One of the neatest things you could do with an Internet connected computer is voice and video conferencing. For the price of a local telephone call to your ISP, you could circumvent the traditional long distance telephone network and carry on real-time live voice/video calls!

Windows XP takes voice and video conversations to the next level by leveraging two different technologies. You can use the old Microsoft voice/video conferencing stand-by, which is NetMeeting, or you can use the new kid on the block - the MSN Messenger. These two voice/video technologies work in different ways and have slightly different capabilities.

NetMeeting is installed on Windows XP, although you won't see it in the Start menu. You have to search the hard disk to find the conf.exe file and double click that file to get it started. NetMeeting uses a collection of networking protocols known as "H.323". The H.323 protocol "suite" allows you to do all sorts of things, including voice/video communication, instant messaging, file transfer, and application sharing.

The MSN messenger allows you to do the same things you can do with NetMeeting, but it uses a different set of protocols. The primary networking protocol is the Session Initiation Protocol (SIP). Although the MSN Messenger supports the same features as NetMeeting, the MSN Messenger does even more things, such as advanced noise cancellation (which prevents echoes from your speakers) and something called "presence awareness" so that you can find other users easily and make calls to them.

Both NetMeeting and the MSN Messenger work great if both the caller and the callee are directly connected to the Internet. When we say "directly connected" we mean that both computers are connected to their ISPs via a modem or network interface and both computers have a "public" IP address that is accessible to any computer on the Internet. When both computers are directly connected to the Internet, voice/video and data conversations are almost a no-brainer.

You'll run into problems if you want to have voice/video conversations when computers are behind a "NAT" device. Most DSL "routers" are NAT devices. The Windows XP Internet Connection Service (ICS) is also a NAT device. Most standalone firewalls used to protect home and business networks are also NAT devices. In order to use the MSN Messenger and NetMeeting behind a NAT device, you need something called an "Application Layer Gateway (ALG)". For the MSN Messenger, you need a SIP ALG, for NetMeeting you need an H.323 ALG.

There aren't too many places you'll find an H.323 ALG. Microsoft's premiere firewall, Internet Security and Acceleration Server (ISA Server) includes a high quality H.323 ALG. Setting it up can be a complex affair but once you get it going it works great! Many residential gateway manufacturers, like D-Link, are now including software that will allow you to use the MSN Messenger to make voice/video calls to other users. You can also use the Windows XP ICS as your residential gateway and it will handle MSN Messenger voice/video conversations for computers on the network behind it.