MLLP
Minimal Lower Layer Protocol, a TCP-based framing protocol used to transmit HL7v2 messages between healthcare systems.
MLLP wraps each HL7v2 message in a start block (0x0B), end block (0x1C), and carriage return (0x0D). It runs over raw TCP, typically on port 2575. MLLP has no built-in encryption or authentication — TLS must be layered on top (sometimes called MLLPS). Most integration engines (Mirth Connect, Rhapsody, Cloverleaf) support MLLP natively. Despite its simplicity, MLLP connection management (timeouts, reconnects, ACK handling) is a common source of production issues.
FAQ
- Is MLLP secure?
- MLLP itself has no encryption. For secure transmission, wrap MLLP in TLS (sometimes called MLLPS). Many production interfaces still run unencrypted MLLP on private networks, which is a compliance risk.