MLLP Send Adapter Processing

The Minimal Lower Layer Protocol (MLLP) send adapter supports one-way and two-way transport modes in the following configurations:

• Two-way solicit-response send adapter

• One-way send adapter configured to receive acknowledgments (ACKs)

• One-way send adapter configured for no return messages

Two-way solicit-response send MLLP adapter

Use this adapter in a true end-to-end synchronous scenario. As such, you can only use this adapter with one destination party. The send adapter will continuously maintain an open connection against the remote party (URL) until it routes a return message to the request response receive port. See the following diagram for the architecture of request response/solicit response processing.

When you use this adapter, you can direct the system to return either an ACK or a response message to the line-of-business application. You do so with the Route ACK to Send Pipeline on Request Response Receive Port setting in the BTAHL7 Configuration Explorer. Select this property to return an ACK, or deselect it to return a response meeting.

Once a send port using this adapter has successfully sent the original message, BTAHL7 deletes that message. The receive pipeline associated with this send port will not generate an ACK. BizTalk will forward the query response to the source application regardless of the value of the MSA2 field of that response.

One-way send MLLP adapter configured to receive ACKs

This adapter receives ACKs on the same socket connection that it sends the original message on, and delivers the ACKs to the receive location. The send adapter continuously maintains an open connection against the remote party (URL), even if no messages are waiting for BizTalk Server to send them to it. If several ports are pointing to the same remote party, the send adapter maintains one connection for each send port.

Microsoft BizTalk Accelerator for HL7 (BTAHL7) setup installs a default receive location, TwoWayAckReceiveLocation. You can use this receive location with the MLLP send adapter for receiving ACKs. This configuration of the send port using this adapter requires you to associate a receive location with the send port.

Use this send port if you are set up to receive a response message with an MSA field, or to support multiple destinations. The two-way solicit-response adapter does not work with the MSA field or with multiple destinations.

Acknowledgments received by the one-way MLLP send adapter

When a one-way MLLP send adapter configured for ACKs receives one, BizTalk Server deletes the original message from the MessageBox database, retries it, or suspends it, depending on the type of the ACK. BTAHL7 parses the ACK in two phases:

• The first phase is done in the send adapter where BTAHL7 parses the field MSA1 to determine the type of the ACK.

• In the second phase, BTAHL7 performs a complete parsing of the ACK, and then submits the ACK to the MessageBox database.

  You configure the ACK that the two-way send adapter expects in BTAHL7 Configuration Explorer.

  The following table shows the ACKs that an MLLP send adapter can receive and the resulting action on the original message.

ACK received	Action on the original message
Commit Accept, or Application Accept	Delete from the MessageBox database
Commit/Application, Reject ACK, or Invalid ACK	Suspend
Commit/Application Error	Retry/Move to backup transport/Suspend
Static ACK Success	Delete from the MessageBox database
Static ACK Failure	Suspend

The following table shows ACK conditions that are not valid.

Instance	Condition
HL7 (Original, Enhanced, Deferred)	1. Does not contain XML. 2. Does not have the structure so the MSA1 field cannot be retrieved; or the MSA1 field does not contain one of the permissible values (CA, AA, CR, AR, CE, AE).
Static	Does not match one of the permissible values for success or fail ACK.
Contains XML	Treated as an Acceptance ACK (regardless of the content) and deleting the original message.

Error Conditions

The following can occur when there is an error condition or inactivity:

• If the outgoing message fails in serialization, the send adapter will not send the message, unless it is a batch message that BTAHL7 is streaming. If that is the case, and BTAHL7 detects a serialization failure halfway through the message, the adapter will not send EB/CR since BizTalk Server has not sent the complete message. The pipeline logs an error, and the adapter tries to send the batch message again.

• If a send operation fails, the adapter tries to send the message again, up to the number of retries specified in the send-port configuration settings. After exhausting the retries, the message moves to the backup transport, if one exists. If all else fails, the message is suspended. The suspended message will be in the original (XML) form.

  BTAHL7 can generate the following events to describe the error conditions:

Event	ID	Error Condition
ErrorSendingMessage	8450	Could not send a message to the remote party. The most common reasons are network failures or timeouts. BTAHL7 may report this error if the send pipeline fails while serializing a large message.
ErrorReceivingAck	8451	Could not receive an acknowledgment, due to network failure or timeout.
ErrorConnecting	8453	Could not establish a TCP connect to the remote party—the host name could not be resolved, or the remote party is not listening on the port or is rejecting the connections.

Note

The configuration of the destination party (in MSH5 of the original message) determines whether BTAHL7 expects an HL7 or static ACK. In case of a mismatch, BTAHL7 treats the ACK as not valid.

After the MLLP send adapter processes an ACK, the ACK is delivered to the receive location as a message on its own. The disassembler performs full parsing of the ACK, which may result in parsing errors being reported by the receive pipeline and/or the ACK being suspended.

See Also

Processing MLLP-encoded Messages
Configuration Parameters for Send and Receive Adapters
MLLP Receive Adapter Processing
Setting Up a Send Port for Receiving ACKs