Recommendation ITU‑T G.994.1 provides a flexible mechanism for digital subscriber line (DSL) transceivers to exchange capabilities and to select a common mode of operation. It includes parameters relating to service and application requirements as well as parameters pertinent to various DSL transceivers. This Recommendation is currently an integral part of the start-up procedure for Recommendations ITU‑T G.991.2, ITU-T G.992.1, ITU-T G.992.2, ITU-T G.992.3, ITU-T G.992.4, ITU-T G.992.5, ITU-T G.993.1 and ITU-T G.993.2. It is anticipated that future DSL Recommendations will also be able to make use of this Recommendation. Provisions are also included for exchanging non-standard information.

This revision integrates all approved amendments and corrigendum into the latest revision of Recommendation ITU-T G.994.1 (version 3). It also:

fixes the allocation of the codepoint "Support of downstream virtual noise in diagnostic mode"

fixes the allocation of the codepoint "Full ITU-T G.993.5-friendly ITU-T G.993.2 operation"

removes the codepoints for O-P-VECTOR-1-1 duration.