The Minimal Lower Layer Protocol (MLLP) protocol is used to transfer healthcare industry messages, such as HL7 messages. HL7 is a messaging specification for healthcare information systems. The MLLP protocol has a long history of use with HL7 standard messages, although it has never been formally part of the HL7 standard itself. The MLLP protocol is a minimalistic OSI-session layer framing protocol. HL7 is a messaging specification for healthcare information systems.