A programmer can use a LlpClient to send messages out to a remote host via LLP. The component allows only one connection through which messages are sent and received.

Three methods on the LlpClient class are of particular interest:

• connect: Connects to the given host and port number.
• transmitMessage: Sends a message to the server, prefixed and postfixed by the current HeaderBlock and TrailerBlock characters.
• disconnect: Attempts to gracefully disconnect from the server.

By default, the HeaderBlock is set to 0x0B and the TrailerBlock is set to 0x1C followed by 0x0D. These are the standard Lower Layer Protocol (LLP) header and trailer characters.

Event handlers are registered with the LlpClient to handle the asynchronous network events that will all be called back on the thread that the class was created on. An event handler is written by the developer. The five main event handlers used for the LlpClient object are:

• closed: Fired when a connection is closed.
• connected: Fired when a connection is made with the Server.
• dataIgnored: Fired when received data is not within the header and trailer blocks.
• errorReceived: Fired when an error occurs with the TCP/IP connection.
• messageReceived: Fired when a message is received.

If you are implementing an LLP client that is sending HL7 data using the LlpClient component, your application will most likely need to maintain some state information and require a timer to implement this type of algorithm:

• Start a timer.
• Send a message.
• Wait for an ACK from the recipient to return, or for the timer to timeout.
• If the ACK was received, send another message.
• If the timer timed out, resend the message.

Sending a Message with an HL7 Client

For detailed documentation about the methods and events for LlpClient, consult the documentation specific to your language: