FIELD: data transmission equipment. SUBSTANCE: method, which uses processor or digital signal processor, involves reception of test signal, which typically contains noise and other distortion types, in particular, group-delay distortion. Then, method involves detection of variation of group-delay distortion either directly or indirectly as correlation of amplitude distortion or as correlation of selected transmission emphasis filter, as defined in V. 34 protocol. Then, variation of group-delay distortion is used for prevention or prohibition of certain character transmission rates and respective carrier frequencies for detection of optimal character transmission rate and carrier frequency for data transmission and reception. EFFECT: optimal throughput capacity of channel. 10 cl, 9 dwg
