NWA-PCUG Newsletter Article
Telephone Line Quality for PC/Internet Use with Standard Modems
by Grant Wales, April 2000
firstname.lastname@example.org (click to email author)
The line that carries the digital signal from your modem to the telephone office in your area is the "lifeline" that most of us depend on for our internet connection. It can contribute noise of various types which can interfere with good service to your ISP. The connection between the phone office and the ISP is of a much higher quality, and almost never contributes to substandard connection quality.
In general, the longer the line to the phone office, the greater the opportunity for that line to degrade signal quality. If interfering noises normally do not include big impulses (like from intermittent connections or from reasonably close lightning discharges) the user will find that their initial connection speed may be above 45,000 bits per second if they are within 5 miles of the phone office, and correspondingly lower speeds if they are further away.
The phone company has some broadly stated standards for providing sevice for voice and for data. In Arkansas, the standard for PC data connection speed may be 14.4 kbps minimum. For users located some distance from a phone office, they may expect their phone line to limit their speed to 20 kbps or less.
Most users don't do so much downloading that a connection speed of around 25 kbps will be detrimental when compared with a connection speed of about 50 kbps. In many cases, the limiting factor in download speed will be at the sending end, or will depend on net congestion. A user would like to maintain a consistently high connection speed with their ISP to ensure good results when good results are available.
Some of you may have taken your computer to your ISP to help determine how much better it connects to their server modems without the intervening telephone line. In many cases, a much poorer connection when your computer is at home is the result of limitations of the telephone connection from your modem to the phone office.
If you have occasional impulsive noises on the phone line used for data transmission, that may have numerous untoward effects on your ability to obtain and maintain a satisfactory connection to your ISP. Even a line which exhibits mild "crackling" noises if used for transmitting normal telephone voice signals may provide good connection as a data line. However, a web surfer may find that something else is happening which prevents solid data connections. That something else may be another form of noise which occurs occasionally during the data connection.
It is a much more elusive thing to assess the impact of the phone lines when sporadic or intermittent impulsive noises interfere with the ability to make a solid connection. Due to the nature of a condition that fluctuates over time, it may be difficult to have an observer with suitable detecting equipment on hand at the time poor performance occurs. Many linemen will not be able to test whether a given line will provide a connection that will satisfy the user of a faster modem.
Noises from a variety of sources are always present, and if you have a marginally noisy telephone line, the noises can have a direct impact on your abilty to do some very basic things:
access your mail account
maintain your connection (get an inadvertent disconnection)
obtain consistent high speed connections
When a good connection is not obtained, the error messages on your screen are often misleading and may not refer to your phone line quality. The messages tend to point toward a problem at the server. This may color the user's view of what's really going on.
If you have had reasonably good experience with a modem no faster than 33.6 kbps, you may find the use of a 56K modem to be fraught with a host of problems never previously experienced. Your modem and your ISP's modem negotiate for initial connect speed when you log in. The faster modems are more sensitive to noises and may not provide a reliable connection.
There are ways to make settings within your computer to be somewhat tolerant to a noisy line. The ISP can guide you through these settings. However, you may continue to have problems.
To play the part of a sleuth in localizing the source of the problem is not easy, and it may take a lot of accumulated experience to narrow down to the offending contributor. Let's assume that our focus will be on the phone line and on making a determination of how to isolate what part of the phone line is causing the trouble.
In many cases, there is a service box on the side of your house where the interfacing connections are made between the inside wiring and the service "drop" which connects to the line on a telephone pole. There will be one interface unit for each phone line, which has a modular receptacle and wires which are connected at a terminal block to the wire pair in the service drop. A user can open that portion of the box which allows access to the interface unit and connect a phone directly to the interface unit after the modular connector from the internal wiring is removed. This is a positive way of isolating noises (those which can be heard) from the internal wiring and the external phone line. If the noises heard from a phone connection inside the house are not present when connected to the outside line, look for problems inside the house. Some of the contributors to noises may be older devices which hook directly to the phone line, such as wireless phones and answering machines.
Some have purchased a 50-foot telephone line with modular jacks at either end and made the connection directly from the modem to the outside interface box. This can be done by routing the cable temporarily through a window and along the ground.
Suppose you feel there is sufficient cause to call Southwestern Bell to come and check the line and make repairs, as needed. The 800 number rings into a dispatching office in Wichita. If you go through the menu, they take you through a routine where the recorded message warns that if the problem is found within your home, you may end up paying for the service call. They may perform some kind of test on the line number that you designate. This may or may not be a definitive test -- it may not give a result that addresses your problem. If you pursue the call to it's conclusion, the recorded message tells you that a repairman will appear before 8 PM (that day if you call early -- the next day if you call late). If you hit "0" during the menu or just stay on the line, you'll get someone to talk with.
The lineman or service technician has a simple instrument that is frequently used to check for shorts and opens on a line. It can also apply certain kinds of stresses (loop currents, etc.) The lineman tends to make repairs or swaps of this or that on accessible connections (including on the poles). In many cases, their measurements may not address the concerns experienced on that line (e.g, an intermittent condition not present when he is checking).
Many service drops are buried. About 20 years ago, an improved 4-conductor buried cable started to be used. This helps ensure that moisture and it's corrosive effects were less likely. Of course, a few things may have happened to the buried cable to compromise the impervious plastic sheath. Perhaps an excavation by another utility installation resulted in a break and a non- weatherproof splice, perhaps a ground squirrel got cold and hungry and ate some of the insulation.
There is a device that can be used to detect the location of a discontinuity in a wire line, if the discontinuity is sufficiently bad. It is called a Time Domain Reflectometer (TDR). It sends pulses into one end of a line and presents an oscilloscope trace of the characteristic impedance as a function of length along the line. Thus, it may be used to diagnose and locate a fault, even in an underground line. A TDR is not often used. A temporary line (laid on the lawn) which bypasses the service drop is infrequently used between the pole and the house unless trenching in a new line seems inevitable.
In my case a dramatic improvement was noticed in the data line after the replacement of the interface units. The interface units are quite inexpensive and are recognized as a source of likely future problems if they are allowed to get wet. This replacement happened quite by accident, and was the result of my careless use of a temporary 50-foot phone line which entered the open box. I allowed the box to remain open overnight and it was exposed to rain. The local repair technician arrived in the morning and saw the inside of the box in it's wet condition. We had a prior arrangement to work together in resolving my problem, and he came in the morning to check on the results of my experiment with the temporary phone line. The buried service drop and the interface units were the only items that had not been replaced over the years of calling for repair service.
A fairly common situation is for the lineman to make the repairs thought to be the most needed and for the user to follow up with a later phone call for service, if needed. They usually expect you to be at home to let them in the house if needed to verify the cause of a problem if it seems to be inside.
There are supervisory people on hand in each city, in Wichita, and in Little Rock where the president of SW Bell presides. Names and numbers of those I've contacted are:
Rogers: Mike Gantrell -- 501-636-7505
Wichita: Ken Flowers -- 1-888-287-1395
Little Rock: Cory Anthony -- at the "hot" line that goes to the
I think the local supervisor can call for the use of a TDR measurement.Click here to return to top