Recommendation V.25 (11/1988): Automatic answering equipment and/or parallel automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices...
superseded recommendation/international standard from the International Telecommunication Union
ITU Telecommunication Standardization Sector
Automatic answering equipment and/or parallel automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls