We're attempting to network between an iphone and a computer (windows 7) using TCP/IP over Wifi. We are having a lot of difficulty setting up this basic network and we were hoping to get some guidance.
Server side:
Currently, we are trying to use MATLAB's tcpip protocol to set up the connection on the computer. We have determined the IP addresses of the phone and the computer and we picked a port number (501), that we are trying to read and write from. We allowed that port number in windows firewall.
In simulink we set up a TCP/IP send block to send out a constant, by double-clicking on that block and selecting the "verify address and port connectivity" button we get the error message:
"The remote address '140.180.....' has been found. However, we are unable to connect to the server at the specified port.
Specify a different port or wait for the current port to become available"
We have tried other port numbers, but gotten the same message.
We have tried using an ad hoc connection between the computer and the iphone to the same effect.
We have also tried other MATLAB scripts to set up the connection (e.g. http://www.mathworks.com/matlabcentral/fileexchange/24524) but we always get and error in the connection
Finally, we tried sending and receiving info over TCP/IP with the same computer using two MATLAB instances running in parallel, but we generally get the same error message.
We even tried UDP...no dice.
Client side (iphone)
We're using NSStream exactly as per this tutorial: http://www.devx.com/wireless/Article/43551/1954
The stream is opened upon a toggle action, and we immediately send a string to the server. We also tried sending a continuous sequence of data with the run loop. One strange bit of behavior is that, after the stream is open for a little while (~1 min), the handleEvent method does seem to get triggered (implying something is received from the server??) because we get a log message corresponding to case NSStreamEventErrorOccurred.
We think the issue lies on the server side, but really don't know enough to be sure or to debug properly. Any help would be very much appreciated.
A long overdue answer to this one: don't network with Windows. We eventually thought to switch over to a mac and lo and behold everything worked properly.
Related
I have been trying to make this standalone matlab code that uses the TCP networking commands given by matlab. When I debug the code in the matlab enviornment it connects right away, but when I run it as a stand alone it takes forever to connect or does not connect at all. It basically becomes very unreliable during the connection set up. Once the connection is set up data is sent and received quickly without issue. Does anyone know why this is happening or have a way to fix this?
I'm having some trouble with this, and have a hard time explaining the problem in words, but I will do the best I can.
I would like to send a simple message to a computer from a different computer. Nothing fancy. I have done some research, and a lot of sources say to create a script that accesses the built-in MSG.EXE function in Windows (I am currently on Windows 10) however, this only seems to work on machines connected to LAN.
From what I have gathered, I would need to create a website that handles the requests: get message from Computer A and send it to Computer B. Could I do this (In Powershell or VBS) without having to make a site specifically for it?
What I want:
I want Computer A to send a plain-text message to Computer B. Preferably, when the message is successfully sent a message box will appear that says "From: (whomever) and the message. Using MSG.EXE did what I wanted it to do, however it only worked with LAN-connected devices. Could I make this work with static IP? If so, how?
Additional Information:
The two computers are not on a LAN, but are connected to the Internet.
Computer A (the sender) and Computer B (the receiver) each have a static IP address, however that can obviously change.
Ports are available in each computer.
I have a Raspberry Pi that could act as a server "middle man" should that be required.
To be very clear: There are a lot of posts that talk about sending messages over LAN. I am NOT trying to send a message over LAN. Any help would be appreciated.
You're being quite vague in why you want it and what you want it to do; the main problem is that home internet connections are built for things to connect out, and nothing to connect in.
Fixes:
Port forwarding where you say "incoming connections go to this or that computer.
Building a service where both sides "connect out", i.e. you have a website hosted somewhere out on the internet. One computer connects out to send the message, the other connects out to check for messages.
Outside that, the next problem is knowing where on the internet to connect to.
Fixes:
Hard code the end points. Static IPs are good for this because the definition of a static IP is that it's an address which doesn't change. Mysteriously, you have static IPs which can change and you consider that 'obvious'. (??)
DNS where you register a domain, and the computers look at a domain name for where to connect. You update DNS with the current IP.
DNS where you use a free DNS service on someone else's name and your service listener updates that as its IP changes.
And after that, most people's computers/laptops/phones are switched off or in low power sleep mode most of the time, and their internet connections are comparatively unreliable, so any random message probably won't be answered.
Fixes:
Use a serious website service
Run an always-on computer to be that service
Deal with it being offline and messages being flakey
Use a store-and-forward system like email, which queues and retries, like e-mail and instant messengers do
get message from Computer A and send it to Computer B. Could I do this (In Powershell or VBS) without having to make a site specifically for it?
