A method for transmitting data in messages via a communication link of a communication system, as well as a communication module, users of a communication system and a communication system for implementing this method. The messages are transmitted cyclically in specifiable time windows via the communication link, messages sent and to be sent via the communication link initially being stored temporarily in a message memory of a communication module, and the message to be sent or to be received in a current time window being taken from the message memory and sent, or received and stored in the message memory. To improve the real-time capability of the communication module, it is provided that to ascertain the positions of the messages in the message memory, it is searched in advance at regular intervals for, in each instance, a plurality of time windows still following, and as the result of a search run, the positions of the messages to be sent or to be received in the plurality of time windows still following are stored in a buffer assigned to the message memory. Within the course of the actual data transmission, which includes sending or receiving of messages, the buffer is simply accessed, and via the positions stored there, the matching message objects are accessed in the message memory.