The fact that an ISDN connection has two channels (B-channels) makes it possible to connect to the Internet twice as fast. All it takes is establishing a so-called "multilink" connection to your Internet provider, which may let you reach transfer rates of up to 128kb. The downside is that charges will accordingly be twice as high. Plus, not every provider offers multilink connections! Therefore, you can either consult your provider or just give it a try.
In principle, all recent Windows versions with the exception of Win 95 are capable of creating multilink connections via dialup. If you are running Windows 95, make sure to install the Microsoft Accelerator Pack 1.1, which updates the Dial-Up Network and enables multilinking. Please note that this update is already included in Windows95 versions V 950.b and higher!
The full cFos installation guide can be found here.
Make sure to select two COM ports during installation (e.g., COM4 and COM5)!
After installing, select [Start] [Settings] [Control Panel] and go to the [Modem manager] entry. Add a new modem (cf. Installing a Modem).
Install the "cFos ISDN, Internet, Sync PPP over HDLC" modem to COM4 (cFos Port 4), then add the "cFos ISDN, 2nd Sync PPP over HDLC" modem and assign it to COM5 (cFos Port 5).
Select an existing DUN connection or create a new one. Right-click on that connection and select its [Properties].
Win95: Click on [Settings]. Check the "Additional devices" option and [Add] the "cFos ISDN, 2nd PPP-Modem."
Win 98: Take note of the "Multilink" option and check "Use additional devices." Click [Add] and select the "cFos ISDN, 2nd Sync PPP over HDLC" modem from the list.
Win ME: Take note of the "Multilink" option and check "Use additional devices." Click [Add] and select the "cFos ISDN, 2nd Sync PPP over HDLC" modem from the list.
Win2000/XP: Check the devices you wish to use for connecting under the properties of each respective DUN connection. (The "Options" tab under "Additional devices" will let you adjust a number of additional dial-in settings.)
After successful dialup, the second channel is added automatically to an active DUN connection.
Once both channels are open, right-clicking on the connection icon will display the connection status.
This is also where you can find the "Activate/Deactivate additional devices" option under [Details]. If only one channel is needed, the second channel can be closed down by clicking on [Deactivate]. If necessary, it can be brought back up at any time by clicking on [Activate].
Remember that you can find out whether one or both channels are currently in use simply by looking at the cFos skins or status window.
By default, the "cFos ISDN, 2nd Sync PPP over HDLC" modem will block any connection during the first 7 seconds. If necessary, that connection can still be activated manually in the DUN. You can deactivate this setting with register S75.9=0.
If a call is coming in while a multilink connection on both ISDN channels is still active, one channel will be shut down automatically. You can deactivate this by setting S74.12=0.