(Continuation of Question 7/15 and part of Question 5/15)
Background and justification
This Question deals with network-based speech enhancement
devices, including electrical network echo control, acoustic
network echo control, automatic level control devices, and speech
enhancement devices for wireless networks.
The application of echo cancellers continues to evolve in
existing PSTN, cellular, and emerging ATM and IP networks. These
applications can bring new issues to echo canceller performance,
and will require study to ensure that administrations have
adequate assurance of transmission quality with echo cancellers
complying with G.168. These issues may result in adding and
improving the tests within G.168, and studying the issues arising
from the deployment of echo cancellers to ATM and IP networks and
new services within the PSTN/GSTN.
There is also a need to address equipment-related issues
associated with echo cancellers such as; defining appropriate
interfaces of echo cancellers, alarming requirements, power
requirements, and the possible integration of automatic level
control and other speech enhancement functions into echo
cancellers.
The deployment of Automatic Level Control Devices is just
beginning, and new issues are expected to arise as these devices
are applied to existing and emerging networks. As a result, G.169
may need to be revised to ensure adequate transmission quality.
Wireless echo cancellers and speech enhancement devices are being
deployed in cellular networks to improve the performance of mobile
applications. There is consequently a need for a new
Recommendation to cover the performance requirements of these
devices.
Responsibility under this Question includes the G.16x series of
Recommendations and those aspects of the G.776 series that deal
with the operation of echo cancellers.
Question
- What functional characteristics and requirements are
necessary for network-based speech enhancement devices to
provide good performance in existing GSTN and emerging ATM/IP
and cellular networks?
- What requirements are necessary for the equipment-related
aspects of network-based speech enhancement devices?
- What management interfaces should be recommended for speech
enhancement equipment?
Study items
Study items to be considered include:
- The enhancement of objective tests to better correlate with
subjective test results
- The effect of impairments, including level and PCM offset,
poor natural echo return loss, noise, and possible phase roll on
the performance of echo cancellers and speech enhancement devices
- Tests and requirements necessary to ensure good double-talk
performance of echo cancellers. These tests may cover
measurement of clipping level variations and echo during doubletalk
- The effect of tandem echo cancellers
- The effect of low bit rate coders and other non-linearities
in the echo path of echo cancellers
- The performance of speech enhancement devices with facsimile
and voice-band data signals, signalling tones, call-processing
tones, speech, etc.
- The performance of speech enhancement devices in cellular and
other wireless environments.
- The performance of the non-linear processor in an echo canceller
- Background noise transmission through speech enhancement devices
- Performance issues relating to the interaction of ISDN,
B-ISDN, ATM, IP and cellular networks with the PSTN
- Management interfaces to speech enhancement equipment
- The control of speech enhancement devices by external devices
- The performance of automatic level control and speech
enhancement devices in PSTN/GSTN ATM/IP and cellular networks
- The effects of residual acoustic echoes on the performance of
the network echo canceller
- Hardware and software tools necessary to support the testing
of speech enhancement devices
- Realistic echo paths and test signals required for testing
speech enhancement devices
- Trade-offs between echo path delay, convergence quality, and
convergence time of an echo canceller
- The impact of evolving terminal equipment such as modems,
fax, and multimedia terminals on speech enhancement devices
- Performance issues relating to far-end echo cancelling and
far-end delay build-out
- The simplification and repeatability of performance tests for
speech enhancement devices and the ability of these tests to be
independent of different manufacturers’ implementations and to
represent real-world network operation
- The effect of clock differences between the receive and send
paths of an echo canceller
- The effect of tandem coding avoidance (vocoder bypass or TFO)
on in-path SPNE
Specific tasks
- Revise Recommendation G.168 by 2002 and Recommendation G.169 by 2004
- Develop draft new Recommendation(s) on equipment aspects of
speech enhancement devices by 2002
- Develop draft new Recommendation on speech enhancement
functions associated with wireless networks by 2002
- Develop draft new Recommendation on acoustic network echo
controllers not associated with wireless networks by 2004
- Develop guidelines for the application of speech enhancement
devices to be included in the respective Recommendations above
Relationships
- Other SG 15 questions as relevant
- ITU-T SG 4 on TMN aspects
- ITU-T SG 8 on facsimile
- ITU-T SG 11 on signalling issues
- ITU-T SG 12 on application guidelines and subjective performance
- ITU-T SG 13 on ATM and IP issues
- ITU-T SG 16 on multimedia issues
- ATM Forum and IETF
- ITU-R SG4 WP4B on voice on mixed terrestrial/satellite networks
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