MLLP Receive Adapter Processing
The Minimal Lower Layer Protocol (MLLP) receive adapter supports both one-way and two-way request response modes. The adapter listens and accepts connections.
When the MLLP receive adapter operates in two-way mode, the adapter will not receive a new message from the connection until the pipeline has generated the acknowledgment (ACK) for the previous message.
Configuration Parameters
The parameters for a receive handler are configured at the BizTalk Host level, and apply to all MLLP receive locations associated with it.
| Parameter | Use |
|---|---|
| Max Accept Connection Limit | Limits the number of concurrent open connections that the receive adapter will accept. |
Acknowledgments with the two-way MLLP receive adapter
When a two-way MLLP receive adapter receives a message, Microsoft BizTalk Accelerator for HL7 (BTAHL7) can generate the following types of ACKs:
HL7 Enhanced Commit ACK: In this scenario, BTAHL7 sends a Commit ACK on the same connection. It sends out an Application Accept ACK on a different send port.
Application Accept ACK: In this scenario, BTAHL7 sends an Application Accept ACK on the same connection.
Static ACK: In this scenario, BTAHL7 sends an ACK on the same connection.
The type of ACK generated depends on the BTAHL7 Configuration Explorer settings for the party sending the message. The value in fields MSH 15 and 16 of an individual message can override this setting. However, for applications expecting Static ACKs, the configuration can only be set through BTAHL7 Configuration Explorer.
Error Conditions
The following events occur when there is an error condition or inactivity:
If the receive location is disabled or BizTalk Server shuts down, the following occurs:
The receive location will no longer accept new connections.
For existing connections, BizTalk Server completely receives the current message, and then closes the connection.
When inactivity is detected (no payload data received on the receive location within the specified timeout), the adapter closes the connection.
If BizTalk Server receives an incomplete message, the portion received is suspended. All bytes received outside of a message (before the first SB on a new connection, between EB/CR and SB of the next message) are ignored.
If the pipeline fails to parse the message, the message is still delivered to the MessageBox database, with a promoted property ParseError=true.
If a message fails due to the absence of a subscription, or due to structural errors in the header, BizTalk Server suspends the message in its original "wire" form (prior to being parsed). A frequent reason for the no-subscription failure is the lack of promoted properties. Since BizTalk Server suspends the unparsed message, the BTS.MessageType will be blank.
The following table lists the errors that the MLLP receive adapter returns.
| Event | ID | Error Condition |
|---|---|---|
| ErrorListening | 8448 | Could not bind to a local socket (most likely some other local application is using the same IP address/port ID combination). |
| ErrorAcceptingConnection | 8449 | Could not establish a TCP connection with the remote party. Either BizTalk Server reached the maximum connection limit, or the resources were insufficient. |
| ErrorSubmittingMessage | 8452 | The MessageBox database could not accept the message. Either SQL Server was unavailable or the resources were insufficient. |
| ErrorSendingAck | 8454 | BizTalk Server could not return the acknowledgment because the connection was not available. |
Performance Counters
The following table lists the performance counters that the MLLP adapter uses.
| Counter | Meaning |
|---|---|
| Bytes | Size of the payload of all documents received or sent. |
| Bytes/sec | Current throughput of the payload received or sent. |
| Documents processed | MLLP Receive: Number of documents successfully delivered to the MessageBox database. MLLP Send: Number of documents successfully delivered to the remote application. |
| Documents failed | MLLP Receive: Number of documents not successfully delivered to the MessageBox database. MLLP Send: Number of documents not successfully delivered to the remote application. |
| Connection status | The status of the adapter connection, 1 or 0 (1=connected). |
The performance counter instances use the following naming scheme:
{recv|trans} : connection name : remote IP address : remote port ID
Where the MLLP receive adapter uses the "recv" prefix, and the MLLP send adapter uses "trans".
Note
ACKs sent by receive ports (for example, an adapter operating in a two-way mode) and send ports (operating to receive ACKs on the same socket connection) are not counted.
See Also
Processing MLLP-encoded Messages
Configuration Parameters for Send and Receive Adapters
MLLP Send Adapter Processing
Setting Up a Send Port for Receiving ACKs