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A common misconception among computer users is that the telephone company and long-distance switching network is a "perfect system." The advent of error-correcting, high-speed modems which mask line-noise and push the data transfer tolerance window to the limit, has given us a false sense of belief that everything should work at top speed every time.
Not so! There is that age old problem known as LINE NOISE. Line noise may or may not be apparent to your "naked ear", however your modem can and will react to this annoying phenomenon. Some caller complaints which can be attributed to line noise are:
"The system was very slow in responding tonight."
"What I typed didn't show up on the screen until two words later."
"I'm was only getting #### CPS, what's the matter with your system?
"When I downloaded 156K of the 175K file you dropped carrier on me."
These problems in data signal transmission and recognition can take many forms. The callers quoted above complained of slow system response, buffered typing response and slow transfers. They were certain it was a problem on the ISPs system. What was the reason? Best guess is a lousy connection most likely with excessive line noise.
If you have line noise or any other problem with a modem connecting to your ISP, you should have your equipment or telephone line checked.
What can you do when you experience modem-related difficulty?
1. Remove all other connections to your telephone line (answering machine, fax, extension phones).
2. Use a short, shielded serial cable.
3. Increase your modem's "time-to-drop-carrier" by adding S10=20 to your setup or initialization string.
4. Have your line checked by the phone company.
To have your line checked by the telephone company, call the local business office. Provide your name and telephone number. Tell the telephone company representative you have noise on your telephone line. Some telephone company representatives may not be helpful, claiming that they have no obligation to provide line quality sufficient for modem communications. Here is some information which might prove to be very helpful.
MINIMUM LINE TESTING REQUIREMENTS
AS SET BY THE FCC, your local telephone company is required by the FCC to provide a minimum level of quality on the lines it maintains for your use. Many lines do not meet these standards, and so are a source of considerable noise in the transfer of data between computers.
The telephone company may tell you there is usually only one option offered: line conditioning (at $170/line!!). This is an extra cost item that they would like to sell you. However, if their line to your computer meets the minimum standards, there is no reason you cannot have error free transfers if an error correcting protocol is used. If the telephone company seems reluctant to test your line and assures you that it meets the minimum requirements, request that they perform POTS Data Testing and provide you with the results. Let them understand that if they do not comply, you will refer the matter to the FCC. They will NOT be happy!
The POTS Data Testing involves the following tests:
1) Frequency sweep 300 to 3000 Hz
2) Roll off 500 to 2500 Hz with -2 to +8 range
Request 300 to 3000 Hz with -3 to +12 range
1000 Hz tone loss -16, 1% in either direction
3) Signal to noise ratio 24 Db level
4) White noise C message Dbrnco
5) Envelope delay measurement
6) Phase jitter not to exceed 10%
7) Impulse noise test minimum 15 minute count
Don't worry if you do not understand what all these tests mean, the telephone company knows. These standards are all available from the FCC upon request. When the lines provided to you meet these minimums, you will experience reliable, accurate, and noise free data transfers.
The Hardware Setup:
Your modem is a modulator-demodulator device. It converts digital signals (bits) sent by your computer's serial port to analog signals which can be transmitted over telephone networks. Purchase the highest quality modem you can afford. If you have an internal modem, you don't have to worry about why motherboard and serial card manufacturers are still designing equipment that won't support high-speed modems. If you have an external modem, then your computer serial port if like most, came to you with a slow UART chip which would work fine with 300, 1200, 2400 and 9600 baud modems. Almost every computer shipped (even today when everyone knows better) has this old slow chip. If you have a fast (V.32/V.32bis/HST/V.34/V.42/V.90) modem, and are experiencing dropped characters, CRC errors and aborted downloads, upgrade your serial port to a buffered UART (16550AFN). Look for 82x50B, 16x450 part numbers on the large 40-pin chips on the serial card to find out if your UART is the out-of-date device.
The Software Setup:
Most of you use the Dial-Up Networking provided as part of Windows or the MAC operating system. These normally install correctly and thus work fine. Some of you use older versions of the operating systems and thus require additional software to make connections to us. Generally, all communications with the ISP have these common factors for connection:
Dialing parameters: 8 DataBits, N (no) Parity, 1 - Stop Bits
Maximum Speed: set for highest recommended by manufacturer (generally 57600 for 14,400 modems, 115200 all faster modems). Special note here: Make sure your com port is set up to match this otherwise this is a bottleneck.
Generally scripting is not required for PPP connections.
Flow Control: Software (XON/XOFF) for older modems (14.4 Kbps and lower), Hardware (CTS/RTS) for high-speed modems (above 14.4 Kbps),
If you have the call-waiting service on your telephone line, you MUST disable it before each modem call or you risk having your connection interrupted. Call waiting is disabled with Ameritech if you dial "*70" before the telephone number. For GTE it is disabled if you dial '70# before the telephone number. The place for this is in the "dialing prefix" in your telecommunications software. If that is not available in your software, you can add this information in your dialing directory.
Believe it or not, rainy days and ice storms can affect telecommunications.
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