H.323 is a standard for VOIP. It was originally developed to allow video conferencing network traffic to be carried over IP, but it rapidly was co-opted into the VOICE over IP movement. It really allowed voice over IP to happen. At this point, h.323 has to be in a network that wants to deploy/use voip phones. It's often used in conjunction with a QoS environment, because the H323 uses UDP, not TCP, and is therefore a 'best effort' delivery. THe network has to provide an environment that prevents packet loss or jitter...and that's what QOS is about