ATIS - Alliance for Telecommunications Industry Solutions
Scope
"Echo cancellers are adaptive signal processors used to control echo; they are expected to replace echo suppressors in modern telecommunication networks. Echo cancellers are increasingly present on nearly every long distance connection and may be encountered singly or in tandem on a given connection. This technical report represents the current T1 views on network echo cancellers. These views may change in the future. As a result of the recent reorganization of the International Telecommunication Union (ITU)@ the CCITT was restructured and its name changed to the Telecommunication Standardization Sector (ITU-T). To avoid confusion@ the old nomenclature has been retained throughout this report. Purpose The purpose of this technical report is to: explain the general principles of the operation of echo cancellers; identify a limited set of application rules and the constraints under which echo cancellers operate; explain the relationship among the roles of the planners of a Public Switched Telecommunications Network (PSTN)@ modem manufacturers@ private network planners@ and end users regarding the control of echo (from sources inside and outside the PSTN) and the associated terminal design considerations; identify how echo cancellers may affect the perceived quality of speech@ the quality of voiceband data@ as well as the performance of various signal processing systems (such as digital and packetized circuit multiplication systems); identify both public and private network changes that may require additional study of echo cancellers@ to fully understand how these changes may impact the functionality of present echo cancellers; and explain how new services@ if accepted for implementation@ could have an evolutionary impact on echo canceller design. Application This technical report is limited to echo cancellers that have a digital input and digital subtractors. CCITT refers to these as Type C echo cancellers. In writing this report@ the purpose of Committee T1A1.6 was not to develop a standard@ but to make the technical information on echo cancellers available to the telecommunications industry. Accordingly@ the use of ""should"" or ""recommend"" throughout the report is not to be construed as implying any requirements. Readers may wish to contact Committee T1A1.6 for any updates prior to using the information in this report."