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Modem Basics

Links:  Modem Overview | Settings | Init Strings | Drivers | Common Problems | Troubleshooting Steps |

    Advanced Links: Modems In Depth | Init-Strings In Depth | Drivers In Depth |


Basic Modem Overview

Modem - A hardware device usually attached to a computer which allows the computer to communicate with another remote modem over a telephone line. A modem does for computers what a telephone does for humans. Just as a telephone set allows two humans to speak to one another over telephone wires, a modem allows two computers to speak to each other over telephone wires.††For an advanced discussion of modem technology, click here.

Three things that can affect your modem's functionality are:

Settings - Speed & Flow Control can affect slow throughput, or even getting connected in the first place.
Init Strings - Commands to alter the way your modem acts.  This is a step deeper than Speed & Flow.
Drivers - Software that allows your Windows OS to speak to your modem.  Reinstallation is often required.


Modem Settings

Two modem settings in particular can really affect your modem's performance:  Maximum Speed and Flow Control.  Slow performance, sporadic behavior, or even getting connected can all be influenced by these two settings.

Speed - By default, Windows sets your modem's speed to 115200 bps. This is more than double the speed of a 56k modem. In fact, actual speeds obtained with a 56k modem are typically less than 42k, and often less than 28k. If your PC is trying to speak to your modem two to four times faster than the modem can actually handle, your modem's performance can degrade.  Most people actually see higher throughput by slowing their modem.  So, it's best to set the modem's speed no higher than 57600.  

Flow Control - Most modern modems are Internal Modems (PCI slot) and require special settings in order to function properly. This is because they are "software-driven" modems (a.k.a. - "WinModems"). "WinModem" is a widely used term to refer to any modem that does not handle all of the functions of a traditional modem, but depends upon an operating-system driver in order to work. Click here for an Advanced Discussion of Software Modems.

  • External modems, V34 modems and laptop modems are highly unlikely to be "Software" modems.

  • Internal modems are most typically "Software" modems.  If the name of your modem contains the words "56", "v90", "Soft", "Win", there is a very strong chance it requires "Software Flow Control".

  • The most common "win" modems are:

        Win Modems
        Soft Modems
        HSP Modems
        LT Win Modem
        Lucent Win Modem
    US Robotics 56k Win Modem
    Rockwell/Conexant HCF, HSF, Soft56
    AMR Modems
    many USB modems
    SupraMax 56k
    Motorola SM56

How To Change Modem Settings:

Windows 95/98

Windows ME

Windows 2000

Windows XP


Init Strings

Before your modem dials a phone number, your computer software initializes your modem by sending it a series of commands (strings or AT commands) known as initialization strings (commonly referred to as init strings).  Strings configure the modem's parameters for error correction, data compression, flow control, etc. 

You can add init strings to change the operation of your modem. These are typically not required, but can be useful in correcting connection problems. 

Init strings can be used to force a V.90 56k modem to act like a V.34 33.6k modem, which often improves throughput.  V34 is much more stable and handles older static-prone phone lines better.  If you are already connecting at under 34k, you should experience higher throughput and more stable connections by forcing the modem to use V34.

Note:  Before trying init strings, try altering Maximum Speed & Flow Control, as described above.

Once you've done that, click here for an Advanced Discussion of Init Strings.



A driver is a small piece of software that works in conjunction with your operating system to communicate with a specific piece of hardware i.e., printer, sound card, video card, modem, etc.  Each time you install hardware, there must be a driver to accompany that piece of hardware.  However, just as with any software, drivers are prone to bugs, corruption, and various incompatibility issues with the operating system.  For this reason, hardware manufacturers upgrade their drivers to improve compatibility and performance.  Modem initialization strings can also improve compatibility and performance.

Before upgrading your driver, try changing the Settings or adding Init Strings.

Once you've done that, click here for help with finding and installing drivers.


Common Problems

Problems Causes
    * Frequent Disconnects
    * Slow Connection
    * Connect but canít browse
    * Computer not receiving response from modem 
    Bad Modem Drivers
    Bad init strings 
    Bad Settings


Problems Causes
    * Computer Not Receiving Response from Modem
    * No Answer
    * No dial tone
    * Unable to Open Communications Port
The Modem is Being Used by Another Dial-Up Networking Connection or Another Program.
         Disconnect the Other Connection or Close the Program, and Then Try Again.
    Ghost Modems

HCF modems are partially hardware and partially software modems. 
        Rockwell says that they need "hardware data flow" so try that first.  
        Try "Software Data Flow" if it doesn't maintain the connection.

