Sequence numbering of normal-flow RUs is done for each direction of flow for an LU type 0 session. For certain types of 3270 LUs, the sequence number wraps to 0 after it reaches 255; for all other LUs, the sequence number wraps to 0 only after it reaches 65 535. The application program must always use the full 2-byte sequence number field for any comparisons (for example, when trying to match a response with a previously sent request) and should not be coded to be sensitive to the point at which the sequence number wraps.