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Re: Serial Connection -- shielding

Le 30/03/11 03:27, Stephen Powell a écrit :
On Tue, 29 Mar 2011 10:18:50 -0400 (EDT), MAROUNI Abbass wrote:
I think that the discussion diverted somehow from my original question.

My problem was  the following :
Two identical servers Z0&  Z1 and a null modem cable. ttyS0 on Z0
connected to ttyS1 on Z1.
on ttyS0 on Z0 I have a getty listening for incoming connections.
on ttyS1 on Z1 I launch a minicom toward ttyS0 on Z0 and I login normally.

Now When I try to do the inverse :
Kill getty on ttyS0 on Z0 and remove it from inittab. Set getty to
listen to ttyS1 on Z1. Launch minicom on ttyS0 on Z0 toward ttyS1 on Z1.

I can't login all I see is garbage.  All the serial parameters are the
same on both sides.
I thought that logically this setup have to work since I am using the
same setup just changing which port on which server.

I am trying to do this for a Datacenter with hundreds of servers. This
way I can connect two servers together with just one serial cable.

Does it have something to do with the ttyS0 port? is it a software problem?

Do you have any ideas ? (Apart from theoretical discussions about all
the standards)
As I've said before, the devil is in the details.  You need to find out
*exactly* how your cross-over cable or null modem is wired.  There may
be some asymmetry in the wiring that causes the cable to behave differently
in opposite directions.  The wiring should be symmetrical, ideally as
shown in the following URL:


The other possibility is that the serial communications settings
are different.  For example, minicom (or getty) might not be
configured exactly the same on both servers.  (Data bits, stop bits,
parity, bit rate, type of flow control, etc.)

It really is much
easier with two serial ports per server and two serial cables.
Connect /dev/ttyS0 on server 1 to /dev/ttyS1 on server 2 and
connect /dev/ttyS0 on server 2 to /dev/ttyS1 on server 1.  Have
getty listen on /dev/ttyS0 on both servers.  Have minicom open
/dev/ttyS1 on both servers.  I realize its two cables instead
of one, but operationally it's much simpler.  You want to do it
with one cable?  How about TCP/IP over ethernet and ssh sessions?
That way, you can connect to any PC in the network with just one
cable per server.

The Two servers are exactly the same. getty and minicom have the same exact parameters. We need to use the serial connections in case one server is unaccessible or haven't come up after a restart, so we can connect to its pair and pass through the serial connection to see what's happening. The idea of using a single cable is to enconomise. I thought it would be relativley simple since it's logically possible. I migth need to check the cables but I think it's the standard Null modem.

I thougth that it had something to do with port0 (ttyS0), but if the OS treats all the serial ports the same then it's not a software issue?


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