IP Communication
190
NetLinx Programming Language Reference Guide
 LocalPort: A user-defined, non-zero integer value representing the virtual port on the client
machine that will be used for this conversation. This port number must be passed to
IP_CLIENT_CLOSE to close the conversation.
 ServerAddress: A string containing either the IP address (in dotted-quad-notation) or the
domain name of the server to connect to.
 ServerPort: The port number on the server that identifies the program or service the client is
requesting.
 Protocol: The transport protocol to use (1 = TCP, 2 = UDP). If this parameter is not specified,
TCP (1) is assumed. The constants
IP_TCP and IP_UDP can be used to specify this
parameter.
Terminating a conversation
To terminate a conversation, you must use the IP_CLIENT_CLOSE command and pass the number of
the local port used for the conversation. The syntax:
IP_Client_Close(LocalPort)
Parameters:
 LocalPort: A user-defined, non-zero integer value representing the virtual port on the client
machine that will be used for this conversation.
Sending data
To send data to the server, use the SEND_STRING command.
SEND_STRING 0:LocalPort:0, '<string>'
The device specification (0:LocalPort:0) is interpreted as follows:
 Device Number: 0: The master
 Port: LocalPort: The local port number
 System: 0: This system (the client)
Receiving data
To receive data from the server, use a DATA event handler or a buffer created with CREATE_BUFFER or
CREATE_MULTI_BUFFER. If an event handler is used, the data is located in the Text field of the DATA
object. The syntax is shown below:
Data_Event[Device]
{
STRING:
{
// process incoming string (Data.Text)
}
}
Parameters:
 Device is (or contains as part of an array) the device representing the conversation
(0:LocalPort:0)
When using IP sockets in NetLinx, it is not uncommon to create a buffer using a
CREATE_BUFFER
keyword and processing the buffer in the
DATA_EVENT...OFFLINE event.
Netlinx has an important behavior than can affect the performance of IP socket code. This is not a bug
but a feature. If you are aware of it, you can write your code to take maximum advantage of the speed
NetLinx offers.
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