Dealing with noisy phone lines
Q I have a Web Excel 33600 voice/fax modem. About five weeks ago I was getting 336000bps and 28800bps connect speeds ù but not to send this e-mail. I have the damn thing limited to 9600 or 14400. Telstra has just checked the line and said that it tested perfect (and they only have to supply a 2400bps service anyway). What is the problem? Why is my modem falling in a heap and how can I check its speed? û Peter Woods A Phone lines were designed to carry voice information, not digital data. Modems are used to convert digital data into a form that can be sent down a phone line. Unfortunately, we donÆt just want to send information ù we want to send lots and lots of information as quickly as possible. The faster information gets propelled down a phone line, the more susceptible the process becomes to line noise. Noise can occur anywhere along the way from your modem to your ISP. Different modems are better at dealing with noise than others, and both your modem and that of your ISP have to work together. When there is a lot of noise, the modems might drop back to a lower connection speed. Also, the modems may have to keep resending information that has been corrupted during transmission. This means your connect speed seems high, but the actual transmission speed is reduced due to the continual need to resend data. Sometimes the modems may fail to connect altogether. Cheaper modems can exacerbate the problem. If possible, try your modem on a computer in another location, or try someone elseÆs modem on your computer. Try dialling another ISP (perhaps using a free introductory offer kit). Also, try to eliminate sources of line noise. Listen to the phone line during voice conversations. Does the line sound clear? Sometimes the noise can originate in your own home. If you are using a long phone extension cord, try a shorter one. Make sure the phone line is not near any potential noise source, such as a monitor. And donÆt operate your computer with the case open, as the case shields the noise created by the computer. Other noise sources could include desk fans, fridges, washing machines ù the list goes on. Finding the source of noise is basically a process of elimination. Sometimes faults at your local telephone exchange can cause connection problems. In such a case the quality of the connection will vary. Hanging up and redialling usually fixes the problem. However, in this instance the consistency of your problem would suggest that this is not the cause. û Roy Chambers
Category: hardware, communications
Issue: May 1998