Re: Big knowledge gap wrt TCP/IP

From: Helmut Giese (hgiese_at_ratiosoft.com)
Date: 08/30/04 

Date: Mon, 30 Aug 2004 21:09:17 GMT

On Mon, 30 Aug 2004 18:52:23 GMT, hgiese@ratiosoft.com (Helmut Giese)
wrote:

>2) In each sub-net we will have a Linux box acting as a router (?) -
>that is, this machine will receive all packets / data which has to be
>delivered to a different sub-net. (A local expert will set up all
>machines on this network.)
>2a) If it makes any difference, the "local expert" mentioned today,
>that we could also configure this Linux box as a "bridge" ...
>
>My problem is (2). I suppose I will work with sockets, but there my
>knowledge ends:
>- Which extension could I use to receive (on the Linux box) the data
>which needs to be routed somewhere else?
>- Given that I get the data, how do I find out to which sub-net /
>target address it has to be sent to?
>- Probably more questions once I get started ...
>
>Should you need more information, I will gladly provide anything
>needed. However, given my ignorance in this matter, it would
>accelerate things, if - when asking for a specific piece of
>information - you could also tell me how to obtain it.

Sorry, I have to add an important piece of information (Heinz-Detlev's
advice made me aware of the omission): On the Linux box I cannot just
forward (via SLIP) whatever I recieve (via TCP/IP) - the connection
has to be explicitely established by some "master" which effectively
controls the power-line communication (as I mentioned, the setup is a
bit, well, non-standard).
This is the situation:
- We have an electrical 3 phase net.
- At each phase we have a power-line modem connected to a Linux box.
>From the POV of the power-line communication mechanism, these are
slaves.
- We have a master machine in the background, which will initiate any
communication. This is a Windows machine where we have to talk via
Microsoft's COM interface to a software the vendor of the power line
modems provided (BTW, this now works like a charm with the tcom
extension.)
- Now, although slave1 needs to talk to slave2, there is no way to
achieve this directly. Rather, the master will poll each slave in turn
and ask it, whether it has some data to transmit.
If so,
- it is then allowed to send it,
- the master closes the connection to slave1,
- opens the connection to slave2 (the actual destination) and
- eventually transmits the data to slave2.
Turning around as fast as possible, it is supposed to look to the
outside, as if slave1 could talk directly to slave2 - albeit not very
fast.

So, more precisely the requirements are:
- accept (and buffer) all TCP/IP packets which arrive,
- wait, until a serial connection is established by receiving a
"question" from the master (see above),
- and then SLIP everything I collected so far.

Also note, that the power-line communication is really sloooow, so
that we need to minimize any communication overhead.
Best regards
Helmut Giese

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