Method for data transmission at a transmitter-side data transmission unit comprising the steps: a) receiving a data transmission request for message from a safety-relevant real-time application which is operatively connected to the transmitter-side data transmission unit; b) transmitting a first portion (ω 1, ω 2, ω 3) of the message to a receiver-side data transmission unit via a communication channel for the purpose of determining the availability of the communication channel on the basis of parameters of the communication channel measured during reception of the first portion (ω 1, ω 2, ω 3) of the message and on the basis of estimated parameters of the communication channel for the still available remainder of a predetermined maximum permissible data transmission time for the transmission of the message; c) receiving an availability indicator for the communication channel from the receiver-side data transmission unit as the result of determining the availability of the communication channel; and d) if the availability indicator shows that the communication channel is available, configuring the data of the message yet to be transmitted for a successful transmission within the still available remainder of the maximum permissible data transmission time predetermined by the real-time application for the transmission of the message, and transmitting the data of the message yet to be transmitted, wherein the configuration of the data of the message to be transmitted for the transmission of the remaining message includes: adjustment of the number and length of data blocks of the message yet to be transmitted taking account of transmission repetitions of individual data blocks that are to be expected. a) receiving a data transmission request for message from a safety-relevant real-time application which is operatively connected to the transmitter-side data transmission unit; b) transmitting a first portion (ω 1, ω 2, ω 3) of the message to a receiver-side data transmission unit via a communication channel for the purpose of determining the availability of the communication channel on the basis of parameters of the communication channel measured during reception of the first portion (ω 1, ω 2, ω 3) of the message and on the basis of estimated parameters of the communication channel for the still available remainder of a predetermined maximum permissible data transmission time for the transmission of the message; c) receiving an availability indicator for the communication channel from the receiver-side data transmission unit as the result of determining the availability of the communication channel; and d) if the availability indicator shows that the communication channel is available, configuring the data of the message yet to be transmitted for a successful transmission within the still available remainder of the maximum permissible data transmission time predetermined by the real-time application for the transmission of the message, and transmitting the data of the message yet to be transmitted, wherein the configuration of the data of the message to be transmitted for the transmission of the remaining message includes: adjustment of the number and length of data blocks of the message yet to be transmitted taking account of transmission repetitions of individual data blocks that are to be expected.