How can a VI be both server and client?

Question

Hi, 
I'm new in LabView and I'm trying to build a server and client VI using TCP/IP that runs in two computers. in my program I need both server and client VIs to communicate with each other which means I need both VIs to be server and client. I've tried using a case structure but it doesnt work. The only thing I achieved is a normal server/client system where the server sends a request and the client responses.But i need the client to send requests too.i have attached my VIs to this post.I would appriciate it if someone could help with this problem. 
Thanks in advanced. 
Rambaldi.
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Server-Client.zip ‏41 KB

Answer 1

Do you really need a client and server on each PC? If you simply need that two to talk to each other they can once the client connects to the server. In most cases you only need one server.
What Steve said about the not using the same port only applies to two servers on the same machine. A client must use the port the server is listening to and if the client and the server are on the same machine then they will both use the same port. However, only ONE of them is accepting waiting for connections on that port.
In the code you posted you actually swapped the names. What you call the client is actually the server code and vise versa. In networking a server is an application that listens to an assigned port, accepts connections on that port and provides whatever services it has implemented. A client is an application that establishs a connection to a server. Once a connection is established the two applications can communicate in both directions. The applications themselves will define how the conversation should progress and whether it is a one way conversation or a two way conversation. You don't specify what you are trying to accomplish but I suspect you only need a single server.
In TCP, every connection is defined by the source and destination IP addresses and the source and destination ports. The server uses a known port (FTP is port 21, HTTP is 80, telnet is 23, or some custom port in the user space beyonds the reserved ports) to listen for connections. The client will use the well known port of teh server and generally picks a random port for its port number. The LabVIEW VIs do this automatically. This is how a server and a client on the same computer can use the same port number. Two servers however cannot. The server application can spawn a child task allowing it to service multiple connections at one time though. Each connection will be unique though since the client's port number, address or both will change for each connection.
OK, end of networking 101.
Can you describe in a bit more detail what exactly you want to accomplish. Given that I could probably provide you with more information for your application.
Mark Yedinak
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