From: floyd@hayes.ims.alaska.edu (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Help with Line Noise
Keywords: Noisey Phone Lines
Date: 16 Apr 92 21:37:52 GMT
Article-I.D.: raven.1992Apr16.213752.23372
Organization: University of Alaska Institute of Marine Science

In article <1992Apr16.163655.5474@nevada.edu> mlcole@nevada.edu (Michael L. Cole) writes:
>
>  i have experienced both of these problems when calling from home.  in each
>instance, i can hear a crackling sound over the modem speaker.  even a normal
>phone call has a crackling sound in the background.  some days it is weak,
>other days it is loud.  i have also noticed that on days when the noise is so
>bad i can't make a connection, that the sprinkler system has been running.
>the phone boxes are located in the grassy areas between apartments and are 
>amply saturated.

I would complain loud and long to the telco about cleaning up
connections in that junction box and making it less prone to water
damage!  What you describe are classic corrosion symptions...

>  the phone company here is CENTEL.  the technicians i have dealt with in the
>past maintain that they, CENTEL, are only required to provide voice-quality
>service -- data-quailty is at the risk of the user.  BellSouth, who maintains
>the campus phone system, are also concerned with voice-quality -- they don't
>guarentee any speed greater than 1200 baud.  our noise problems range from
>300-baud (still a few out there) to 9600-baud.

They are all stretching the truth.  It is true that they are
selling you voice-quality service.  It is also true that your
modem is designed to work well over a line that meets
voice-quality specs.  If you get errors there are only two
possible cases:  1) your modem is out of specs or, 2) your
telephone line is out of specs.  (Lets keep that in perspective...
One error every minute may be acceptable if it is caused by
impulse noise and your line will still be in specs.  You are not
guaranteed a perfect line, just a good one.)  

I doubt their tarif says a darn thing about 1200 baud data at all!
It does define noise and other parameters which the modem was
designed to expect.  Your modem does just happen to be a very good
piece of test equipment to determine the overall quality of a
voice grade line.  And in your case it sounds like it is telling
you the lines don't meet specs!

>   i have been able to identify that the "{" is the result of a bad trunk line
>entering the campus -- i dial the 4-digit on-campus number and the line is
>clean; i dial the same number using an outside line and the noise appears like
>gangbusters.  management is aware and is working with CENTEL to resolve the
>problem.

This is caused by "clock slips" in digital transmission systems.
About every six months the subject comes up and gets a detailed
discussion in this group.  Since the last time that happened was
very recent I'm not inclined to go into much detail on it.  If
anyone needs more info on it, or help dealing with the telco about
it, please send me email and I'll be glad to help.  I will say that
clock slips are a gross trouble condition that should be fixed
immediately.  Any delay of weeks or months is an indication that
someone in the phone company is incompetent.

Floyd

--
Floyd Davidson           Fairbanks Toll Center, Alascom, Inc.