On Sat, 02 Jan 2010 16:20:44 -0800, David Nebenzahl
put finger to keyboard and composed:

I know it can be done, but am having trouble making it work.

The idea is to connect 2 PCs directly through their modems. Not cable
modems, ordinary 56K modems. I call it my "Poor Man's Network".

I've found the following pages that describe this operation:

http://phorums.com.au/archive/index.php/t-120530.html
http://www.jagshouse.com/modem.html

That second link suggests powering the connecting line with ~24 VDC, but
I don't think that's actually necessary. (The first link describes
connecting two computeri via modem with no extra hardware needed.)

So when I set this up--2 computeri with connected modems, using
HyperTerminal at each end, with the following commands:

o sending computer: ATX3D
o receiving computer: ATA

I hear stuff through the speaker on the RX end, typical modem connect
tones to start, but I don't hear all that "chirping" usually associated
with dial-up connections; just a steady, low tone that lasts for, say,
30 seconds or so, then the connection goes dead and I get "NO CARRIER"
at both ends.

Everything seems configured correctly: I've set the speed at both ends
to 56K and disabled waiting for dial tone.

So what am I doing wrong here?

Some modems have a transformer based DAA and electromechanical relay,
others have a silicon DAA. The latter consists of a host side chip and
a line side chip. The line side chip requires loop current to operate.

You can tell whether you have an DAA with a electromechanical relay by
muting the modem's speaker and commanding it to pulse dial (while
disconnected from the phone line).

ATL0M0DP00000000 (all zeros, no "ohs")

Listen for the clicking of relay contacts.

- Franc Zabkar
--
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