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Name: Transport.lvlib Submitter: ShaunR Submitted: 27 Aug 2011 Category: Remote Control, Monitoring and the Internet LabVIEW Version: 2009License Type: Other (included with download) Transport.lvlib is a LabView API to simplify and accelerate networked communication development. It simplifies development by abstracting TCPIP, UDP and Bluetooth and TLS interfaces into a single polymorphic vi which is a thin wrapper around the conventional open, read, write, close and listener VIs for all the network interfaces. Features: Supports TCP/IP, Bluetooth, UDP (p2p, broadcast and multicast) and TLS. Supports symetric encryption (blowfish). Supports compression (zlib). INSTALLATION: Run the supplied installer and follow the instructions. Click here to download this file

I am running into an issue where my VI Server connection goes stale after a few hours. Looking for a fast way to detect this and recover. Currently here is what I am doing: On first call, open the application reference and then open the VI reference. Cache both of these. Use the VI reference to call the remote VI. On subsequent calls, test the cached references to verify they are still valid and then call the remote VI. What appears to be happening is the references still appear to be valid in the caller but the connection is broken so the remote call fails. Then I detect this and reopen the app and VI refs and can again call the remote VI. The issues are: The failing remote call takes a long time to timeout and I do not see how to control this timeout. The test of the refs does not actually test to see of the network connection is still good. The result is it takes a long time to recover and this is upsetting the user since it appears the system is locked up. What I need is a way to control the timeout of the 'call by reference' node or a way to quickly test the references to verify the network connection is still good before I attempt the remote call. Any ideas? thanks, -John

Attached is my VI for writing a tiny HTML file to a intranet network directory. This is on Windows for writing to a file path like \\foo\bar\wtf.html (fictional!). But when the network is slow (quite often) the file write will fail. I've got a patch in there so survive the error and just wait till next time. But what really I need is a way to tell the write to hang in there longer and not give up just because there's no reply yet. My temporary work-around is to open a Windows file browser to that path, the twiddle my thumbs until the file list populates. Then, the path being established, I may safely start the parent VI of which this VI is a sub. Any ideas? Write_HTML.vi

Hi, I'm wondering whether there is a way to monitor the SVE (or single processes/variables) on a per-client basis. The purpose of this would be network diagnostics or access control. I know the DSC module allows logging of data and events for shared variables, such as the very handy "value changed" event, but they contain no client-related information (to my knowledge), such as the client name or IP address. Are there any other shared variable events besides the value changed notification (e.g. "variable accessed"), which I have missed? Anyway, the SVE seems to be aware of clients, because it allows some access control through the DSC module (and with a bit of hacking even programmatically). You can define access control lists based on computer name or IP address, which is very buggy, but it works somewhat. Is it possible to somehow access this client information (number of clients, names/addresses and activities) from the SVE? I don't see any tools for that, but maybe there is an underlying API through DLL calls or whatever?

I need to find a transport for message objects that allows two way communication without polling but is limited to server side connections only. So, the client can connect to the server but the server cannot connect to the client. First some context: My application communicates over the network using VI Server. My client app (the UI) opens a ref to a VI in my server app (the engine) and sends a message object containing the client app’s machine name and VI server port. The server app then opens a ref to a VI in my client and sends a message object with the reply data. I now have a two way communication channel via VI server and can pass any message object back and forth without polling. I learned today that our IT department plans to block all incoming connections to all non-server machines in the future. So, my client would still be able to connect to the server app within the network, but the server would not be able to connect to the client app because of this rule. This will completely break my networked messaging system. I do not know a way for LabVIEW to setup VI Server so only one end can connect to the other but allow two way communication without polling. Does anyone use a message system that would work in my situation? I would prefer to continue to use VI Server but I am willing to look at other solutions, as long as they were very robust and had low latency. thanks in advance for you help. -John

Has anyone used LapDog to pass messages across a network? In my case I'm thinking of an RT system controlled from a Windows computer. The only similar feature I've seen is in the Asynchronous Message Communication Reference Library - has anyone already added something like that to LapDog? I just didn't want to spend too much time developing something that's already available. I haven't used either AMC or LapDog extensively before, but my impression is that LapDog gives a little more control and flexibility. (And the Actor framework perhaps a little too much, as a poor reason for not going that route!).

