Our project is LIDAR which is based on physics. The total equipment is connected to server which consists of various sensors. Server gives total information about the equipment like temperature, humidity etc. Server and laptop are connected through LAN. Our work is to develop a software using labview which interfaces the equipment with the laptop. To achieve that first we have to connect the server to the laptop. We have tried in so many ways using TCP/IP vi in labview. Both server and client programs are required to do this. In the server program we are using TCP Listen and in the client program we are using TCP open connection. Which IP address and port address should be given to TCP listen and TCP open coonection ?
The IP address and port should refer to the server as shown in this snippet (replace port with your chosen port and localhost with your server address):
The example code I have shown above has two code blocks, the TCP Server should run on your server and the TCP Client should run on your laptop. The remote address would then need to be changed to the address of your server. Using the above example only shows how the connection is made and a single item of data transferred before closing the connection. You would need to wrap up some extra code to provide any handshaking between the server and laptop to provide the required functionality in your application.
In LabVIEW you will find some examples on how to use the TCP function, from the top menu select 'Help' and 'Find Examples...' then using the 'Search' tab type in TCP and you will see 'Simple TCP.lvproj' that should give you something that will get you going.
If your project doesn't specifically require you to use the TCP listen/open VIs then you might want to consider some of the built in networking functionality that comes with LabVIEW.
I've had good luck with LabVIEW's network shared variables stuff where you can, among other things, connect a front panel control on the client to a variable shared by the server, and LabVIEW takes care of all of the TCP functions behind the scenes.
Here's one webpage about the feature:
http://zone.ni.com/reference/en-XX/help/371361G-01/lvconcepts/ni_psp/
Related
I'm receiving lots of information per client, and i don't know how to handle it. If i make lots of connections to one port will it work? Now, I'm using 1000 ports open with only one client. Do I change?
Typically, one application or one major part of application should have its own port. For each client that connects to the port, you spawn a process/create a thread to service it. After the service is complete and the reply sent back, if connection is not persistent, you close it.
After all, you can only have 65535 ports open on your pc (theoretically), and not all of those are available for private (non system) applications either.
So the way to go is to have one port for application/major application functionality. E.g.
Database Management Systems (e.g. DB2) can have a (theoretical) max limit of 64000 connections per port.
http://pic.dhe.ibm.com/infocenter/pim/v6r0m0/index.jsp?topic=%2Fcom.ibm.wpc.adm.doc%2Fdata_admin%2Fwpc_con_managedb2connections.html
Multiple clients can connect to the same listening port, so you only need to open 1 port in most cases (some protocols, like ftp, use multiple ports). It is the combination of client IP/port and server IP/port that uniquely identifies a connection, so it works just fine. There are multiple programming models available to allow a server to service multiple clients at one time.
I am working on a program related to network, and there's a situation that the client has to connect to a server which is inside a LAN.
As I know, when establishing a TCP connection, the port the server is listening on has to be accessable to the client. If the server is inside a LAN, port accesses are blocked by the router. One solution I know is to use UPnP to perform a port mapping on the router. However, in some cases, the router does not support UPnP, are there other solutions?
IM applications came up into my mind. Many IM applications have the functionality that users can send files to each other, whatever the network environment is, as long as you can access to the internet. I don't think a public server is used as a file data exchanger between the two, the connection has to be a direct one. How do they actually do to enable the client to connect to a "hidden" server?
Typically such programs try a series of steps:
A connect directly to B
B connect directly to A
A tries to connect to a firewall (uPnP) forwarded port to B
B tries to connect to a firewall (uPnP) forwarded port to A
A and B both connect to a central server and exchange data through that
The last step is obviously the least preferred because the provider has to have sufficient resources to manage all simultaneous transfers. Rate-limiting is common.
Since IM has central management anyway, it's not too difficult to coordinate all this.
If uPnP or an open port can't be done at one end or the other then the only option left would seem to be passing it via a server in the middle
I found a tutorial that shows you how to create server and client programs, and make them communicate over a network.
http://www.win32developer.com/tutorial/winsock/winsock_tutorial_1.shtm
I can make a client program connect to, for example, 192.168.0.4 on my local network, and I can make it connect to 74.125.225.96. But what if I wanted to make it communicate with 192.168.0.4 on the network of 74.125.225.96, instead of just the default server on 74.125.225.96? I'm having a difficult time finding the answer with Google.
Is there even a way to do this? If not, then how are Gnutella and Bittorrent, able to connect computers directly together to share files?
To do what you are asking, 74.125.225.96 would have to be assigned to a router that is configured to forward inbound connections on the target server port to the machine that is running 192.168.0.4.
BitTorrent and other file sharing apps use various techniques, like NAT traversal, hole punching, etc to get connections through routers and firewalls. For example, if one party is behind a router/firewall and the other party is not, then the two apps first try to connect to each other in one direction, and if that fails then they reverse roles - client becomes server and server becomes client - and they try again. If that still fails, they could then connect to a middleman server that both parties have access to, and let it delegate the connections.
