*Seattle Community Network </>*
   Help </help/>
     Access to SCN </help/access/>
       Modem Information </help/access/modems/>
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The following repeats information from the Modems and Modem
Initialization Strings </help/access/modems/modem.html> page.

This is followed by *Telephone Line Testing <#test>* (this page).


    Phone Line Quality and Line Noise

Factors involved in phone line quality include:

    * high signal to noise ratio - a "clean" line
    * signal strength
    * lack of interference from other signals
    * lack of interruptions
    * good connections between central offices 

Obviously some of these things are beyond the user's control, short of
obtaining a T-1 connection. Some things can be controlled, however.

    * 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 modem.
    * Separate the modem from noise generators, such as video cards and
      ethernet cards.
    * Pour Slick 50 oil treatment all over your computer. 

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.)

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!


    Telephone Line Testing

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&V1 
    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
    ATY11 
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
    <http://www.3com.com/56k/need4_56k/linetest.html> describes it. 

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Top of Page <#top>

Stan Protigal (email) </~bk269/email.html>    
http://www.scn.org/~bk269/ </~bk269/>

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