HL7 Messages are used to transfer electronic data between disparate healthcare systems. Each HL7 message sends information about a particular event such as a patient admission. There are two types of Acknowledgement messages (ACKs) used in healthcare data exchange communications: HL7 ACKs include original mode acknowledgements and enhanced mode acknowledgements, and non-HL7 ACKs, also known as static string acknowledgements.

An HL7 ACK is created with information from the HL7 message, and is in the following HL7 formats.

Original Mode Acknowledgement: This acknowledgement is a "Receive" ACK. It indicates that a message has been received but not necessarily processed yet.
Enhanced Mode Acknowledgement: This acknowledgement is an "Application" ACK that is a resultant status return rather than a communication response, such as an order response.

Original Mode Acknowledgements include the following HL7 acknowledgements:

Application Accept (AA) acknowledgement. The message was accepted without error.
Application Error (AE) acknowledgement. The message had an error and was rejected.
Application Reject (AR) acknowledgement. The message was rejected because of an error.

Enhanced Mode Acknowledgement include the following HL7 acknowledgements:

Application Accept (AA) acknowledgement. The message was accepted without error.
Application Error (AE) acknowledgement. The message had an error and was rejected.
Application Reject (AR) acknowledgement. The message was rejected because of an error.
Commit Accept (CA) acknowledgement. The message was accepted by the backend system.
Commit Error (CE) acknowledgement. The message had an error and was rejected by the backend system.
Commit Reject (CR) acknowledgement. The message was rejected in the backend system because of an error.

The MLLP service will send an acknowledgement once it receives the message from client. If the message was accepted without error, it will send AA acknowledgement to the client and save the message in the

userdata/MLLP/ListenerName

folder. The saved message name will be in the format

msg_(Client)IP_(Client)Port_Timestamp

. It will create the service event "

MLLP Message received successfully

".

If the message had validation error and was rejected, it will send an AE acknowledgement to the client and save the message in the

userdata/MLLP/<ListenerName>

folder. The saved message name will be in the format

err_msg_(Client)IP_(Client)Port_Timestamp

. It will create an "

MLLP Message received failed

" service event.

If the message was rejected because of an error such not having write permission to the

userdata/MLLP/ListenerName

directory, it will send AR acknowledgement to the client. It will create an "

MLLP Message received failed

" service event.