The invention relates to a method whereby the control unit produces a sequence of blocks, each comprising a header and data to be transmitted. Each block is transmitted to the destination terminal with a level of error protection which is selected from among several pre-defined levels, the selected level being indicated in a piece of signalling information that accompanies the block transmitted. The header of each block comprises an acknowledgement control field which is activated intermittently by the control unit in order to request an acknowledgement of blocks from the terminal. A higher level of protection is selected for transmitting blocks having a header with an activated acknowledgement control field than for transmitting blocks having a header with a non-activated acknowledgement control field.