TBR21 explained

TBR21 is a European telecommunications standard published by ETSI, and is the standard to which all telephone equipment must adhere to, to be allowed connection to Europe's public switched telephone network.^[1]

It is somewhat equivalent to the US part 68 standard.

TBR-21 has been replaced by the new ETSI standard ES 203-021^[2]

The "advisory notes" (ATAAB notes) are no longer being maintained.

Notes and References

1. Web site: Nemko USA, Inc. Ts.nist.gov. 31 May 2019.
2. Web site: ETSI ES 203 021-1 V2.1.1 (2005-08) : ETSI Standard Access and Terminals (AT); Harmonized basic attachment requirements for Terminals for connection to analogue interfaces of the Telephone Networks; Update of the technical contents of TBR 021, EN 301 437, TBR 015, TBR 017; Part 1: General aspects. PDF. Etsi.org. 31 May 2019.