Lucent Win Modem on WinME

There is a problem with the modem drivers for the Lucent Win Modem on Windows ME. If the default drivers are installed, you will not be able to connect with Software Flow control. You will get error 650. Disabling error compression will let you connect but you will get a slow connection and will be bumped off quite frequently. The connection will be very unstable without error compression. Lucent has released a new driver and you can also use the old Win98 driver. There is some information about this here: 

This only happens if the computer manufacturer installed the driver that comes with ME. Please note that this is only a problem on the Lucent Win Modem and not the LT Win Modem. To find out if you have the wrong modem driver, configure the modem correctly and try to connect. If you cannot connect with software flow control, you need to get the newer driver. Disabling software flow control and/or error compression is a temporary fix that will let you connect but this leads to unstable connections and poor performance.

We have had luck getting the default driver to work by setting: error control ON, flow control on HARDWARE, an init string of "AT&F" and 3 commas after the phone number. That should allow you to connect to get an email or download a modem driver. If not, you could try an init string of ATS37=19, ATS37=13 or AT+MS=V34 to force a 34k connection. 


Troubleshooting Modems:

Most modem issues can be handled in the same fashion.  The steps below provide a generic guideline.  Try one step at a time until the issue is resolved.

1) Physical    -    Is the modem plugged in to the correct phone jack?  There are typically two ports on the back of your computer labeled "Phone" and one labeled "Wall".  The other one labeled "Wall" is to be plugged directly into the wall jack.  The one labeled "Phone" is for a normal handset.  If you have a phone plugged into the port labeled "Phone", you should be able to hear a dial tone.  If plugged into the wrong port, errors range from "No Dialtone" to "Busy Signal" to "Not receiving response from modem."

1.5) rnaapp    -    ctrl+alt+del will open Task Manager.  Check for rnaapp.  rnaapp is a telephony API written into the os. It handles dialing out, maintaining the connection, and closing the connection. Rnaapp frequently fails to unload itself from active memory under WIn98 (both versions).  This will give errors like "Modem already in use", "Port already open", "No Dialtone", or other modem-related errors.  Select rnaapp (in Task Manager ctrl+alt+del), and then click "End Task".  This will free up rnaapp from whatever application is holding on to it.  Rebooting should do this as well.

2) Maximum Speed    -    The maximum speed should be no higher than 57600 for 56k modems.  Remember, slowing down the rate at which your computer communicates with your modem causes fewer error and fewer retransmissions, and thus higher throughput.

3) Flow Control    -    It's sometimes difficult to know whether your modem is truly a software or a hardware modem.  So, a little trial and error is often required.  Try software flow control for most 56k modems in Win98/ME (HCF modems are most notable exception).  Problems like "Can't Connect", including Error 629, 650 are often seen.  Also, "Connect but can't browse" problems can occur.

4) Init Sting    -    Some modems simply work better with init strings.  The init string section above contains info on some init strings that seem to work well for some common modems.  Remember, forcing your modem to use V.34 (28.8 kbps or 33.6 kbps) instead of V.90 (56kbps) often gives a more stable connection with higher throughput.  Also, newer V.92 modems often need to be forced down to V.90 when connecting to ISP phone numbers where V.92 is not supported.

5) Re-Install (for XP only)    -    Windows XP maintains an up-to-date (usually) database of modem drivers.  So, you can easily re-install the driver.  Go to Control Panel->Phone & Modem Options->Modem Tab, click Remove, then reboot.  Windows XP should automatically re-install the modem.  Click here for screen shots.

6) Update Driver    -    For all versions of Windows, you can easily update the driver to the latest version.  The difficult part is finding the driver.  If your computer came from a major PC Manufacturer, you're in luck, as these drivers are easy to find.  If you replaced your modem, or did not purchase the PC from a major manufacturer, you may spend a bit (to a lot) of extra time locating the driver online.  Click here for help finding your modem's driver.



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