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Connecting 2 modems directly for gaming

Posted on 1998-04-18
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Last Modified: 2013-12-27
I would like to play multiplayer games over 2 PCs by directly connecting them together via their modems using a telephone wire. I have successfully transferred files using Bitware and the modem strings ATX0D on the dialling modem and ATA on the answering. However I have not been able to make the modems talk to each other within a game. I think the problem lies in the answering modem since I was able to make a connection when I dialled within the game on one machine and used Bitware on the other to answer.
I want to do this as I have a long telephone wire but no null-modem cable.
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Question by:rifraph
11 Comments
 
LVL 5

Expert Comment

by:JBURGHARDT
ID: 1146575
It will be easier for you if you buy two network cards and cable go to www.onsale.com/computers.htm
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Author Comment

by:rifraph
ID: 1146576
I don't want to go to the expense of buying additional hardware. I have read on the web somewhere that a 9V battery can be used to give the telephone wire a voltage potential (to simulate a live connection?), but am unable to find the page again.
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LVL 12

Expert Comment

by:alandc
ID: 1146577
It they're that close together wouldn't a null modem be a lot faster, easier AND more reliable?  I mean you can get a full 115kbps on a null modem connection!  The best you can hope for on faked out modems is about 34kbps.

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Author Comment

by:rifraph
ID: 1146578
Obviously, but they aren't close together and I don't have a null modem cable. How long can a null-modem cable be? My phone cord is about 25m but it has only 4 core wire.

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Expert Comment

by:hexar
ID: 1146579
Get a null modem cable.  I have one, to link my two computers,
and the one I have is only about 6 feet long but they are both
right next to each other.  This works great for Warcraft II and Doom 2 and Rise of the Triad.  I can transfer files at approximately 9 Kilobytes a second.  Unfortunately, places like Best Buy will not have them so you need to look in your Yellow Pages for a company that has one.  In fact, some of them might not even know by the term "null modem", so you might have to explain that the receive is connected to the transmit for both ends.  As opposed to serial cables which are TR/TR and RC/RC.

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LVL 84

Expert Comment

by:ozo
ID: 1146580
RS-232-C suggested a maximum of 50ft @9600baud on cable with a capacitance of 2500 pf/ft
but if you have 10pf/ft cable then 250 feet at 20 kbps would be reasonable.
With only 4 wires, you won't get hardware flow control, which may put more demands on your recieve buffer,
But if you can handle the protocol without hardware handshaking it might work

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LVL 3

Expert Comment

by:jlove1
ID: 1146581
I think you're only answer is to use a NULL MODEM CABLE. I use a null modem cable that's 50 foot long. I always choose 115200 for the speed and it works great.

I'll explain you're modem problem.

#1, the line voltage / Dial tone problem.  first, the dialing modem ALMOST ALWAYS needs a dial tone in order to pick up and dial. (this CAN be overcome using modem init strings.. check your modem documentation for details).

#2 The RECIEVING modem needs a "RING" before it'll know to pick up. I'm sorry, but there's no way to make one modem simulate a "ring". If I'm not mistaken, a ring is a rise in voltage from 9 volts to 12...

Sorry, but just TRY the Null Modem solution. It's VERY CHEAP...

Another way to do this is to MAKE your own null modem cable using telephone cable for the wires. You'll need the CABLE PINOUTS which can be found at
http://dco.cbi.tamucc.edu/guides/rj45-2.html

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Author Comment

by:rifraph
ID: 1146582
If the modems can talk to each other with a comms. package, doesn't that mean one modem is already capable of answering?
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LVL 3

Accepted Solution

by:
jlove1 earned 200 total points
ID: 1146583
The modems are capable of talking and answering, but only MANYALLY.
All the game's I've ever seen, set the modem so that it will answer after a RING. Since you'll never be able to "ring" the phone, the game will never know when the other computer is "calling". and if you try a DIRECT CONNECTION, it'll never issue the ATD and ATA commands to the modems. It's probably issuing an ATS0=1 to the modem now, and that tells the modem to wait for a ring and then answer.. Since the modem will never get a ring, it'll never answer.

Hope this clears this issue up.
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Author Comment

by:rifraph
ID: 1146584
So there's no string to make the modem answer without a ring?

Thanks for your time.
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LVL 3

Expert Comment

by:jlove1
ID: 1146585
Actually there IS a string to make it answer without a ring. IT's ATA, but the games dont issue an ATA command, because they issue an ATS0=1 and wait for the modem to return "CONNECT AT 19200" or whatever..

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