TCP/IP broadcast how to ? from a greenhorn

[willowLAR]

Hi,
Networking is not my expertise but I've put all of my instruments and computers onto a LAN. Ideally, I would like to collect the same data from one instrument on two computers. I have been trying to understand broadcasting and have yet to. If anyone can provide any assistance or point me in a helpful direction, I would be very thankful.

Specifically I have a serial to ethernet converter (startech.com) that is transmitting data successfully to one computer. In order to recieve the data on another computer do I need new hardware or software? Or is it simply a matter of IP addressing? If I need new hardware or software, can you recommend anything?

This networking greenhorn thanks you very much for your time.

Sincerely,
Willow Foster

Research Technition
Laboratory for Atmospheric Research
Pullman, WA

 

[pansophic]

What you are looking to do is called multi-casting, not broadcasting. Broadcasting is listened to and heard by all devices on a subnet. Multi-casting is listened to by every device that has registered to see that particular data. Unfortunately, I doubt that your serial device can register as a multi-cast server.

The first thing that I would look at would be the ability to telnet to the device with two computer simultaneously. If two connections can be simultaneously attached, then you really don't have any other issues. If not, then you would be looking for a software-based solution. One obvious choice would be a PERL script using Net::RawIP, but you would need to look into the protocol used to interface with the serial device (it may simply be telnet).

Ethereal is your friend here.


pansophic

 

[edfair]

Does your software give the option of direct connect to the data provider via serial cable? If so, one possibility would be to convert from IP to serial and input into the 2nd computer via a serial port.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[willowLAR]

Thanks for the suggestions. No, I cannot telnet from two computers simulateously. I can have the startech serial to ethernet converter set up the port as a "virtual" serial port, but it still won't let me connect with two computers. I'm thinking that maybe I can grab the data with one computer and then resend it to the other. Not sure exactly how that will work. I'm also looking into software such as pansophic suggests. I'm not familiar with PERL, but maybe their is another language/program I can use. We use LabView a lot around here. Any chance someone knows how to do the same with LabView?

Thanks for you help, it is helping.

- Willow

 

[jneiberger]

As Pansophic said, multicasting is probably your best choice. However, if you don't have a lot of devices on your LAN (or if the traffic volume on your application isn't very high) then broadcasting might work just fine. Set the destination IP address to a.b.c.255, assuming that you're using a /24 subnet mask.

One other issue you may have is that the destination might respond differently to broadcasts than it does for unicast packets, so it may stop working as you intend. You'll have to do some testing to see how it behaves.

 

[pansophic]

LabView is great for processing the data that is received, but as far as I know, it will not perform packet copying functionality.

Do you need the data to go to both systems simultaneously, or could you capture on one system that is collecting real-time, and use a file containing the data to process on the other system? If so, WinDump will allow you to capture the raw packets before they are processed. Using some simple filtering or using Ethereal manually you can parse out the data payload from the packets and feed that data file to the other system.


pansophic

 

[willowLAR]

Thanks pansophic. I'm gonna look into WinDump. Ideally the data is recieved simulataneously, however if there is a known delay, that can be accounted for. I'll let you know how it goes.

- Willow

 

[pansophic]

WinDump date and time stamps the packets as they come in. I haven't used it in years, but you used to be able to use an application called TCP Replay (*nix) to play the packets back out onto the network with the same timing, or at full rate. With a little creativity you could theoretically change the destination IP address in the WinDump capture file and replay it to the other machine.


pansophic