You have a modem that does not connect at the maximum speed for which it is rated. For example, you have a 33.6 KB modem that usually connects at a speed like 28800 baud or 26400.
This is usually normal, although there are various factors that can influence the connect speed of the modem.
The main reason why a modem will usually not connect at its maximum theoretical speed is line quality; as modem speeds get faster and faster, they are more likely to only reach their top rated speed under ideal conditions. While a 14.4 KB modem will usually actually connect at 14400, a 28.8 KB modem will only hit that speed for some people, and for others only some of the time. Many people get only 28800 on 33.6 KB modems (like me). 57.6 KB modems are very deceiving in terms of how they are named, because nobody can really get a 57600 connection from one of these today.
In general, if you are getting 24000 or better from a 28.8 KB or higher speed modem, that is usually considered normal.
There is probably not a lot that you can do to substantially change this, assuming that there isn't some other problem involved, and by itself it does not mean that your modem is defective (although a 57.6 KB modem that is this slow would make me raise an eyebrow). I have a 33.6 KB modem that has never connected to my internet service provider above 28800. Here are some ideas of things you can try to improve your connection speed and/or verify that there really isn't an actual problem that is causing the slow connections:
1. Try dialing some different numbers and watch the connection speeds. You may find that the slow connections are due to the host you are dialing into. Make sure that if you are using a 57.6 KB modem that the host you are dialing into supports it, or you will see no benefit.
2. Listen for a hum or ring on the line by dialing a number with a voice phone and listening closely. You should actually complete a call, not just dial a number on the phone. If you hear an audible hum or ring then your phone line quality is suspect.
3. Try using a different wall jack in the building you are in. It is possible that you may get better results this way, but realize that there is some random variation involved, so don't just try each jack only once.
4. Try disconnecting your modem from any surge suppressors that you may be running through. These can sometimes cause interference (but read here about the risks of running without this protection.)
5. Try contacting your modem manufacturer's technical support department if you suspect a problem with your modem that is causing significantly slower connections than should be normal (but don't be surprised if they tell you that there is nothing you really can do).
NOTE: The information above is from The PC Guide(We have edited some of the content).
A great modem trouble shooting resource can be found here