How to improve the Connect speed of 28800 modems . . . If you rarely get 26.4 kbps or 28.8 connects, the reason is almost always a result of phone line quality. 28.8/33.6 modems are pushing the limits of today's telephone system. Getting 28,800 bps connections requires pristine telephone line conditions end-to-end. The following three paragraphs, which are from a paper entitled Of Line noise, The Phone Company, and Your Modem by Patrick Moore, Supra Corp., explain this in more detail:
- Repeatable results with V.FC/V.34 modems on real-world phone
lines are sometimes difficult to obtain. Unlike V32.bis modems,
V.FC/V.34 modems will actually modify their data coding (symbol
rate) and transmit levels during the connect phase. Very minor
differences in the phone line can lead to quite different results.
- A 28.8K connection on some real-world lines may not occur very
often, if it occurs at all. Preliminary testing in the lab
indicates that "normal" phone line attenuation makes a 28.8K
connection difficult even in the absence of line noise. This is
not surprising considering that the V.FC & V.34 coding schemes are
relying on the bandwidth of the phone system being greater than
what is actually available in some areas. Very high-speed
connections assume that there is a substantial amount of digital
technology in the system (thereby normally increasing the usable
bandwidth). Some users are going to find that their local phone
system effectively limits them to 16.8K or 19.2K.
- Both the originating and the answering modem are adjusting to
their line conditions during the connect phase. The fact that
a connection to a given modem at a given location occurs at a
lower rate (19.2k for example) may have nothing to do with the
modem the call is placed with, or the location it is placed from,
as the modem on the other end may be adjusting the baud rate down.
For the above reasons, many people will never see 28.8 or even 26.4 CONNECTS with their 28.8 modem. The easiest way to find out if its your phone line or your modem is to find someone who usually gets 26.4 or 28.8 connects, and try your modem on her system, or his modem on your system. You will most likely find that the problem at your end is phone-line related.
The part of the telephone system which you may be most able to improve is your telephone premises wiring. If you rarely get 28.8 or 26.4 connects, try the following:
- Premises Wiring . . . Often faulty premises wiring, bad phone jacks and plugs, cheap phones, old/antique phones, or too many phones or other devices cause problems. Here is how to determine if your premises wiring or equipment is affecting your CONNECT quality. Find the telco wiring block where all your premises wiring connects -- it will usually be outside or inside of your house near where the phone line comes in. Look at the interior wiring. The best wiring is "twisted pair". Most older, non-twisted pair wiring consists of four wires in a single jacket. The individual wires have solid color insulation (green, red, yellow and black -- but only the green and red wires are normally used on a single-line system). Twisted pair wiring consists of matched pairs of wires, normally 2 or 3 pairs in a single jacket. The two wires in each pair are twisted around each other in a gentle spiral. Of each pair, one wire has a colored insulation with a white stripe, and its mate is white with a matching colored stripe (i.e. white with blue stripe and blue with white stripe).
If you have non-twisted pair wiring, you should consider replacing it. But whether you have twisted pair or not, you may want to try this experiment. Run a good quality twisted pair phone cable directly between the block and the phone jack that serves your modem, routing so as to avoid other electrical wiring and devices -- and then disconnect all other premises wiring from the telco block. If this gives you faster connects, then your premises wiring or your phone equipment is causing you trouble. Reconnect wiring and phone devices incrementally while retrying the modem to see if you can find the culprit. Examine each plug and jack, and reseat each several times. Where visible, inspect the routing of the phone wiring to assure it steers clear of other wiring and electrical devices. If you find some of your equipment or premises wiring is contributing to the problem, the recommended solution is to replace or eliminate the equipment and/or wiring. However, read on for one alternative solution.
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- Telephone Co. Line Quality . . . If you determine that your premises wiring is not causing problems, and you still get low connect speeds, you can try a few other things like calling a known quiet number and listening carefully -- if you hear hissing, humming, a radio station or other background voices, you have a line problem (you may have a line problem even if the line sounds quiet). Reporting noisy conditions will probably be sufficient to get the phone company to look into the "problem". You may be able to get them to test and improve your line, but be aware that all they guarantee to provide is a line meeting voice quality standards, and also they may want to charge you for the testing if they find no line problem. So you telling them your modem can't get 28.8 connections probably won't motivate them. However, it has been reported that the phone company will generally be responsive to fax problems, so report those if you have them. Your connect speeds will frequently be lower when you are distant from your telephone exchange , and when your call must pass through more than one exchange. See the The Navas FAQ for a more detailed discussion about line problems.
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