Dec 092017
An excellent tutorial on line noise and why it happens.
File ALLNOIS2.ZIP from The Programmer’s Corner in
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An excellent tutorial on line noise and why it happens.
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Contents of the ALLNOIS2.TXT file

=-=-=-=-=-=-=- Av-Sync Bulletin 8 : Line Noise & You -=-=-=-=-=-=-=
Download as BLT8.TXT Last update: 5-28-89

This was a difficult bulletin to put together.
So many people have mis-conceptions of what line noise is. Most often,
they blame it on the place they are calling rather than looking within
their own back yard, or the environment from point A to point B.

"What happens between your modem and the other end?"

We will try to answer most common questions covering these areas:

Calls from HOME
Calls from the OFFICE
LD Services (Name your calling card!)
A typical connect path

I am not a super-mogul of communications, but after many calls to the
right people, some accurate info has been obtained which may be useful.
All of this is designed to educate the novice while not insulting the
people who have a full understanding of modem communications.

Disclaimer: Some of the comments may be pointed, but they are as true
as can be proved by the people (internal) at various BOC's and switching
offices. Several key people with AT&T have cooperated in the compilation
of most info here. I feel that the user of any phone service has the right
to know what the score is, and any provider of said service, being a PUBLIC
service, should be more than ready to help any of its users.


We run a fairly large system here. The concern is always for the user.
As usual, we try to apply the latest technology we can afford. Because
there is such a turn-around in the industry, we prefer to wait rather
than "jump" onto a new product, version of software, modem, etc.
Once the product has proven itself, we will consider it.

AV-Sync runs with either Hayes SmartModems (2400) or USR HST 9600,
Depending on the node. The main dial-in number operates via Hayes
2400 since that is the top speed for most first-time callers.
The modem has proven itself to be reliable and bulllet-proof to most
problems generated by outside callers and MA BELL.

The next number (in rotary) and all other numbers run with USR HST
modems. We decided on USR because they seem to be the front-runner
so far as 9600 access goes. One (1) V.32 CCITT standard is now on line
for users who want to experiment. We don't plan to expand to more
V.32's any time soon. The market just doesn't warrant it.

The "WHO WILL WIN" scenario probably depends on whether HAYES or USR
is successful in their bid for dominance. Frankly, it will be a tos-up
as I see it. USR is doing well with the dual standard, while Hayes has
been under-cutting USR's prices to SYSOPS... good marketing, but not
quite there. The market as of this date is mostly in the northeastern
U.S., and not widely spread otherwise. Hayes' newest bid will be fun
for some SYSOPS who want to be the latest and greatest, but it is
obvious that normal consumers simply cannot afford the latest techno-
logical items. SOME 9600 standard will surface, and it will be compat-
ible with the ones in use by the majority. I predict USR.

For the longest, the Germans have had a true standard. Most business
concerns and major services will move toward their convention, but the
U.S. consumer will move toward the next best item, and the least
expensive one. Undoubtedly, you will see some great deals on modems
in the months to come. Alost anything in the 2400 baud range will work
well. MNP modems? (Take another look at the Craps shoot.)

Statistics for AV-Sync indicate: 1200 baud callers @ 18%
2400 baud callers @ 55%
9600 baud callers @ 22%
300 baud callers @ 3%
ODD baud callers @ 2%

This stat is accurate as of 5/28/89. We decided to go with the 9600
standard because the USR's work well at 19.2 and and are downwardly
compatible. (They don't usually have to "wake up" to the next caller.)

Lines IN/OUT:

All incoming lines to AV-Sync are among the cleanest in Atlanta. We have
the circuits checked weekly as a policy. Rarely, there will be noise on
these lines owing to bad weather (humidity does strange things to
copper wire). As well, when the local exchange (404-32) is constantly
changing. Other users of this exchange include the National CDC, Emory
University, and several government services.

It isn't the local phone company's obligation to tell us if service may
be interrupted for installing a new trunk or some internal switch.
They aren't obligated to tell us when THEIR software fouls up;
(usually at the early AM update/scan if at all).
We have to find these things out for ourselves.

By the same "token", it isn't their obligation to tell the user if the
incoming call is from an old trunk (inward) or some adjoining local
exchange. What do they connect to? Well, it isn't a local BOC's policy
to tell you when you are on a bad or old circuit, or on a new circuit.

Depending on time of day, and how busy your local dial-up is, and what
you have decided on for a carrier, you may get a bad connection to
wherever you try to call. (Craps shoot again). More of this, depending
on where you are, and who CALLS YOU, or where YOU CALL, depends on what
your local BOC is doing with THEIR carrier.

In some areas, a GATEWAY, or local avail dial-out is available.
Personal opinion: PC Pursuit is all but dead, while StarLink is trying to
do it right. Time will tell.

