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Troubleshooting Modem Errors - Dial up

Troubleshooting Modem - is the device dead, disconnected from the computer, or bad drivers?

Modems are a great addition to your tools for your computer.

Troubleshooting problems for Dial Up...

In this digital age of Broadband (DSL / Cable) and Wi-Fi there is still a need for a dial up modem, don't be fooled there are a lot of places where Wi-Fi and broadband is not readily available or cheap!

Dial up Modems:

Most modem problems are not due to hardware but software. By this I mean that the modem is a very simple device. It takes a bit from the computer (digital) converts it then sends it across the phone line (analog) to a receiving modem (digital). This is accomplished by changing the bit from a digital signal to an analog signal. Think of it this way you have a ball and you want to send it to someone in another city. Would you wrap the ball in shipping paper then send it off? No, you would put it in a box and the wrap it in shipping paper to send it.

Take the analogy and reverse the ball and box. Digital signals are a Square Wave (a box), Analog signals are a Sine Wave (a ball, a sign wave is three hundred and sixty degrees but instead of being a circle it is half the circle up and half of the circle down like this symbol: ~.

The modem takes the digital bit, converts it to an analog equivalent and then transmits that signal to the receiving modem which turns the analog bit back to a digital bit for use on the receiving computer.

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When you are experiencing problems with a modem the first thing you will want to look at is the software. Just like networking the first step is to insure the software is working correctly.

Troubleshooting Modem Instructions:

Most modems either internal or external have software called drivers, this software is what takes your command, converts it to the correct protocol and then sends the information on it way.

Troubleshooting Modem how it works:

  • There are three levels of drivers, User Interface, Intermediate Interface, and Hardware.
  • User interface is any program that can use the modem to transmit data.
  • Intermediate interface is the go between the User interface and the hardware.
  • Hardware is the modem and/or the port that it connects to  internal or external.
  • When you decide to send data to another computer by modem three things have to happen:
  • You have to initiate a program that is modem aware, some of these are your email, your browser, or your VPN.

  • Next the program will send the data to the intermediate interface, this will in turn convert the digital data to analog, send the dial sequence to the hardware and wait for the 'handshake' of the protocol that the other modem has answered and is ready to receive the data.

  • The hardware takes the initialization string from the intermediate interface, parses the information and sends the dial sequence to the phone line. Once the modem receives the dial tone, it dials the phone number to the other modem, it then waits for the receiving modem to answer and send the acknowledgement that it is on line ready to receive data.

Troubleshooting modem errors:

We are on line but will the data transfer from your computer to the other computer at the end of the phone line?

  • Symptom: Your modem is installed but when you dial out you don't get a dial tone.
  • Cause:
  • The telephone cable not in the correct port.
  • Having to insert a 9, before the telephone number to get an out side line.
  • The modem is assigned the wrong com port.
  • The modem did not initialize when the computer started (internal modem)
  • Fix:
  • Check that the telephone cable is not in the Network cable port

  • When you setup the dial up number insert a 9,, (nine is for the outside line where you are located, the two commas are for a one second pause for each comma to give the telephone switch board time to switch to an outside line.)

  • Your modem can operate on one of four com ports, 1, 2, 3, 4; this port number must coincide with the physical port in use by the modem. If it is an external modem it will connect by cable to the computer serial port which is numbered. If it is an internal modem then the physical ports in the computer take precedence when the computer starts unless you change the port numbering in the system BIOS setup - not recommended.

  • If the modem is internal when the system starts it will power up and tell the computer BIOS it is on line and ready, at that time BIOS will assign the com (serial) port, this must match the modem if there is a conflict the modem will loose and will have to take the next available port. This is an unusual occurrence, only happens when a parameter has been changed in the BIOS.

  • Troubleshooting Modem Com Port conflict resolution and general troubleshooting:
  • Internal modem port conflicts have to be resolved by first checking on the physical port assignments then changing the modem to the next available port. You can only access the serial port assignments through the Computer Management console. Click on  the Device Manager, in the right window click on the Ports (COM & LPT) you will see the Communications Port (Com1) or more. If you have four com ports you will have to disable one in the BIOS for an internal modem to work.
  • You access the Modem setup through the Control Panel 'Phone and Modem Options'.
  • Troubleshooting Modem Dialing Rules - location:
  • General tab you can set the dialing Area Code,  the number (as in 9,,) to access an outside line - use this only if you have to dial the 9,, every time the modem dials. And so forth.
  • Under the 'Area Code Rules' tab you would insert any rules that your telephone company would provide for you to connect.
  • Under the 'Calling card' tab you would enter the information for a pre-paid calling card.
  • Troubleshooting Modem Modems tab
  • In the window your modem should be listed both internal and external.
  • General tab
  • This fist page will tell you what port the modem is assigned to, the make and if internal the PCI bus number, device number, and function number.
  • You can use the Properties button to access the different tabs, the one you are most interested in is the Diagnostics tab.
  • If you are having problems and need a log then check the box for Logging this will give you a text file for further analysis.
  • To test the modem with out dialing a phone number press the 'Query Modem' button. This will test the three levels of protocol with out dialing or transmitting any data. It is quite comprehensive. You can see what the modem is doing and see any errors in the window above the 'Query Modem' button.
  • Under the 'Advanced' button is where you can change the assigned com port in case that is what is causing your modem problems. Click on the 'Advanced Port Settings' a new page will open. For the most part the setting here are already at optimum. On the 'Port number' is a drop down list, you have a choice of 32 serial ports. Don't believe this your modem will only operate on four ports. Select the next available port from the physical ports in the computer. (from the Device Manger) if the last port was 1 then you should use 2, if the last port was 3 then you would use 4.
  • Also under the 'Advanced' tab is the 'Change Default Preferences' button when the page opens you can change these parameters: Cancel call if not connected in xx seconds, Port Speed, Data protocol, compression, and Flow control. These items should only be changed if instructed to do so from a tech support person or if you install special software that requires them to be changed to work with that software.
  • If your provider or program requires special 'Ack commands' you would enter them in the 'Extra initialization commands:' window.

Troubleshooting Modem Power Management tab: Allow the device to bring the computer out of standby. This can be checked if you have the computer setup for remote control and use a dial up modem to activate it.

Note: Use this option with extreme care, a hacker finding that the modem will start the computer could use it as a 'spring board' computer for hacking other computers and the only people that would know about this would be the hacker and maybe the ISP you use (which is hard to prove!)

Troubleshooting Modem Driver tab: This will be where you check the drivers that are loaded for the modem and you can also update the drivers or uninstall the modem if you are doing troubleshooting and want to see if the drivers are the problem.

Most modems now come with a setup program that will install the correct drivers, check and set the correct serial port for the modem to operate on. If you are having hardware problems with your modem the best thing to do is disconnect or remove the modem from the computer. Restart and using the Device Manager uninstall the modem. Power down and reconnect or reinstall the modem, have the install software and restart the system. Go through the setup process again.

When Troubleshooting Modem errors observe ESD!

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