28,800bps Connection FAQs
Q: Why can't
I connect at 28.8?
A: Most phone companies only support
data speeds of 14.4 or lower, even though it is most likely that it will
go faster. A typical phone line is compressed at the switch using ADPCM
and routed through miles and miles and miles of cable, causing the line
quality and signal to diminish. If you are connecting at a rate of 21.6,
or above, this is normal.
If you consistently connect at 26,400bps or above, consider yourself
fortunate -- it's almost impossible to go faster than that on many phone
circuits. This is not false modem advertising -- 28,800bps modems are designed
to wring as much speed out of the actual real-world connection as possible,
and 28,800 speed is only possible on a near-perfect connection.
Q: What can I
do to ensure maximum speeds?
A: Even if you consistently connect
at lower speeds (e.g., 24,000 or even 21,600), there may be little you
can do, but you can at least try the following:
- Make sure that your serial port is locked at 38400 or higher (57600 recommended). This is usually set within your comm application, not the Windows Control Panel.
- Try connecting to known 28800 numbers (e.g., Hayes at 800-US-HAYES; Multi-Tech at 800-392-2432; USR at 708-982-5092). This will at least tell you whether the problem is at your end or the other end of the connection. (The USR number is particularly useful, because you can get an on-line reading of connection quality from a USR BBS command.)
- If possible, test for premises problems by disconnecting all your premises wiring (and equipment) from the incoming telco terminating block, and hooking your modem directly to it. If your connections are better, you have a premises problem that you may be able to isolate and fix. Premises problems (faulty wiring and/or equipment -- i.e., phones and fax machines) are a frequent cause of 28800 connection problems.
- Listen carefully to the quality of your voice connections. Note that you must dial a known quiet number, since many otherwise good phone lines exhibit excessive noise until you actually connect. (Dialing a single digit is not enough.) After you connect, if you hear more than very faint hiss and/or hum, then you probably have a line problem.
- While a quiet line is important, there are other line problems that can reduce your speed: bandwidth (frequency response), distortion, etc. It is difficult to test for these problems without proper test equipment, but it's still a good idea to listen carefully for audible problems, particularly if you can find a number that will send you test tones.
- You may be able to get your phone company to improve the quality of your line. Since phone companies are often reluctant or even unwilling to work on data problems, it may help to report that you are also having fax problems. Or you can try asking for a data or fax "specialist". Ideally, you want the service technician to bring the right kind of equipment, a sophisticated line or transmission test set, not just the normal best tester. It may also help to ask for a BERT (bit error rate tester) or "data test set." Note that the phone company may charger for these services.
- Sometimes, switching to a different cable pair from the CO (central office) will help.
- You may be told that you need a special "data" line, more properly called a "conditioned" circuit, which is considerably more expensive than a standard "voice-grade" circuit. This is usually isn't necessary - all you generally need is a good quality "voice-grade" circuit.
- Add-on noise filters will not help. Your 28,800 modem already has all the filtering it can use. An add-on filter will do nothing at best, and it may make things worse.