Echo Suppressor Design Considerations

The growth of telephone circuits with long propagation times, particularly those using synchronous satellite facilities, has renewed interest in the design of echo suppressors. The increase in delay intensifies potential degradations associated with the use of echo suppressors and demands echo suppressor performance far superior to that of older designs. Several organizations, including the Bell System, have designed long delay echo suppressors in the last few years and others are likely to become involved in the future as the growth of long delay facilities increases. Echo suppressors of different design will often be used in the same connection and must be compatible. To assure this compatibility a working party of the International Telephone and Telegraph Consultative Committee (CCITT) Study Group XV, with the cooperation of many of the organizations presently concerned, has recently completed a recommendation on the operating characteristics of long delay echo suppressors. This paper will present the operating characteristics of the newest Bell System echo suppressors, the reasons for them, and the relevant provisions of the CCITT working party recommendation. It is believed that all echo suppressors having these characteristics will perform sufficiently well and be compatible with any other so designed.