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.