A path towards common quality assessment of narrowband and wideband voice

Trond Ulseth, Telenor R&D(trond.ulseth@telenor.com)

Workshop on Wideband Speech Quality in Terminals and Networks: Assessment and Prediction

8th and 9th June 2004 - Mainz, Germany

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Outline

The history of wideband, Why has wideband not been a success (on ISDN)? A new era for wideband, What we (the telcos) can offer and what our customers

need, The answer, A proposal for development of an extended (all-purpose) E-

model.

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The history of wideband

1988: CCITT published recommendation G.722, 1989/90: EuroISDN MoU signed, 1990: ISDN Test services in Europe, Tandberg Telecom launched an ISDN videophone at

Telecom91 in Geneva. The videophone supported both narrowband and wideband audio,

1994: Videophones (and wideband telephony) was used to e.g. when interviewing athletes staying at the Olympic village at the Olympic Winter Games, Lillehammer, Norway,

1994: ISDN 7 kHz telephony teleservice defined by ETSI, 1999: ITU-T Recommendation G.722.1 published, 2002: First version of ITU-T Recommendation G.722.2

(AMR-WB) published.

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The (missing) success of wideband telephony on the ISDN Wideband telephony on the ISDN (the telephony 7 kHz

teleservice) has not been a success, Wideband voice for videotelephony/videoconferencing has

been a success, Narrowband telephony vs.

Wideband telephony on the ISDN –Is it the chicken and egg problem?

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Telecom Innovators NewsMay 2004

HiFi VoIP — Better than PSTN Voice

                       

  By R. Brough Turner, SVP & CTO, NMS

VoIP has been available in various forms since 1995–96, but significant adoption is a fairly recent phenomenon. The most often cited reason for this long incubation period is voice quality. Even today, IT directors worry that IP-PBX voice quality may not match expectations. This is unfortunate as VoIP has the potential to offer much better voice quality than the PSTN!Luckily, examples of HiFi VoIP are appearing in the market with additional products in the pipeline. Over the next two years we’ll see increasing recognition of how HiFi VoIP overcomes the quality problems of PSTN telephony.

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VoIP/MMoIP – a new era for wideband telephony? Most users don’t care about the technology, they care about

the quality/performance, VoIP has some similarities with the voice application of the

videotelephoney and videoconferencing services; there is not a separate service but the users can choose the coding algorithm (and quality),

Global IP Sound has a wideband codec that is robust against packet loss. Products where this codec is implemented are available,

Microsoft has included the Siren codec in Windows XP/ Windows Messenger.(Siren is the 16 kbit/s mode of the G.722.1 codec).

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VoIP/MMoIP – a new era for wideband telephony?(more)

The ITU-T Recommendation G.772.2 codec is standardised by 3GPP as the AMR-WB codec,

Press reviews have emphasised the improved quality of some products (e.g. Skype),

Conclusion:Wideband telephony will probably be a success, particularly for non-handset applications (headset and hands-free)

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IP Networks – Diverse quality

Traditional IP networks are Best effort networks, To meet the requirements of real-time communication there has

been a lot of work on implementing QoS mechanisms in IP networks,

IP Network QoS classes are defined in ITU-T Recommendation Y.1541,

A network QoS class definition is not sufficient for the user,– Networks not belonging to the operator domain such as WLAN are not

included,– Media processing (voice coding) and other terminal related characteristics are

not included. ETSI User Group recommends that there should be a

standardized way to determine and present quality of service, system reliability and durability. This should include the development of standardized performance indicators.

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Real-time service classes in an IP environment The network performance depends on factors such as

network architecture, technology used and traffic, ITU-T Recommendation Y.1541 defines two real-time

communication service QoS classes where the degree of interaction defines the delay requirement,

ETSI TS 101 329-2 defines three speech QoS classes. However, the middle class (Narrowband) is divided into three sub-classes.The highest and lowest classes are

– Wideband (highest),– Best effort (lowest).

3GPP TS 23.107 defines four QoS classes, one is the conversational class.

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Our customers need a simple user perception based classification The majority of our customers will not be able to assess the added effects

of a number of parameters such as,– Delay,– Jitter,– Packet loss,– Dynamic range,– Media bandwidth, – Echo suppression,–

To define a single QoS class for e.g. voice tells the user that there is some mechanism in the network, but gives no information about the performance or a possibility to choose the desired performance.

Conclusion: We need an Index that is easy to understand. Telenor has been working on a Product Performance Index to describe the user perceived quality for different transmission technologies with a focus on data communication.A similar approach should be used for voice.

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How to compare narrowband voice and wideband voice? Subjective testing is of course the basis, However, there is a need for a tool based on objective

measurements, The ultimate goal should be a calculation model where the

performance of both narrowband voice and wideband voice could be estimated,

A possible approach that has already been used by service providers and standardisation bodies is the E-model (ITU-T Recommendation G.107),

The E-model has to extended to wideband to meet the requirements described.

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The answer

Is an extended1 E-model!

1 Applicable to both narrowband and wideband voice

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The ITU-T E-model An important tool for definition of CoS

The initial work was carried out as a joint activity between the ETSI STCs BTC2, TE4 and TM5 with TM5 being the lead STC. ETR 250 was published in 1996.

The model has been adopted and refined by ITU-T SG 12. The aim is to give realistic, practical guidance rather than a

scientifically exact treatment of quality factors.(Scope of ETR 250)

The present version of the E-model is not addressing voice over IP, however, it is used in VoIP standards by both TIA and ETSI.

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Extension of the E-model to cover wideband telephony In the introduction of ETR 250 it is stated:

It (the ETR) may later be extended to cover non-handset telephony and wideband (7 kHz) telephony.

ITU-T SG 12 is studying extensions of the E-model, One of the items of ITU-T Q8/12 is:

Investigation of the effects of wide-band transmission on ‘speech sound quality’ and speech communication quality.In 4 years there has been no progress!

Important questions are:– Is the approach the right one?

– What can be done to speed up the process?start

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Available wideband standards

ITU-T Recommendations P.311 and P.341 specifies the transmission characteristics of wideband handset and hands-free terminals,

Annex G to ITU-T Recommendation P.79 defines the wideband loudness rating calculation algorithm,

butThere is a significant gap in the wideband voice standardisation compared with the narrowband voice standardisation.

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Discussion of the elements of the E-model The E-model:

R = Ro – Is – Id – Ie + A Due to the extended low frequency bandwidth it is likely that

Ro will be influenced by the room noise, Among other factors Is is influenced by the actual codec, The effect of delay on speech interactivity is probably not

different for wideband speech compared with narrowband speech. However, the echo effects might be a challenge, particularly because the echo characteristics probably are different for a wideband terminal.

The equipment impairment factor Ie is codec related

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The path…

Wideband and narrowband should be considered as a single case, wideband should not be a special case.

It is recommended to approach to problems on a step-by-step basis,

To make a tool available as soon as possible, an intermediate phase is implemented,

An analysis phase identifies elements of the E-model that are not affected by bandwidth and sets up a priority list for those elements that have to be modified,

An implementation phase where the extended (all-purpose) E-model is developed.

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The steps

The equipment impairment factor of relevant wideband codecs should be estimated using the principles of ITU-T Recommendations P.833 or P.834,

A wideband advantage factor is introduced as an intermediate tool,

The intermediate all purpose (narrowband and wideband) E-model: R = Ro – Is – Id – Ie + A + WBa

The elements of the E-model are analysed. Those that need modifications to include wideband are identified,

A priority list is set up, The required extensions to the E-model are implemented,

following the priority list.

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The intermediate wideband E-model The performance is estimated using,

– The existing E-model,– The equipment impairment factor of the wideband codec

used,– The wideband advantage factor,

This model could be described using one of the following alternatives,

– An Annex to ITU-T Recommendation G.107,– A supplement to the ITU-T G-series Recommendations,– An ETSI Technical Report.

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Sometimes our best is simply not enough……

We have to do what is required.Sir Winston Churchill

Thank you!