Particulars for PCBoard software and almost any modem:

A "NO ANSWER" may mean one of two things:

The caller is using an automatic dialer to access the system,
and the system is getting modem errors, causing it to try a reset
WHILE the caller is dialing repeatedly. This isn't usually
productive, but many people don't understand that.

A node is down in the rotary, and the software (source end) failed
to place the modem "OFF-HOOK", causing a busy signal which would
tell the phone company to go to the next line in the rotary.
Instead, a "dead ringer" happens, and users may only access
a source if some unfortunate person is calling the dead line,
thus tying it up and forcing the rotary to the next free node.

This problem is common on many systems. The local phone company
(YOURS or OURS) may also cause this to happen. That's why
you might call a VOICE number sometimes, expecting an answer, and
it just rings and rings. "I tried to call you, but there was no
answer!". >> "That's funny, I was here all the time and didn't
hear the phone ring!"
This is just the way many phone companies (BOC's) cache their
services and resources. On occasion, a few users go to NOWHERE
LAND inside the all powerful MA BELL.
You may also try a call and get another number. It isn't always
dislexia or a manual mis-dial..... sometimes MA BELL's software
just gets a digit wrong. Again, this depends on where you are,
and where you call.

Calls from HOME:

The MOST common problem we've experienced from home-based callers is
line noise or dis-connects induced by someone picking up the phone, or
the user forgetting to cancel CALL WAITING where available.

Your local phone company will have that information. Some BOC's provide
different codes for call waiting. They range from CANCEL until user

Many users who are just beginning to use modems have purchased the best
buy at their local computer outlet. Often, these "best buys" can provide
nothing but headaches. Typically, they are discontinued models because the
manufacturer either found a bug or dumped a line for better technology.
The reseller received a good liquidation deal and passed the modem, along
with its problems, to YOU. This isn't true in all cases, but the range
of compatibility and potential problems is enormous.

Coming from the shadows, ANY v.32 standard modem will talk to the new
US Robotics dual standard modem. (No advertisement intended, but an
example.) So, if you have a v.32, you can connect with this modem on
the other end. If you got a bargain basement brand, usually 1200 or
300 baud, the only thing that the manufacturer had to do in most cases
to claim HAYES compatibility was to include the AT command and other
very basic modem communications standards. Then, most of them will
go in their own directions with "& this & that & whatever".

This is not to say that you should buy the latest and greatest modem,
but a few opinions from friends wouldn't help. Though most newer models
aren't entirely perfect, the average is better these days.

If you have a known GOOD modem, you may have a configuration problem
with the software you are using to call out. Understanding of proper
FILE TRANSFER PROTOCOLS is important. The best two averages are YMODEM
and ZMODEM. Others are good, but less reliable in many cases.
Again, AV-Sync prefers to go with tried and true protocols rather than
the latest thing out there.

Check your configurations carefully, and insure that your download
(Receive Files) paths are set up properly, and that you are loading
these files to a disk which has sufficient space available for the file(s).
Users with only floppy disks should make sure that each session starts with
a clean formatted disk in the download drive.

It can be a disaster to place all of your downloads in the same diredctory
as your communications program. Once you decide to clean it out, you stand
a good chance of deleting some of the programs along with the files you
no longer need.

Returning to the BACK YARD:

If you live in an older house, the phone wiring may be ancient. While good
for voice calls, it may be insufficient for data calls. Many BOC's offer
an inside maintenance service whereby they agree to maintain wiring inside
your house or apartment for X amount per month.
This doesn't mean that they will come in and re-wire the whole place, but
they WILL fix any problems. Unless you order a data line in many areas of
the country, MA BELL doesn't guarantee a perfect connection. Then if you
DO order a data line, a few filters are installed, and you get the bill
every month, normally paying the cost of the filters and labor in 2 months'
A house is one thing for access to wiring. Apartments often have problems
due to the way a builder may have installed things. The telco wiring code
for apartments requires that X amount of lines or "pairs" be provided
to each apartment. If one pair is bad, another can be used, or an extra
line installed as needed.
If you experience consistent connection problems with a modem, you may have
a wiring malady from your house to the phone company. It's a good idea to
have them check your lines if you suspect this may be the problem.

LINE NOISE in BOTH directions is usually an indication of a problem with
your line between the house and the exchange, or a problem within the
exchange itself.
There are still some old "stepper" or mechanical exchanges in some
areas of the country. Since the break-up of AT&T, there is no pressure for
a local BOC to upgrade. All they are bound to do is provide voice service.
These older exchanges can be a cause of constant headaches for modem users.

