All termsTransports
TCP / MLLP
Minimal Lower Layer Protocol — the thin framing that wraps HL7 v2 messages over a raw TCP socket, marking where each message starts and ends.
When to use it
The default transport for real-time HL7 v2 feeds between interface engines and clinical systems on a hospital network.
In plain terms
It is the envelope and seal around each HL7 message, so the receiver knows where one letter ends and the next begins.
Common gotchas
- MLLP has no built-in retry, encryption, or persistence — reliability is the engine's job, and security usually means TLS on top.
- An ACK confirms receipt, not that the message was successfully processed or filed.
- Firewall rules must allow the specific port; MLLP holds a persistent TCP connection, not a request/response call.