A modem is a complex device that transmits digital information. If the modem is analog, it converts the original digital signal into analog pulses, and then a special modulator will change their characteristics - frequency, amplitude and phase.
In order for the information to reach the user, the analog pulses pass through the demodulator, which are converted into the original digital signal. There are various types of modems that perform many functions. These devices are internal and external. An internal analog modem fits into the computer case and connects directly to the system board. An external modem is a separate device that connects to the serial or parallel port and is powered from the mains.
Modems work according to special communication protocols, which are divided into several groups. Each of the groups is responsible for certain parameters. For example, the first one receives an analog signal and controls its encoding. The second one checks the encoded signal for errors, and if there are any, requests its retransmission or issues an error report. In both cases, the device will disconnect and report an error number or a request to reconnect.
The third group of protocols is responsible for organizing the connection and data exchange between the computer's RAM and the modem - it sets certain rules and commands. Knowing the encoding of transmitted errors, you can understand the reason for the shutdowns. If you connect a new device, leave the default configurations or make the settings described in the manual.
If intermittent errors occur when trying to connect, you can check them using standard commands. For example, the modem does not dial the number, error: "No line signal", check with the command on the keypad X3 (X0). Keep in mind that this method is useful only if the device is connected and in working order - a long beep is heard, but the dial tone is ignored.
You made sure that the modem is working properly, but it turned off before the start of data exchange - this could happen due to a very quiet or very short PBX signal. Try typing X2. Keep in mind, if the device does not have the desired sensitivity, then the function will not help.
It so happens that the modem turns off while checking the username and computer. Check the timeout value configured for this connection - it is most likely too short. To change the value, open "My Computer", "Remote Access", right-click on the connection icon and select "Properties" In the menu that opens, find the "Settings" button and select the "Connection" tab. Change the numerical value opposite the line "Cancel call when there is no connection" or uncheck this box.
Communication interruptions can be caused by poor line quality, interference, periodic signal fading, limited data transfer rate. Connection errors are eliminated by setting the necessary settings, which are selected in accordance with the manual for a particular modem.