Calls from the OFFICE:

Another can of worms.........
You are now at the mercy of what your company uses for a communications
system. The local phone company is no longer involved (unless you are using
their equipment) once the wires or fibers connect to their terminal in your
If you are on a "Polling" system, you may get spurious line noise or
disconnects regularly. Some systems allow dedicated lines which are inde-
pendent of the regular system. These are the lines that normally work when
others will not due to system failure or a power interruption. Although
they may go through the same inter-office service, they have priority, and
are not subject to some restrictions.

Your company may be using a system which saves $$ by finding the cheapest
carier for a call. Most often, the least expensive carrier/path may be the
worst for a modem call. You can't control this one without a little hutspah.
THAT IS THE REASON you may call one time, get a bad connection, and then
get a great connection on the NEXT or third call, etc. It all depends on
what is going where, and from WHO, and to WHAT.

If you are calling from an extension that BEEPS you when someone else is
trying to call in, the same may happen. Then there's always someone
picking up the phone you may be using to call out. In an office
environment, the BEST bet is a dedicated line for modem use, or at least
a line you can control.
NOTE: Some newer internal systems compress "data" to a point where it
may be impossible to call out at a higher baud rate. The worst we have
heard is 1200 so far. Many LD services do the same during heavy traffic
times (per area).

Long Distance services and connections:

I don't want to fault US Sprint, but they make a good example.
I use them myself, and have found them to be good most of the time....
.............however........ saying that you're a "fiber optic network"
doesn't guarantee anything. NO long distance service can guarantee you'll
have the cleanest connection possible, because they can't guarantee
the lines you are using to get TO them. In one city, I can rig the line
in my hotel room to call out (many don't provide extra outlets or modular
connectors) and if the hotel's system is noisy, so is my connection....
... even with an MNP modem! Try again in 5 minutes.... perfect 9600 baud
connection! .......Why?....... The amount of traffic on many phone
exchanges dictates what type of connection you may get. That also accounts
for how loud and clear or faint & weak a voice call may be at any time.
Modems can't always HEAR things well either. If the connection is weak,
there's no telling what will happen.
NOTE: This can be a common problem, no matter WHO you use for a carrier.
Just like some office setups, carriers will go for X path first and if it's
tied up, they may opt for the next one, and it may be bad or good.
During off-hours, it's pot luck much of the time.

Even on LOCAL services, an exchange which may have problems may be
the cause of noise even if the surrounding exchanges are clean. If the
call must pass through a dirty exchange, the CLEANEST and BEST paths
on either end won't make much difference. These items are all additive,
and will certainly play on the quality of your call.


In Atlanta, just as other areas, phone connections sometimes get noisy
during high humidity (rain & murky weather). Corrosion on copper wires
tends to do its worst during these periods. In a few hours or days, these
problems go away. Again, it depends on where you are calling from or to,
and how well the local BOC is taking care of its hardware. It's almost
impossible to shield everything from the elements.

Normally, a solid complaint will bring action. If not, the user may have
other avenues.

In cases where a noise problem is found on a home line, it is normally
traced to a corroded wire or connection outside or in the path to the

Generally, all LOCAL calls are clean, unless a microwave link is involved.
Again, inclement weather may cause problems. Peak SUNSPOT activity tends
to disrupt MICROWAVE and SATELLITE transmissions, not to mention radio and
2-way comunications. Sunspots can send wide-band bursts of RF (Radio
Frequency) interference which will interupt almost any transmission.

Common Practice:

If you experience noise more often than not, have your phone lines
checked first. Next, check your modem and its setup for your COM program.

If you have trouble connecting to certain areas of the country, keep a
log of the trouble areas and contact your long distance supplier.

If you have CONSISTENT trouble connecting with one service or BBS in
a city, and no problem connecting with another service or BBS in the
SAME city (excepting locales where the area codes have been modified
for growth), leave a message to the service you have the most problems
with and let THEM check it out from their end. This only works well
where two services are within the same area code and city.

One phone exchange usually handles several prefixes.


You are at the computer in Oregon and decide to call Miami.
When you dial the number, it goes through the local exchange, to
a major area hub for MA BELL (BOC), then may be microwaved or sent via
satellite to a major hub on the other end.
When that hub gets the call, it routes it to the exchange which is
the home for the number you called.

This is a typical path, and you have gone through a lot of potential
problem areas:
Wiring to your exchange,
Wiring or microwave from the exchange to the hub.
Network traffic switching (depending on time of call).
Satellite or microwave from the hub to destination.
Destination hub to target exchange.
Target exchange to the modem you called.

Any number of things can happen on either end or in between.
Add switching of lines by vendors, carriers, local BOC quality control
and weather factors to that, and you have the formula for line noise.

(........"Local/National politics notwithstanding" ............)

From AV-Sync Atlanta (404) 320-6202

Both AT&T and the Public Sevice Commission have copies of this writing.

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