Some background first. I have a .net client agent installed on each of the machines in the lan. They are interacting with my central server [website] also on the same lan.
It is important for my website to figure out which of the machines can talk to each other. For example, machines of one subnet cannot directly talk to machines of another subnet without configuring the routers and such. But machines in the same subnet should be able to talk to each other directly.
The problem I am facing is when the lan setup is like in Figure 1.
Because Comp1, Comp2 and Comp3 are behind a router, they have got the ipaddress 192.168.1.2 till 192.168.1.4. My client agent on these machines report the same ipaddress back to the server. However, machines Comp4, Comp5 also have the same ipaddresses.
Thus, as far as my server is concerned, there are 2 machines with the same ipaddress. Not just that, because the subnet mask is 255.255.255.0 for all machines, my server is fooled into thinking that Comp1 can directly talk to Comp5, which is not possible.
So, how do I solve this? What do I need to change in my client or in my server, so that I can support this scenario. These two are the only things in my control.
EDIT: Seems that the network diagram
is over simplified and there could be
multiple router/subnet levels. My
original answer will not handle this
scenario. Also, with the restriction
of modifying only the client app or server
app and not tampering with the
routers and firewalls makes
it more difficult.
EDIT2: Using 'arp -a' you can extract
the MAC address of the router. If the
client apps can manage to do this then
the puzzle is solved!
The client app knows the local machine address and passes it to the server app.
The server app knows the remote address when a connection comes in. This would be machine address or a router address.
From these two values you can work out what you ask.
For example:
Server app receives connection from 10.10.10.2 with client supplying 192.168.1.2
Server app receives connection from 10.10.10.3 with client supplying 192.168.1.3
The 'remote address' distinguishes the subnets.
So, all you need to figure out is how to extract the remote address of a client connection. If you are using any of the popular web technologies for your server app then this is very easy.
One approach is for the individual client machines to determine who they can see using a broadcast message. Have each client listen on some particular UDP port, and each client broadcast its presence to whatever the local broadcast domain is. When clients can see each other in this way, they can probably also make TCP connections to each other.
If the server needs to know which clients can talk to each other, just have the clients tell the server.
If the network diagram is complicated enough I think if would be very difficuilt to find what you need.
You should also take into account that Comp1 can establish direct connection to Comp6.
The solution I can suggest is probing. Client receives list of all other clients from server and tries to establish connection to each of them. I think that would be the only way to know which clients are REALLY accessible assuming any number of routers/firewalls/NATs in the network. Doesn'r scale much for a big number of computers of course.
In short: How to reliably discover a server running somewhere on a (presumably multi-segmented) local area network with zero client configuration
My client application has to locate the server application without knowing the server IP address. It has to work on a local LAN that may be split into segments with hubs or other switching devices.
I already have a working solution, but it is a bit cumbersome to get it working on multi-segment networks. It works as follows:
When the client starts up, it sends UDP broadcasts on its own network segment. If the server is running on the same segment, it works without any issues - the server responds with the appropriate messages.
If the server and client are running on networks separated by a hub / switch that won't forward UDP (the most likely case), then I have a server instance running on each segment, and they forward client requests to each other via TCP - but I need to configure this for the server instances (simple, but still a pain for tech support.) This is the main problem that I need to address. There are sites where we have hundreds of clients running on 5 or 6 separate segments.
The problems I'm facing:
1. Although my application installer enables the appropriate ports on the firewall, sometimes I come across situations where this doesn't seem to happen correctly.
2. Having to run multiple server instances (and therefore configure and maintain them) on hub/switched networks that won't forward UDP
Finally I need a solution that will work without maintenance on a minimal Windows network (XP / 2000 / Vista) that probably doesn't have Active Directory or other lookup services configured.
I don't want to tag on any runtime stuff for this - should be able to do it with plain VC++ or Delphi.
What approaches do commercial apps usually take? I know that SQL Server uses a combination of broadcast and NetBEUI calls (I may be wrong about this).
Thanks in advance.
You have a few terminology issues:
Where you say "network segment" you appear to mean "IP subnet". Devices on the same network segment can see the same IP broadcasts.
Where you say "hub/switch" you appear mean "IP router".
Where you say "won't forward UDP", the problem is actually "won't forward IP broadcasts".
Once we get past that, you have a few options:
Your servers could register themselves under a well-known name in DNS, if you have a DNS server that allows dynamic DNS updates. You should probably use a SRV record as specified in RFC2782. The clients then do a DNS lookup to find the server(s).
You could statically assign your server(s) well-known names in the organisation's DNS, perhaps with a SRV record as with the previous option.
Your servers could join an IP multicast group, if your routers support IP multicast. The clients then send their initial discovery request as a UDP packet to the (pre-ordained) multicast address.
If you have domain server, I would go with small service on it. You can connect with other services to it and use it as distribution point.
Why domain server? It is relatively easy to find it's name (DsGetDcName).
Other choices would include DHCP server, DNS server or something of that kind that needs to be filled by maintenance staff anyhow.