS-scale:
MOS 5 – excellent
MOS 4 – good
MOS 3 – fair
MOS 2 – poor
MOS 1 – bad
Substitution of subjective tests for known
codecs and impairments
Colombia, 23-24 September 2013 20
21. 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
Colombia, 23-24 September 2013 21
22. Typical setups
Colombia, 23-24 September 2013 22
Central server
- automated call setup
- generation of test
sequences
- analysis & statistics
Fixed
Network
Probe @ NTP
- automated call
setup
- generation of
test sequences
Probe @ NTP
- automated call
setup
- generation of
test sequences
Mobile
Network
Mobile Probe
- automated call
setup
- generation of
test sequences
Mobile Probe
- automated call
setup
- generation of
test sequences
Fixed
Network 2
Very difficult in monitoring:
network one way transmission
delay
23. 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
Colombia, 23-24 September 2013 23
24. 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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25. Wideband listening examples
Colombia, 23-24 September 2013 25
(.wav)
Fullband
Narrowband
Wideband
Mobile Phone
Mobile
signal
processing
RF-Interface
air interface
Speech
Transcoder
speech
noise
Wideband
(.wav)
Narrowband
(.wav)
…in noise
26. 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
Colombia, 23-24 September 2013 26
27. Wideband Network Monitoring
Setup as in narrowband
Only intrusive testing available
Network monitoring is based on ITU-
T P.863 POLQA
ITU-T P.862 PESQ should not be
used in wideband
Colombia, 23-24 September 2013 27
28. 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
Colombia, 23-24 September 2013 28