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)
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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
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.
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Speech Quality –what we would like to have
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1m
“orthotelefonic reference position”
Speech Quality…
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speechquality
talkingsituation
listeningsituation
conversationalsituation
… from the user’s perspective
End to End Conifguration
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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
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
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• Network planning
• Network monitoring
• Laboratory terminal testing
• Interoperabilitytesting
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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
Reference Connection in the E-model
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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)
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AIe-effIdIsRoR +−−−=
Basic assumption: Psychological factors on the psychological scale are additive
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
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Codec type ReferenceOperating
rate[kbit/s]
Ievalue
PCM (see Note) G.711 64 0ADPCM G.726, G.727 40 2
G.721, G.726, G.727 32 7G.726, G.727 24 25G.726, G.727 16 50
LD-CELP G.728 16 712.8 20
CS-ACELP G.729 8 10G.729-A + VAD 8 11
RPE-LTP GSM 06.10, full-rate 13 20VSELP GSM 06.20, half-rate 5.6 23ACELP GSM 06.60,
enhanced full rate12.2 5
ACELP G.723.1 5.3 19MP-MLQ G.723.1 6.3 15
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:
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1000 <<R
1MOSCQE =
6CQE 107)100)(60(035.01MOS −⋅−−++= RRRR
5.4MOSCQE
=
Guide for User Satisfaction based on R-values
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Range of E-Model Rating R
Speech transmission
quality category
User satisfaction
90 ≤ R < 100 Best Very satisfied80 ≤ R < 90 High Satisfied70 ≤ R < 80 Medium Some users
dissatisfied60 ≤ R < 70 Low Many users
dissatisfied50 ≤ R < 60 Poor Nearly all users
dissatisfiedConnections with E-Model Ratings R below 50 are not recommended.
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
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:
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Typical Processing Steps (Schematic):
Adaptation Hearing Model
Comparison,Reference,Reduction,Signal Value
Results ofListening Tests!
S indexQ
Speech Signal
Test Object Hearing Modelprocessed
signal
reference signal
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
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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
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Central server- automated call setup- generation of test
sequences- analysis & statistics
FixedNetwork
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 sequencesFixed
Network 2
Very difficult in monitoring: network one way transmission
delay
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
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(.wav)
Fullband
Narrowband
Wideband
Mobile Phone
Mobile signal
processingRF-Interface
air interface
SpeechTranscoder
speech
noise
Wideband (.wav)
Narrowband (.wav)…in noise
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 ITU-T 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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