The Process
In a normal connection, the following things happen (in this order):
Windows asks the modem if it is being used
The modem is initialized.
The modem dials the number
The number is routed through the phone lines
The modem negotiates a connection with the server
Authentication occurs
A TCP/IP session is started
Each step presents the potential for something going wrong, and various error
codes can be returned. Identifying at which step the connection failed is the
most important part of teching the problem. Understanding what happens during
each step and why each step might fail is crucial to effectively teching
connection problems.
Step 1 - Windows asks the modem if it is being used.
Windows goes to the COM port where the modem is installed, and
asks the modem if it is being used. If the modem says it is available, Windows
has the modem dial the connection.
Reasons for failure:
the modem thinks it is currently is use
failure returns Error 602 (port already open)
the modem is not installed properly on the COM port
failure returns Error 633 (port not available) or Error 666 (device not ready)
Step 2 - The modem initializes.
The modem first executes the commands flashed into the modem
itself. Then it executes the commands listed in the modem driver. It then
executes any additional commands entered into "Extra Settings" in the
Modem Properties.
Reasons for failure:
the modem doesn't recognize one of its built-in commands failure returns Error
630 (hardware failure)
the modem doesn't recognize a command in the modem driver failure returns Error
630 (hardware failure)
the modem doesn't recognize a command in "Extra Settings" failure
returns Error 630 (hardware failure)
Step 3 - The modem dials the number.
After successfully initializing, the modem dials the number.
Reasons for failure:
the modem isn't properly plugged into a phone line failure returns Error 680 (no
dial tone)
the phone line devoted to the modem is being used failure returns Error 680 (no
dial tone)
Step 4 - The call is routed through the phone lines.
Hopefully, a valid access number was dialed correctly, according
to telephone company routing rules. If not, you will probably receive an
operator message.
Reasons for failure:
an office routing system is unable to route the call as dialed failure returns
Error 676 (line busy)
the telephone company is unable to route the call as dialed failure returns
Error 678 (no answer) and an operator message the number was dialed correctly,
but isn't a valid access number failure returns Error 629 (remote disconnection)
there is no modem available to connect to failure returns Error 676 (line busy)
Step 5 - The modem negotiates a connection with the server.
The modem then initiates a conversation with one of our modems.
They attempt to agree on a compatible protocol to use to make the connection. If
they are unable to agree on how to make the connection, the modem is supposed to
suggest a connection using a slower protocol than the one previously attempted.
Reasons for failure:
the server doesn't understand the modem's protocol (Kflex) failure returns Error
650 (server not responding)
the server refuses to accept the modem's protocol, due to incompatibilities
failure returns Error 678 (no answer)
the modem was disconnected while establishing connection failure returns Error
629 (remote disconnection) or Error 645 (internal authentication error)
Step 6 - Authentication.
Once they agree on how to make the connection, the server
demands that the modem prove that it really deserves our modem's precious time.
It asks for a User Name and Password that it recognizes. If the server happens
to be in a patient mood, it will repeat the question upon failure. If not, it
will tell the modem to go away.
Reasons for failure:
the server is patient and doesn't validate the User Name or Password failure
results in a prompt for User Name and Password repeated failures can result in
either Error 635 (unknown user) or Error 691
(authentication failure) or the server losing patience the server is impatient
and doesn't validate the User Name or Password failure returns Error 629 (remote
disconnection)
the server doesn't understand the authentication info it was given failure
returns Error 645 (internal authentication error)
the modem doesn't get a response from the authentication server failure returns
Error 718 (PPP wait timeout)
Step 7 - A TCP/IP session is started.
Now that all other details have been taken care of, the only
thing left is to actually make a connection that can transfer data. Connections
must use the TCP/IP protocol. Again, the modems must be in agreement as far as
exactly how to use TCP/IP for data transfer.
Reasons for failure:
the DUN connection settings are invalid or corrupt failure returns Error 629
(remote disconnection)
the TCP/IP protocol is not installed on the computer failure returns Error 731
(protocol not configured)
the DUN networking components on the computer are corrupt failure returns Error
720 (PPP no protocols configured)
the TCP/IP stack on the computer has become corrupt failure returns Error 731
(protocol not configured)
This page was last updated on Sunday, December 03, 2000 .
If you have any comments, suggestions or questions Email: [email protected] or [email protected].