Lower Layer Protocol

This section describes the two supported envelope types used in the HL7 protocol:

• HLLP (Hybrid Lower Layer Protocol)

• MLLP (Minimal Lower Layer Protocol)

Both envelope types use the following configuration parameters. For more information on these parameters, see Lower Layer Protocol — TCP/IP HL7 V2 Inbound Adapter or Lower Layer Protocol — TCP/IP HL7 V2 Outbound Adapter.

• Start Block Character

• End Data Character

• End Block Character

MLLP

The MLLP envelope consists of a Start of Block component, a Data component, an End of Data component, and an End of Block component. The size of the HL7 Data field is determined by the length of the data (number of bytes between start and end), with a maximum size of 99999 Bytes.

HLLP

The HLLP envelope consists of a Start of Block component, a ”D’ (Data) or ”N’ (NAK) indicator, an HL7 Version component, a Carriage Return, a Data component, a Block Size component, a Block Checksum component, an End of Data component, and an End of Block component. The size of the HL7 Data field is determined by the length of the data (number of bytes between start and end), with a maximum size of 99999 Bytes.