TBR21 is a European telecommunications standard published by

ETSI The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...

, and is the standard to which all telephone equipment must adhere to, to be allowed connection to Europe's

public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...

. It is somewhat equivalent to the US

part 68 'Title 47 CFR Part 68'' is a section of the Code of Federal Regulations of the United States that regulate the direct electrical connection of telecommunications equipment and customer premises wiring with the public switched telephone network, c ...

standard. TBR-21 has been replaced by the new ETSI standard ES 203-021 The "advisory notes" (ATAAB notes) are no longer being maintained.

References

Telecommunications standards {{Measurement-stub