STQ Activity Report 2012

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Acting Chairman:
Jean-Yves Monfort
    STQ is ETSI’s technical committee for Speech and multimedia Transmission Quality. It was formed in 1997 combining interests from the former BTC2, TE4 and TM5 areas of ETSI. It was intended initially as a centre of expertise on speech quality issues but has broadened its scope to handle more general quality issues.

STQ has over 100 members several of whom also play leading roles in ITU-T.

STQ has three main areas of activity:

  • Speech quality and end-to-end speech transmission performance
  • General quality of service parameters for fixed and mobile networks
  • Distributed speech recognition algorithms (the Aurora project)

Speech transmission and quality

Speech transmission is important and has been topical for the last decade because of two major changes in telecommunications.

First liberalization and competition have been changing the framework for telecommunications such that responsibilities for end-to-end speech transmission performance are no longer clear and it is no longer possible to use a single simple reference model for connections. STQ has continued work to address these issues by using the  E-model and by developing guidance on network design. STQ originally developed the principle that the service provider or operator who charges the customer should be responsible for the transmission quality of the segment of the connection for which the charge is made. This principle has been accepted generally by regulators in Europe. Work is continuing for the maintenance of the E-Model which has been adopted by the ITU-T as the principle tool for predicting voice quality.

Secondly, just when digital circuit switched technology was becoming universal with the prospect of making planning much easier, the impending change to IP technology is raising important new issues such as call set-up time, echo control and cell loss which affects codecs. STQ members are working actively on these issues in ETSI TISPAN . STQ decided that it would be more effective for its members to attend and work within TISPAN rather than to work separately. This arrangement has worked well and ensured a good transfer of knowledge about speech quality into TIPHON and of knowledge of IP and NGN into STQ.

STQ works closely with the TR-41 committee of the Telecommunications Industry Association (TIA) of North America, with members of each committee attending the other as guests. This cooperation is proving successful in gradually harmonizing the terminology and more recently the methodology for transmission planning for private and corporate networks. Relations have also been established with standardization bodies in the Asia Pacific region and with the NATO defence community.

STQ has recently created an active Working Group for the testing of Quality of Service of Mobile services including new IP based services. The group has 50 active participants and has created a work programme covering QoS aspects for popular services in GSM and 3G networks.

STQ has performed work on acoustic pressure issues for terminal equipment. A preliminary report reviewing the published material is proving extremely popular and work is now ongoing on performance limits for excessive levels and test methods.

General quality of service parameters

During 1999 STQ revised extensively the definitions and measurement methods of the quality of service parameters that have to be reported by public network operators with significant market power under the Voice Telephony Directive (98/10/EC). These parameters are:

  • Supply time for initial connection
  • Fault rate
  • Fault repair time
  • Unsuccessful call ratio
  • Call set-up time
  • Response times for operator services
  • Response time for directory enquiry services
  • Public pay-telephones in working order
  • Bill correctness complaints

NOTE:     The Voice Telephony Directive has been repealed. It is now necessary to refer to the Universal Service Directive (2002/22/EC) and the Access Directive (2002/19/EC).

Amongst the changes made were measuring supply time and fault repair time in elapsed days/hours instead of working days/hours to give a clearer indication of the effect on customers and introducing distinctions as necessary for direct and indirectly connected services.

STQ is currently finalizing  two multipart standards on QoS parameters and measurement methods. The first is on user related parameters starting with parts on general parameters and parameters for telephony, fax and modem data services. The second is on parameters for network to network interconnection, starting with parts on narrowband circuit switched services and local loop unbundling. The work on interconnection is breaking new ground and attracting interest because interconnection agreements need to specify QoS parameters and some regulators are likely to require reporting on performance. Number portability is amongst the issues that will be covered.


STQ has a well attended working group called AURORA that meets independently to develop and standardize algorithms for distributed speech recognition (DSR) that enables access to services and communication systems without the need to type or use a keypad. The basic algorithm (to be found in ES 201 108) enables speech to be sent over low quality links such as mobile radio and converted to text for interacting with automated systems. The quality degradation of the links makes it necessary to perform a certain amount of pre-processing at the front end in the mobile terminal and send the results across the link for subsequent processing in the network.

The value of DSR is that it provides substantial recognition performance advantages compared to a conventional mobile voice channel where both the codec compression and channel errors degrade performance. It also enables new mobile multimodal interfaces by allowing the features to be sent simultaneously to other information on a single mobile data channel such as GPRS. 

AURORA has also published two important Extended Distributed Speech Recognition (DSR) Standards as extensions to the existing specifications, which provide the front-end feature extraction suitable for use by speech recognizers. ES 202 211 is the extension to the DSR mel-cepstrum standard (ES 201 108) and ES 202 212 is the extension to the DSR Advanced Front-end (ES 202 050).

The extensions make use of the same recognition features and give additional functionality. An extra 800 bps of data, providing pitch and voicing class, are sent alongside the 4800 bps for the features.

The publication of these DSR extensions completes standardization of the full DSR capability. We look forward to seeing widespread deployment over different networks to bring new speech and multimodal services particularly for access to information on handheld mobile devices (Smartphones or PDA’s) and in vehicles”.

The DSR Extended Advanced Front-end (ES 202 212) is being integrated by 3GPP working group SA4 as the SES (Speech Enabled Services) codec. DSR should have widespread application in future mobile systems and will also be usable over Internet.

The Aurora Concept

Seminars and workshops

STQ takes its role as a centre of expertise rather than a project team seriously, and spends a significant part of its time following new developments and organizing special events such as:

  • A workshop in July 2009 on QoS Implications of NGN Architectures
  • A workshop in June 2008 on Effects of transmission Performance on Multimedia QoS
  • A workshop in February 2003 on Compensating for Packet Loss in Real-Time Applications,
  • A workshop in 1999 on speech quality over IP that brought together “lower layer” experts from IETF with “upper layer” experts from STQ and ITU-T,
  • A workshop in 1998 on methods of measuring speech quality where eight different companies gave presentations about their developments,
  • A seminar in 1997 on transmission modelling in memory of Nils Olof Johanesson, the ETSI and ITU expert who developed the E-model for predicting the subjective effect on speech of combinations of transmission impairments.

To view the current situation of ETSI deliverables produced and maintained by ETSI STQ
refer also to the ETSI Work Programme


Last updated: 2010-02-10 09:57:58