I have been working on an architecture that uses VI Server to send messages between application instances, both local and across the network. One of the problems I have run into is the fact that VI Server calls are blocked by activity in the root loop (sometimes referred to as the UI Thread). There are several things that can cause this: other VI server calls, system dialogs (calls to the one and two button dialog functions), if the user drops down a menu but does not make a selection... (I'm sure there are more...) Since this is a pretty normal way of communicating between applications, I was wondering if anyone had any ideas for a work around. Here is a basic description of my architecture: Message is created and sent to local VI that sends to outside application instance. Local sending VI opens VI server connection to remote instance. It then calls a VI in the remote instance that takes the message as input. This remote VI them places the message in the appropriate queue on the remote instance so it gets handled. If the remote instance root loop is blocked, the sending VI on the local machine is also blocked. I could try to eliminate all system dialogs from the remote application, but that only partially addresses the issue. I really wish a future version of LabVIEW would eliminate this problem with the root loop and VI Server all together. BTW: using LV2012 but this issue exists in all versions. -John

I am designing a method for multiple application instances to coordinate an action across a network. I have previously implemented this using queues for coordination of asynchronous VIs within a single application instance. I now need to make this work across a local network. I have been looking at network shared variables, network streams, TCP/IP, UDP. I would like to know if anyone else has accomplished this and what you learned along the way. The basic requirements are: N number of independent applications need to coordinate some action (essentially a rendezvous). No one application knows if the others exist. (don't know their IP or anything about them) No one application knows if it will be the first to join or will join later. All applications will share a common name for the rendezvous. The first application should create the rendezvous As other join, they should see that the rendezvous already exists and join it instead of creating a new one. All applications should be able to see how many have joined. When all applications depart, the rendezvous should be destroyed by the last one to leave. Thanks for any tips or examples you can share. -John

Hi everyone, I'm wanting to open up the floor for your opinions and past experiences with designing a network communications architecture. - There will be one server, written in LabVIEW on a Windows based PC. - There will be multiple remote clients programmed in LabVIEW on cRIOs. - All devices will be connected via a wireless network, and all cRIO clients should have good throughput to the server. - It should be designed for bidirectional data flow, however the clients will do most of the talking. - Data sent will be, status packets, images, PDF documents, and other information. - Clients will not be continuously sending data, such as a typical DAQ system, but more reporting on events. I'm leaning towards the TCP socket option, but would like to consider higher-level forms of NI-propriety designs, such as Network Shared Variables or Network Streams, which I haven't had huge amounts of exposure to. Thanks for your opinions. Brenton

Hello everyone, My project: We have 2 PXI-RT communicated by 2 connections: a fiber optics connection (not Ethernet), and an Ethernet connection. The FO connection is the main connection used to wsend a receive data. The Ethernet connection is only use when the FO connection is lost, in order to check if the "mute PXI" has lost the FO connection but is still on, or if the PXI has been switched off. The problem: Originally we used the "RT Ping controllers.vi" on the "Real-Time Utilities", but unluckily we changed the PXI controller and the new one is not supported by the library. The main issue is the application was developed using LV7.1 and cannot be upgraded. Options already disscarted: We tried opening a TCP connection, but the operation takes too long. I found this great VI, but its for LV2010. I tried it and it works perfectly. (http://forums.ni.com...er/td-p/1535420) I tried translating it to LV7.1, but something is wrong, because LV closes as soon as I play Run Have any of you worked using wsock32.dll on a PXI? Best regards, g_l_u_p ping_PharLap_LV711.vi