Yes. Quick answer: pick a port, configure site B's modem/router to forward the port to computer B. Open the port on computer B's firewall. Write some kind of TCP socket listener on Computer B, and the sender on Computer A, connecting to the public IP address of site B.
Long answer: then enjoy writing your own messaging protocol, error handling, message authentication, etc.
Alternative: do the same but going to your rPi. Have it listening. Not in powershell (sadly) or vbscript (luckily), and have it serve the messages up by HTTP/JSON, both computers invoke-webrequest or invoke-restmethod and post/get them with regular polling.
I have written one client socket program using linux sockets only. Here is the information giving picture what I am doing in my program
Creating the socket
Making connection with server socket
assigning that socket to read set and exception set for select.
using the select method giving the timeout value NULL in a separate thread
Server is running in one external device.
this program is working fine for reading and all.. Now I am facing problem when I unplug the power cable of that device.
I assumed that when we remove the power cable of the device all the sockets will abruptly closed and connected client sockets will get read event. when we try to read we receive number of bytes read as zero that means connection closed by server.
But in my program when I unplug the power cable of the device, Here in my client program select is not coming out means client socket is not getting any event. I don't understand why..
Any suggestion will be appreciated on how we can come to know that connection is closed by server or any information on whats the sockets behaviour when shutting down the power supply.
I need your help, its very critical.
thank you.
When a remote machine is suddenly cut off the network (network cable unplug or power loss), there is no way it can inform the other side of the connection about that. What is more the client side that performs only reads from a half-open socket (like in your case) won't be able to detect this either.
The only way to know about a connection loss is to to send a packet. Since all data being sent should be acknowledged by the other side, TCP on a client computer will keep retrying to send an unconfirmed portion of data till the number of attempts is exhausted. Then a ETIMEDOUT error should be returned (via a socket that is expecting read events). You can create one more socket for sending these messages periodically to detect a peer disappearance (heart beat connection) on the client side. But all this retries might still take some time.
Another option could be to use SO_KEEPALIVE socket option. After some time a connection has been idle, TCP starts sending probe messages to the server and can detect its disappearance. The default values for idle item are usually enormously huge, so they need to be modified. Some of other parameters that might be related (TCP_KEEPCNT, TCP_KEEPINTVL, TCP_KEEPIDLE). It appears, this option might be implemented differently on different systems or can be simply absent.
I've never personally tried to solve this problem so all this is just a bunch of thoughts that might give some ideas. Here is one more source of ideas.
I have setup a TCP/IP client/server connection that will open and close the connection every time a request is exchaged. It works perfectly; the client app opens the connection, sends the request and waits. The server application receives the request produces a response and sends it back and closes the connection. Cient and server apps do that hundreds of times.
Now I was trying to go to the next step: setup the source IP address and port.
The code was supposed to work on both Linux and Windows, so SO_BINDTODEVICE is out of question, since it is only supported on Linux/Unix.
I tried to bind the source port and ANYADRR on the client socket. And it works... For a while. Eventually it thorws error 10038. I've read over the internet several articles but without clear answer... The selection of the source IP remains unclear.
Please, note that I also have a UNICAST and MULTICAST mode on the same library (connectionless UDP communication modes), a sender and receiver, and I was able to setup the source port/IP on the MULTICAST mode, UNICAST I didn't try yet.
Anyway, anyone know anything that could be of help? I'm using WinSock 2.2 and trying to be as much as possible platform indemendent.
Winsock error 10038 is WSAENOTSOCK, which means you have a bug in your code somewhere. You are trying to do something with a SOCKET handle that is not pointing at a valid socket object. That has nothing to do with the bind() function itself. Either you are calling socket() and not checking its result for an error, or you are trying to use a SOCKET handle that has already been closed by your app, or you have a memory overflow somewhere that is corrupting your SOCKET handle.
I am creating a class which communicates with remote server. Currently my device (iPhone 4) is having connectivity via wifi and local network cellular. By default it uses wifi. It works fine in both the cases.
However when I switch from wifi to cell service, it hits error delegate. I want keep communication on going even when connectivity is changed.
Is it possible? How?
Thanks,
I don't expect it is possible. Having switched networks, you've probably also switched IP addresses. Connections are defined by the IP addresses of the end points (as well as protocol and protocol-specific data such as port numbers). So, you can't maintain a connection when the IP address changes. You must cleanup and dispose of the broken connection and open a new one.
If the high-level protocol you're using, such as FTP or HTTP, allows it, you can try resuming the data transfer at the point it was interrupted. For example, if downloading a file, you may be able to resume the download at the file position of the last data you received.