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We frequently hear comments from our users that "My modem is a 28.8 or 33.6 or 56K model and I'm only connecting at x (some speed slower than the maximum). Why is this?" Well, here is the explanation as we understand it:

Modems are able to communicate at a variety of speeds in addition to their maximum speed. Not only is this done to provide compatibility with slower modems, it allows two modems to communicate under less than ideal circumstances. If, for example, a particular telephone connection is noisy, two modems will probably not be able to communicate at their highest speed. But rather than not communicate at all, the two modems will very quickly run a series of tests on the telephone line to determine if they can communicate reliably at a slower speed. If so, they will connect at the fastest speed that can be maintained under the current conditions. Listed below are the standard speeds that a 33.6 or 56K modem may connect at:

33.6 Modems or Slower Additional 56K Modem Speeds
300 bytes per second 33333 bytes per second
1200 bps 37333 bps
2400 bps 41333 bps
4800 bps 42666 bps
7200 bps 44000 bps
9600 bps 45333 bps
12000 bps 46666 bps
14400 bps 48000 bps
16800 bps 49333 bps
19200 bps 50666 bps
21600 bps 52000 bps
24000 bps 53333 bps
26400 bps 54666 bps
28800 bps 56000 bps
31200 bps 57333 bps
33600 bps 64000 bps

This list applies to virtually any modem currently in use. It is not possible, of course, to have a 28.8 modem connect any faster than 28,800 bps and likewise for a 14.4 modem at 14,400 bps.

So, now that we know it is not unusual for a modem to connect at less than maximum speed, what can cause this to happen? Here is a list of some of the things that can slow you down:

Now, if this isn't bad enough, we should also consider how the computer software (in this example, Microsoft Windows) reports modem connection speeds. When a modem connects, the incoming and outgoing speeds are not necessarily the same. If the speeds differ, the incoming speed will usually be the faster of the two (which is desirable for surfing the Internet). However, when Windows reports "Connected at x bps" it chooses to report the slowest of the two speeds. What you see on-screen should generally be considered the worst case scenario.

Thus far, everything that we have discussed has been contrary to establishing a fast connection. Now for the good news! 28.8 and faster modems can not only negotiate to slow down but they can also negotiate to speed up. These modems constantly monitor line conditions to give the fastest rate that the current connection can support. Windows will not report any increase or decrease in speed to you (the "Connected at x bps" message never changes) but you might notice some difference in the "feel" of a connection that was reportedly slow to begin with. Of course, with all of the variation in Internet traffic patterns and individual web sites, this may be difficult to determine. If you happen to establish a connection that is reported as being slower than what the modem is capable of, be aware that the speed may increase or decrease many times during a session.

Hopefully this discussion will provide some idea of the complexity and variability involved with modem communications. If you have further questions or comments about this topic, please contact us.