Optimizing data transfer speed

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

Optimizing data transfer speed

The speed settings for a modem are usually set correctly during installation. There are two different speeds set in Phone and Modem Options: Maximum Port Speed in the general modem properties and Port Speed in the default preferences. Both of these specify the speed at which communication programs send data to the modem, not the speed at which data is transferred between your modem and the remote modem.

The Maximum Port Speed specifies the maximum speed programs can transmit data to a modem. Most programs set their own speed, so this limits the speed at which they can send data. The Port Speed is the current port speed for the modem. These two settings are usually the same, although there are some instances in which one should be changed. Do not change these speeds just to match the rated speed for your modem.

Measuring your modem speed

There are several separate components that determine the speed of the connection. When a program or hardware reports transmission speeds, note carefully what is being reported. For example, if a V.34 modem rated at 33.6 kilobits per second (Kbps) reports a connection speed of 38.4 Kbps or higher, it is reporting the port speed that data is transmitted from the computer to the modem rather than the rate that data is transmitted between modems.

For practical purposes, you want to know the throughput speed, the speed that your data is transferred between your communications program and the program on another computer. Communications programs usually report the throughput speed and normally provide the speed in either bits per second (bps) or characters per second (cps). For serial communications, speed in bits per second can be divided by 10 to approximate the characters transmitted per second.

Check the throughput speed after you start communicating with the remote computer. The initial throughput speed is not necessarily a good estimate of the transmission speed. Modems often shift speed up or slow down after the initial connection. Modems can fall forward or fall back depending on the quality of the connection and other factors.

Transmission speeds for direct serial connections

When you create a direct serial connection to another computer or device, you may need to adjust the maximum port speed for the connection. The initial setting for a direct serial connection is 19.2 Kbps. For a Windows CE device or other device that supports higher data transmission speeds, change the maximum port speed to the correct speed. Refer to the manufacturer's instructions for the transmission speed supported by the device.

For additional information, see Attaining fast speeds with a 56 Kbps modem, Data transfer speed, Improving modem throughput speeds, Change data connection preferences, or Change the maximum modem port speed.