A first communication node (110) receives a stream of code blocks from a second communication node (120) over an acknowledged connection (131.). The first communication node processes the received code blocks in accordance with at least one transport format parameter, TFP, detects errors in received code blocks, and transmits an acknowledgment in respect of groups of code blocks indicating whether at least one error was detected in the group. A first subset of the code blocks of a group are transmitted (e.g., modulated and demodulated) in accordance with a first TFP value, and a remainder of the code blocks are transmitted in accordance with a second TFP value. Because the first and second TFP values are independent, it is possible either to shorten the necessary processing time in the first communication node or, in connection with a predictive acknowledgment mechanism, to make the receiving-side processing of code blocks that do not contribute to the value of the transmitted acknowledgment more robust.