Galaxynet :: Line Noise Issues
What is Line Noise?
Line noise is static on the phone line. Cellular and cordless phones
have a lot of line noise; it can be heard as static in the background of
the conversation. For data transmissions, particularly at high speeds
(really, anything over 300 bps), line noise can be a major problem. High
speed data transmissions are much more sensitive to noise in the lines, and
can be affected by static that you cannot hear in the line.
Line noise can be caused by several factors. Electro-magnetic
interference is often caused by wiring in and around the connection from
the modem to the wall jack. It may exist in the phone line being used, or
in the jack being connected to. It may be a loose screw on a connector
block somewhere between the customer and the CO, or water in one of the
Telco cable ducts around worn wires. Or, it may be anywhere in the wiring
within the house, apartment complex, or hotel. The age of the building and
its wiring, as well as the age or the infrastructure in your neigborhood
plays a major factor.
Static will get read as data and cause packets to be lost and resent.
At best, it limits the connection speed to something like 31,200. At
worst, it will not allow you to connect at all. Generally, though, it
is something in between and can be very frustrating.
How to Test for Line Noise
The following Dial-Up Networking errors can all be symptoms of line
noise or trunking issues.
- Error 645: Internal Authentication Error
- Error 678: No Answer
- Error 679: No Carrier
- Error 691: Authentication Failure
- Error 718: PPP Timeout
- Error 731: Protocol Not Configured
- Instant disconnect
- Disconnect at variable times
Each of these errors could be something else and should be checked
first. The thing we're looking for is inconsistency. If you
are getting a 691 every time, it's most likely a mistyped user ID or
password. If you get a 691, a 679, then a 731, then connect and get
dropped, it's possibly a line noise issue, but this could also indicate
bad or out-of-date v.90 firmware/driver for your modem.
Listening to a phone line can give you an idea of the noise in the
line. In order for you to hear the line clarity, you need to get rid
of the dial tone. Plug a handset into the jack, lift it off-hook and
press 1. This will give you about 30 seconds of silence to listen for
noise. However, this will not always be helpful, as most line noise is
If you are able to connect, but cannot connect at the speeds you
expect with the protocols installed, line noise is often the problem.
If you get a connection speeds greater than 33.6 and less than 50K,
like around 40K, you should check for line noise.
By following this test you can get an idea of whether the quality of
the phone line, between your home and Galaxynet's POP, is conducive to
making a high speed connection to your ISP. This test will work for many
- Open up Terminal in Windows 3.1x or HyperTerminal in Windows
- At the terminal window at a cursor prompt, type ATZ
and hit the Enter key, even if you don't see anything appear on
the screen. It should respond with "OK."
- Now type ATDT####### (where ####### is your normal dial-up access number) and hit Enter.
- The modem should dial and connect to Galaxynet. You will either
see a "Login" or "Password" prompt. If the
prompt has mixed signals (i.e. "Log#BJDx_in"), there
is noise on the line. If you get nothing but garbled text
streaming across the screen, you definitely have a line noise issue.
- Type +++ but DO NOT HIT ENTER. The modem should respond
OK after a second.
- Type AT&E1&V1 and hit Enter. The modem should
respond with a list of information related to the connection. Look
for a listing as Line Quality and write it down.
- For Conexant/Rockwell modems and others, type AT%L%Q.
The Line Level (%L) is in -dBm and should be less than 24.
The Quality Monitor level (%Q) of 15 or higher mean there are real
line problems with your Telco circuit. You will need to contact the
phone company to have them repair the problem.
- For USR modems, type ATI6 and look for "Blers"
(Bit Link Error RateS) value. It should be less than 3, ideally 0.
Anything higher and you have a line noise issue.
- Type ATH and Enter to disconnect the modem from your ISP.
- Repeat steps 3 through 6 AT LEAST 5 TIMES. This will give you an average
value for the Line Quality between your home and Galaxynet.
Line Quality values greater than 25 indicate that the modem is sensing excessive
line noise. When this is the case, there is usually not much that can be done to
decrease the noise. You may want to contact the phone company to determine whether
they may be able to enhance the line quality.
Reduce Local Line Noise: By local line noise, we mean the line noise
generated by devices and lines the you have setup in conjunction with the modem.
- Remove other phones, fax machines, answering machines, caller ID boxes,
other computers, line splitters, and surge protectors from the
line. Connect the modem directly to the wall jack.
- Clear away all other power sources and wires around the phone line and jack.
If your phone cord is close to the power cord for your computer, desk lamp,
monitor, television, etc., you may be injecting noise into your connection.
- Try changing/replacing the telephone wire between the computer/modem and the
- Try connecting to another jack in your home. If practical, try another location
such as a friend's house, or work (just remember that some businesses use
digital phone systems which are incompatible with analog modems).
Modem Settings: There are some modem settings you can adjust to help deal
with line noise. Many of these suggestions require you to have the User's Manual
for your specific modem. If you don't have your User's Manual, try finding it at
the home page for your modem manufacturer
- Disable 56k v.90 protocols.
- Set S10=100 or higher (no higher than 254)in Extra Settings. This is the amount of time in tenths of a second that the modem will wait before dropping the carrier if there is some sort of interruption in the data flow on the phone line.
- Lower the modem port speed and/or the FIFO buffers.
- Enable software compression (works very well on a Win Modem).
- Enable error control with data compression (some Win Modems will have problems with this).