[PLUG] LAN broadcast?

Wayne E. Van Loon Sr. wevl at pacifier.com
Wed Jun 1 23:04:13 PDT 2011

Hello Tim:
Tim wrote:
> Hi Wayne,
>> I have a question about user applications using broadcast on a LAN.
>> I usually have several processes that connect via TCP/IP to a central 
>> server that solves some optimization problems. In more demanding project 
>> that I am working on now, I hope to distribute the optimization problem 
>> between 24 to 36 helper processes.
>> At the start of each optimization job, I will have a few data files that 
>> need to be distributed to each of the helper optimization processes. 
>> Rather than have the central optimizer / server send these files 24 
>> times, some way to broadcast these files to all machines / processes at 
>> the same time might be nice.
>> Is that the kind of thing that broadcasting could accomplish?
>> And if so, and in a big picture way, how would one do it?
> You could use broadcast, yes.  Most likely you would want to use UDP
> for this, since TCP handshakes and broadcast doesn't really mix.  To
> accomplish this, you would simply have each helper process listen for
> the broadcast messages and then send results back to the central
> server at the server's unicast address.  
> However, a "sexier" way of accomplishing the same thing would be to
> use multicast.  This would allow you to distribute the broadcast
> messages scalably across router boundaries.  Multicast is really
> powerful for specific applications like this and I hope it catches on
> some day, since it can completely replace distribution models like
> bittorrent.
> Finally, instead of implementing all of this distributed
> computation/communication yourself, you might consider using an MPI
> library or even building a BOINC application.  Or maybe you don't need
> to go distributed at all for the scale of your project by instead
> leveraging the massively parallel processor you probably have in your
> system (a.k.a. your video card).  See OpenCL.
> HTH,
> tim
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Not surprised. I couldn't see a way to broadcast using SOCK_STREAM. 
Googled all over trying to find an example. Does it follow that since I 
would like to use SOCK_STREAM for the rest of the communications during 
the optimization job, the multicast side would need to be on a second 
network interface?



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