Table of Contents

�1���� Scope��
�2���� References
�3���� Terms and definitions
������� 3.1���� acoustic echo��
������� 3.2���� cancelled end��
������� 3.3���� combined loss (ACOM)
������� 3.4���� comfort noise��
������� 3.5���� composite echo��
������� 3.6���� convergence��
������� 3.7���� convergence time��
������� 3.8���� double-talk
������� 3.9���� echo canceller
������ 3.10���� echo cancellers in tandem���
������ 3.11���� echo path��
������ 3.12���� echo path capacity (∆)
������ 3.13���� echo path delay (td)
������ 3.14���� echo return loss (ERL) (AECHO)
������ 3.15���� echo return loss enhancement (ERLE) (ACANC)
������ 3.16���� electric echo��
������ 3.17���� H register
������ 3.18���� H register reset
������ 3.19���� leak time��
������ 3.20���� non-cancelled end��
������ 3.21���� non-linear processor (NLP)
������ 3.22���� non-linear processing loss (ANLP)
������ 3.23���� open echo path��
������ 3.24���� pure delay (tr)
������ 3.25���� residual echo level (LRES)
������ 3.26���� returned echo level (LRET)
������ 3.27���� signal processing device (SPD)
������ 3.28���� signal processing function (SPF)
������ 3.29���� signal processing network equipment/element (SPNE)
�4���� Abbreviations and acronyms
�5���� Test signals
�6���� Characteristics of echo cancellers
������� 6.1���� General
������� 6.2���� Purpose, operation and environment
������� 6.3���� External enabling/disabling
������� 6.4���� Tests and requirements for performance with input signals applied to the send and receive paths����
�7���� Characteristics of an echo canceller tone disabler
������� 7.1���� General
������� 7.2���� Detector characteristics
������� 7.3���� Guardband characteristics
������� 7.4���� Holding-band characteristics
������� 7.5���� Operate time��
������� 7.6���� False operation due to speech currents
������� 7.7���� False operation due to data signals
������� 7.8���� Release time��
������� 7.9���� Other considerations
�8���� Non-linear processors (NLPs) for use in echo cancellers
������ �8.1���� Scope��
������� 8.2���� General principles and guidelines
Annex A � Description of an echo canceller reference tone disabler����
Annex B � Description of a reference non-linear processor����
������� B.1���� General
������� B.2���� Suppression threshold (TSUP)
������� B.3���� Static characteristics of activation control
������� B.4���� Dynamic characteristics of activation control
������� B.5���� Frequency limits of control paths
������� B.6���� Testing
Annex C � Composite source signals for testing of speech echo cancellers � Signal, description and analysis����
������� C.1���� Introduction��
������� C.2���� Composite source signal � General considerations
������� C.3���� Bandlimited composite source signal with speech like power density spectrum � Practical realization for measurements of echo cancellers����
������� C.4���� Appropriate analyses to determine convergence characteristics of speech echo cancellers using the composite source signal����
Annex D � Echo-path models for testing of speech echo cancellers����
������� D.1���� Introduction��
������� D.2���� Echo path models from network hybrid simulator
������� D.3���� Echo path models measured from telephone networks in North America
������� D.4���� Echo path models measured from telephone networks in Europe��
Annex E � Embedded Echo Cancellers (EECs)����
������� E.1���� Scope��
������� E.2���� Definitions
������� E.3���� EEC requirements
����� Page
������� E.4���� EEC testing
������� E.5���� Special considerations
Appendix I � Guidance for application of echo cancellers����
������� I.1���� Scope��
������� I.2���� Echo control in the public switched telephone network
������� I.3���� Application rules and operational constraints
������� I.4���� Effect of cancellers on voice and data services
������� I.5���� High-level speech��
������� I.6���� Network and service evolutionary considerations
������� I.7���� Considerations regarding echo canceller performance during double talk
Appendix II � Measurement methods for characteristics of echo paths����
������ II.1���� Introduction��
������ II.2���� Measurement procedure
������ II.3���� Analysis of echo-path characteristics
������ II.4���� Examples of echo path measurements from real networks
������ II.5 ����Conclusions
Appendix III � Multiple tail circuits����
Appendix IV � Guidelines on the use of parameters for testing echo cancellers����
Appendix V � List of low speed modems for optional use with Test No. 14����
Appendix VI � Example control interfaces����
������ VI.1���� Parallel transistor-transistor logic (TTL) connection for digital signals
������ VI.2���� Serial data link (ITU-T V.24 or RS-232) for software commands
Appendix VII � Guidance on echo canceller orientation in conference bridge applications����
����� VII.1���� Introduction��
����� VII.2���� Echo canceller oriented towards the hybrid of the conference bridge participant (recommended)����
����� VII.3���� Echo canceller oriented away from the hybrid of the conference bridge participant (not recommended)����
Appendix VIII � Test methodologies for use on embedded echo cancellers����
���� VIII.1���� Introduction��
���� VIII.2���� Test Methodology 1: Testing with the aid of a special "Test Mode" (under study)
���� VIII.3���� Test Methodology 2: Testing without access to control signals (under study)
Bibliography����