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Improving modem throughput speeds

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Improving modem throughput speeds

If you have a 33.6 kilobits per second (Kbps) (V.34 protocol) modem and consistently connect at 26 Kbps or higher, or you have a 56 Kbps (V.90, K56flex, or X2 protocols) modem and consistently receive data from your Internet service provider or online provider at 40,000 bps or higher, there is not much you can do to go faster. Higher speeds are not possible with most phone circuits. The rated speeds are only possible with a near-perfect connection.

If you consistently connect at slower speeds (24 Kbps or less for a 33.6 Kbps modem or less than 40 Kbps for a 56 Kbps modem), you can try the following:

  • Check that the correct manufacturer and model are listed for your modem in Phone and Modem Options. If your modem is not listed correctly, try following the steps in Install an unsupported modem to install the correct modem.

  • Check if the manufacturer has a new installation disk or .inf file available. Files can often be downloaded from a manufacturer's Web site or bulletin board.

  • For a 33.6 Kbps modem, make sure the Maximum Port Speed is set at 38,400 bps or higher (57,600 is recommended). For a 56 Kbps modem make sure it is set at 115,200 bps. See Change the maximum modem port speed for instructions.

  • Make sure the modem is operating at the correct temperature. Most modems operate better if they do not get too hot or too cold. Do not block air flow by placing things on top, under, or around your modem or computer.

  • Try connecting to numbers that you know support a given speed. This lets you know whether the problem is at your end or the other end.

  • Make sure a local number is actually a local call. Many online service providers forward local calls to a distant location to provide local calling service. This works well at 14,400 bps, but can degrade the signal and limit higher speeds.

  • If your phone line has a surge protector, you can try using your modem without it. Note, however, that doing so eliminates the protection provided to your equipment by the surge protector.

  • Have an expert check the telephone wiring between the telephone company connection and your computer. Faulty wiring, soldered connections, long connecting cables, inferior equipment (phones, fax machines, or even other modems) can all degrade the signal. To distinguish between wiring and line problems, check the voice quality, both while the local wiring is connected and on the telephone company line while it is disconnected from the local wiring. Many phone companies now connect their service with a modular plug, which consumers can disconnect to perform this check.

Telephone companies normally do not guarantee data throughput speeds. When you ask your telephone company to fix a noisy line, you may be told you need a data line or conditioned circuit. This is usually an expensive solution. Modems can perform well on a good quality voice circuit. Ideally you want your system tested with a sophisticated line tester (a "bit error rate tester" or "data test set") rather than the regular line tester. You can also ask the company to switch you to a different cable pair from the central office. Sometimes, people solve the problem by ordering a different phone number.

For additional information, see Attaining fast speeds with a 56 Kbps modem, Data transfer speed, and Optimizing data transfer speed

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