Abstract: Apparatus for transmitting and receiving information blocks, particularly video information, is arranged so that on receiving a corrupted information block it stores a first receiver buffer address at which the data block should be stored if subsequently successfully repeated in a later information block. The apparatus keeps track of the time taken to receive a requested repeat information block and on receiving the later information block at the predicted time, and on determining that it is uncorrupted, stores the data in the receiver buffer at the stored buffer address. Such apparatus can allocate received, repeated and non-repeated data blocks to their correct relative positions within the receiver buffer without the need for numbering of the data blocks on transmission giving a consequential reduction in the size of the data blocks being transmitted.