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Tips on Resolving Random Disconnections

Why does my modem randomly disconnect without any known cause?

Random modem disconnections can be an extremely frustrating experience for you as the user and for Miliserv.Net’s technical support staff. It is often difficult to diagnose the reason or reasons your modem is disconnecting because, unfortunately, there are many reasons that modems disconnect randomly. Determining the reason your modem is disconnecting will require some investigative work, and this document is designed to help us begin that investigation.

Defective Cables/Loose Connections: One of the most commonly overlooked reasons that modems disconnect is due to defective cables and loose connections. If you have an external modem, replace any old or cracked cable, and make sure the pins in the adapter connecting the modem to the computer are not bent. Also make sure the cable between the modem and the computer is TIGHT. If you use an internal modem, make sure that the modem card is seated firmly in your computer.

Next, examine your telephone cable between the wall jack and the modem, or better still try replacing it. If portions of the telephone cable between the modem and your wall jack have been stapled to the wall, examine the cable carefully to make sure the cable has not been damaged. Also do not use jack splitters or multipliers (any kind of device that allows you to plug multiple phones into one jack).

Call Waiting: Call Waiting sends a signal to your phone that can cause interruptions in data communications. A simple way to alleviate this problem is to disable Call Waiting if it exists on your phone line. This is accomplished by pre-pending *70 to the phone number you are dialing. (i.e., *70,908-1443). Do not disable call waiting "just in case." Adding *70 to the phone number without having Call Waiting can cause problems when trying to dial the phone.

Weather Conditions: Infrequent disconnects may reflect a temporary change in your connection due to changes in weather conditions. Weather conditions can cause temporary changes in line conditions usually within the first hours of a rainfall. Besides the obvious physical damage due to fallen trees, etc., studies have shown that excessive rain can cause increased line noise(discussed below).

Line Noise: Another common cause of disconnects is line noise. Line noise can be created inside your home by appliances connected to your telephone line or appliances within close proximity to your telephone line.

To determine if something in your home is causing line noise, try unplugging EVERYTHING connected to your phone lines: caller ID boxes, extension telephones, cordless telephones, answering machines, other modems, fax machines, or any other appliance connected to your phone line. The modem should be the ONLY thing connected to your phone line during this test. If the problem goes away, one or more of those appliances connected to your phone line is probably causing you to disconnect. You can try reconnecting the appliances one by one to isolate the one causing the problem.

Line noise may also be introduced into your phone line by nearby electrical appliances or radio transmitters. Telephone lines are very sensitive to inductance or voltage produced by nearby electric appliances/lines or radio transmitters. To protect your modem from inductance, do not route the phone line within three inches of any electrical cord, extension cord, computer cable, printer cable, monitor cable, or any electrical appliance or power supply. Especially avoid laser printers, cordless telephones and uninteruptible power supplies (UPS's). If necessary, tape the phone line more than three inches away from the items listed above or any other electric appliance within close proximity to your telephone line.

If the line noise is not being induced inside your home, it may be induced in the cable somewhere between your house and your local telephone exchange central office. Your line may have one or more of conditions the telephone company calls 'bridge,' 'ground loop,' 'cross talk,' or 'bad loading coil.' Any of these conditions will cause random noise and unpredictable disconnects.

For noisy lines, try increasing a setting that tells the modem how long to wait (in tenths of a second) before hanging up when it loses carrier detect. According to modem manufacturers, "This guard time allows the modem to distinguish between a line hit, or other disturbance that momentarily breaks the connection, from a true disconnect by the remote modem."

For example: S10=100 setting will make your modem wait 10 seconds to make sure the other modem is really gone before hanging up. To change this setting, go to the following:

Start > Settings > Control Panel > Modems > Connection > Advanced Connection Settings > Extra Settings. Type S10=100 in the Extra Settings box.

If this seems to help, call your phone company and request that the line be checked for noise at the network demarcation block at your house. Do not let them just check the line from the central office end. Ask to meet the repairman at your house and get him to report the results of his tests to you.

Connection Speed: Surprisingly, the most common cause for modems to disconnect randomly is connecting at TOO FAST a speed. You may be surprised to learn that your connection speed varies during the course of your being connected to While the speed at the time of your connection may have been 44,200, this speed varies while you are connected due to line noise and errors. When your modem detects noise on the line, it attempts to reset itself to its optimum connection speed through a process known as ‘retrains.’ When the modem is unable to reset itself, your modem may disconnect.

The Modem itself: Not all modems are created equal.  HSP Modems:: Rockwell HCF Modem, Lucent Technologies (LT WinModem), and USRobotics 56K Winmodem are software driven modem.  These modems use a software driver by the host computers processor  in place of a dedicated Host Signal Processing chip on the modem (DSP) to perform the Digital Signal Processing. 

These modems work by using a specified percentage of the CPU, by utilizing a portion of the unused instruction cycles of the CPU, to process data from the modem.

If you have applications running in the background, when using the modem, you will have less CPU time available to process information to and from your modem.  This can have an influence on the modems performance and it's ability to maintain a connection.

We see more of this type of modem with connection problems than the ones with a dedicated Host Signal Processing chip.