Data communication apparatus and method

A data communication apparatus having a message receiver and a message transmitter, wherein when transmitting a message to the receiver 900, the message transmitter partitions payloads greater than a predetermined size into a set of plural successive messages 910, each no larger than the predetermined size. One or more flags indicating an ordering of the messages within the set are associated with respective ones of the set of messages 920. The message receiver has a buffer which upon receiving the set of plural successive messages reassembles the payload represented by the set 930, and a detector which detects an expected ordering of the one or more flags associated with the received set of messages 940. The flags may include a start flag indicative of a first message in the set, and an end flag indicative of a last message in the set and an error condition may be indicated in response to a detection that the flags have been received in an unexpected order. The apparatus may be a message handling unit (MHU).