dr.-ing. h. w. gierlich head of telecom division

Colombia, 23-24 September 2013

The importance of models and procedures The importance of models and procedures for planning, monitoring and control in the for planning, monitoring and control in the

provision of communications servicesprovision of communications servicesDr.-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

Outline

IntroductionCommunication Services – Underlying System configurations Planning: The ITU-T E-model (G.107 & G.108)Network Monitoring: P.862, P.863 & P.563Wideband – The new ChallengeSummary

ITU-T: QoS and QoEQuality 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

Speech Quality – what we would like to have


1m

““orthotelefonic reference position”orthotelefonic reference position”

Speech Quality…


speechquality

talkingsituation

listeningsituation

conversationalsituation

… from the user’s perspective

End to End Conifguration


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 !add. 1 - 100 ms !

Netw. 2

Impact on speech quality: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 :

delaydelay – unpredictable, load dependant, time variant

Contributions to Quality

The networksType of networksInterconnectionQoS management

The endpointsTypes of terminalsInteroperability

Terminal – NetworkTerminal – Terminal

The users‘ locationEnvironmental conditions


• Network planningNetwork planning

• Network monitoringNetwork monitoring

• Laboratory Laboratory terminal testingterminal testing

• Interoperability Interoperability testing testing


8

Outline


Reference Connection in the E-model


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)


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 Impairment factorsfactors

Simultaneous impairment factor Is Is (non optimum loudness rating, non optimum sidetone, PCM coding distortion)

Delayed impairment factor Id Id (impact of delay, talker- or listener echo)

Equipment impairment factor Ie Ie (all types of impairments in equipment such as coding distortion including the effect of packet loss)


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.113From subjective listening tests described in ITU-T P.833From objective models (e.g. ITU-T P.863) following the procedure in ITU-T P. 834


Some Ie factors from G.113


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:


1000 R

1MOSCQE

6CQE 107)100)(60(035.01MOS RRRR

5.4MOSCQE

Guide for User Satisfaction based on R-values


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



17

Outline


Networks & Network Monitoring

Main network related impairments:DelayDelay variation (jitter)Listening speech impairment due to

CodingTranscodingInterconnection Packet loss/jitter


ITU-T Models for Perceptual based Speech Quality Measurement

ITU-T P.862 (2001): PESQITU-T P.863 (2011): POLQAThe basic principle:


PrincipleIntrusive test procedureObjective prediction of MOS (mean opinion score) as achieved in listening test subjectively Prediction on a MOS-scale:

MOS 5 – excellentMOS 4 – goodMOS 3 – fairMOS 2 – poorMOS 1 – bad

Substitution of subjective tests for known codecs and impairments


Application

Intrusive testing:Insertion of a reference speech sequenceAcquiring the transmitted, distorted speech sequenceCalculation of the speech quality by comparing to the referenceOutput: MOS LQOn – MOS LQOn – mean opinion score, objective, narrowband


Typical setups


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 sequences

FixedNetwork 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 callNo reference file insertion requiredAverage listening speech quality prediction on statistical evaluation of a high number of calls on the same connectionNot recommended for test on a call by call basisMuch less reliable than intrusive testing based on P.862 and P.863


The wideband challenge

High quality expectation by the userWideband must be significantly better in all quality aspectsSignificant contribution to quality by the terminalsFirst attemt to certify high quality wideband speech transmission: GSMA


Wideband listening examples


(.wav)

FullbandNarrowband

Wideband

Mobile Phone

Mobile signal

processingRF-Interface

air interface

SpeechTranscoder

speechspeechnoisenoise

Wideband (.wav)

Narrowband (.wav)……in noisein noise

Wideband Network Planning – ITU-T G.107.1

The principle of the model is identical to the narrowband version G.107The 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 0-100All factors – R0 and Impairment factors are adapted accordingly


Wideband Network Monitoring

Setup as in narrowbandOnly intrusive testing available Network monitoring is based on ITU-T P.863 POLQAITU-T P.862 PESQ should not be used in wideband


Conclusions and Recommendations

ITU-T provides models for planning and monitoringNetwork planning is essential for achieving high network QoSNetwork 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


28

dr.-ing. h. w. gierlich head of telecom division

Documents

itut emodel

equipment impairment

new challengesummaryitut

emodelrating factor

system configurations

psychological factors

analog network components

quality of experience