ARCHIVED: What is flow control, and how do I set my modem to use it?

If your modem runs at 2400 bps or faster, and has built-in error correction and data compression, then something must control the flow of data between your modem and your computer. Whether hardware- or software-based, flow control is what prevents your computer from being flooded with too much data too fast.

Software flow control is called XON/XOFF; hardware flow control is called RTS/CTS Control (Ready to Send/Clear to Send). You can use your communications program to set both kinds of flow control (you can usually find the flow control options in the Setup menu). You can also use the instructions below to set flow control in Windows.

If your modem is fast enough to need flow control, use RTS/CTS. XON/XOFF sometimes injects unwanted characters into binary files as you upload or download them, so you should use it only when communicating with another computer that demands it.

Windows XP and 2000

Follow the instructions below to change your flow control settings:

1. From the Start menu or the desktop, right-click the My Computer icon and select Properties.
2. In the Properties window, click the Hardware tab, and then Device Manager....
3. In the Device Manager window, click the + (plus sign) next to Modems. Right-click your modem, and then select Properties.
4. In the Properties window, click the Advanced tab and then click Change Default Preferences....
5. You should now see a list of several options. Flow control should be the last option in the list. Configure it as you wish.