A typical configuration would be that most of the time, computers would be connected wirelessly through one of a number of Network Address Translation (NAT) boxes that are connected to Broadband. Although a UPnP firmware upgrade may be needed for these units that will enable NAT traversal. This will enable use of all of the features of programs like Windows Messenger behind them. Voice and video instant messaging are dependant on this. When you wish to use the voice and video instant messaging real time communications (RTC) features, connect a computer directly to DSL and enable the Internet Connection Firewall for these sessions.

Windows Messenger version 4.0, which ships with Windows XP, as well as the updated Windows Messenger 4.7 that is now available, also include the ability to transfer files. However, by default, ICF blocks file transfer and you will need to manually configure the appropriate ports to open.

Here's how it's accomplished:

1. Click Settings on the Advanced tab of the Properties dialog box for your Internet connection, then click Add.
2. In the Service Settings window, type a description of the service.
3. Type the IP address or the computer name.
4. For Windows Messenger file transfer capabilities, the External and Internal Ports are the same and both are TCP. Use 6891 for both. If you wish to enable simultaneous transfer of up to 10 files, after clicking OK, set up additional ports in the same manner, numbering sequentially through 6900. You'll need 10 service entries total.

As shown in the image above, enable a single port only for a single file transfer only. The process to open ports to add other services is the same. Settings needed for some of the other more popular programs appear in the table below: