According to the invention, in order to transmit user data from a source communications device (KE1) provided with a first encoder (CODEC_A, CODEC_B1, CODEC_C) for encoding users data to a target communications device (KE2) provided with a first decoder (CODEC_J2, CODEC_K) for decoding said user data via a communication network which is provided with several converting devices (GW1, GW2, GW3) comprising additional encoders (CODEC_B2, CODEC_D, CODEC_H2,...) and additional decoders (CODEC_B2, CODEC_D, CODEC_H2,...) for carrying out the verification of the converting devices (GW1, GW2, GW3). Said verification consists in determining, whether the first encoder (CODEC_A, CODEC_B1, CODEC_C) is compatible with the decoder (CODEC_B2, CODEC_D, CODEC_H2,...) of a given converting device (GW1, GW2, GW3) and, whether the first decoder (CODEC_J2, CODEC_K) is compatible with the encoder (CODEC_B2, CODEC_D, CODEC_H2,...) of said converting device (GW1, GW2, GW3). One of the converting devices (GW1, GW2, GW3) for which the compatibility is ascertained by the verification is selected for transmitting user data. During transmission of the user data, said user data encoded with the aid of the first encoder (CODEC_A, CODEC_B1, CODEC_C) is decoded with the aid of the compatible decoder (CODEC_B2, CODEC_D, CODEC_H2,...) of the converting device (GW1, GW2, GW3) and the user data decodable with the aid of the first decoder (CODEC_J2, CODEC_K) is encoded with the aid of the compatible encoder (CODEC_B2, CODEC_D, CODEC_H2,...) of the selected converting device (GW1, GW2, GW3).