Seattle Community Network
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The following repeats information from the
Modems and Modem Initialization
This is followed by Telephone Line Testing
Factors involved in phone line quality include:
Obviously some of these things are beyond the user's control, short of
obtaining a T-1 connection. Some things can be controlled, however.
- high signal to noise ratio - a "clean" line
- signal strength
- lack of interference from other signals
- lack of interruptions
- good connections between central offices
Most people won't need to do anything (except maybe the Slick 50 56-KFlex
Oil Treatment). If you are getting more-or-less consistent connections, you
are probably okay. If your connect speed is 2400 below the maximum connect
speed, consider it an enhancement to stability. (If you start with a 2400
baud modem and connect at 2400 below that, it will be very stable.)
- Make sure all phone connections are solid
Usually this is not a problem,
but a single loose connection can result in intermittent noise. I had a weak
connection cause misdialed numbers as well as modem problems.
- It is possible to route a phone line so that the first connection is at the
- Separate the modem from noise generators, such as video cards and ethernet
- Pour Slick 50 oil treatment all over your computer.
You may find that the signal levels are not high enough to generate a maximum
speed connection. That's usually not a major disadvantage, provided that the
signal is clean. My own connection was at a consistent low level but also
consistently clean. I'll take that over fast and dirty any day, and besides,
think how much harder it is for my dog to eavesdrop on my conversations!
It is possible to test line quality with some modems.
The test results themselves won't help, because the telephone company is only obligated to provide "voice
grade" service on ordinary telephone lines (sometimes called POT for 'plain old telephone line'). It is possible to
use the data to back up a complaint on voice quality issues. In such a case, you would need to qualify the data by
clearly stating that this is a problem with "voice quality," and that the modem data is there only to
substantiate the "voice quality" problem.
Most common problems involve static and high frequency dropoff. I often have a difficult time getting people to hear
the number 'six' in conversation. My phone lines show a frequency degradation at the high end, and I suspect that if my
line had better high frequency response, others would hear me say 'six'.
To test line noise with the modem, find a known good connection, such as an internet provider with ISDN lines, digital
lines, or 56K capable lines. Some of these tests require that you escape to command mode with the escape code.
The default escape code is +++ (S2 set to ascii 43). You reconnect with ATO (the letter O).
- Rockwell Chipsets
- AT&L - only during a session while in command mode (escape with +++; reconnect with ATO)
- AT&Q - only during a session while in command mode (escape with +++; reconnect with ATO)
- USR modems
- 3Com (USR) Line Test
- 1-847-262-6000, and log on as "Line Test." They give you a nice graphic
representation of your signal response. A 3Com website describes it.
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Stan Protigal (email)