Calculation and transmission of error check codes

A method of transmitting data (1) generated in an upper layer protocol such as iSCSI in a transport protocol such as TCP or SCTP, without requiring separate reads for check code generation and transmission. The upper layer protocol data is read into a transmission engine (5) that calculates the error check codes and inserts them into the transport protocol transmission. To prevent having to recalculate error codes in the event of loss of transmitted data and a retransmission request, the engine preferably also writes the error check codes into the memory so that the can be retrieved if retransmission is necessary.