I am trying to write a Modem Dialer Software on SCO unix platform. I have successfully opened /dev/tty1A port and made following port setings
[Server Side]
Input Mode = 0 ( None )
OutPut Mode = 0 ( None )
Hardware Control Mode = 8 Bits , Enable Receiver , Drop DTR when application terminates , Bi-Direction Flow Control
Disable Special Control Characters except START, STOP , VMIN , VTIME

I have successfully got a response from Modem as "OK" for both "AT" & "ATZ" commands. I have connected the Modem to my intercom line. At an other PC i am running the client software which has the same setup for port /dev/tty2A as of Server and a Modem connected at its end which in turn is connected to the intercom line

I am completely unable to transfer data from Server/Client to Clinet/Server PC. When I write "ATD phone_numberW\r" command at the client side , I am able to trace "RING" event at Server side. But after that the code goes for a toss stating at client side "NO DIALTONE" or "BUSY" or "HANGUP".

Kindly guide me the Know how of modem Programming stating
1) How to detect what Modem Make I am using?
2)What is the generic Modem Init strings?
3)What are the sequences of Command to be intiated from Client and Server side to Modem and what will be the EXPECTED responses ?
4) Are my port settings correct ?
5) How can I transfer data from PC to PC using Modems at both ends.

__________________
Regards,
Satya Prakash Prasad

If you have not seen this thread, here's a cool link on Serial Port Programming:
http://www.easysw.com/~mike/serial/serial.html

Thanks for all your help. The material was of enough help to me. But if possible kindly guide me the sequence of COMMANDS that we need to send or operate on Modem both from Client and Server side in order to transfer data successfully.

I am not knowledgeable of the control flow that should occur. As stated earlier I have set Hardware control flow bidirection handshaking ( RTS/CTS ). Do I need to do something extra than this. I somehow have not been able to get what algorithm to use.
If possible kindly direct me with a pseudo logic right from scatch.
I would be enouhg thankful with all my heart. I seek knowledge and ready to slog it out. Kindly help me out.

__________________
Regards,
Satya Prakash Prasad

I've never worked on Communication with a Modem, so I can't really help you with this, though I think the link pointed in the earlier post is really helpful and with a little bit of experimenting, you can achieve what you want!

Rgds
SHAIK

On questions 1, 2 and 3; there is no way to detect what modem you have on a port. You need a configuration file somewhere that the program can read to find out. And each modem will have its own commands that can vary somewhat.

For question 4, your setting are very wrong indeed. If fact, I suspect that your original post contains some typos or something. Read that link that shaik786 provided again.

For question 5, take a look at uucp. This is the command that you seem to be trying to rewrite from scratch.