Audio and video live streaming – This class of applications is similar to traditional broadcast radio and television transmission emitted from any corner or the world. Since streaming live audio/video is not stored, a client cannot fast-forward through the media. However, with local storage of received data, other interactive operations such as pausing and rewinding through live multimedia transmissions are possible in some applications. Live, broadcast-like applications often have many clients who are receiving the same audio/video program. Distribution of live audio/video to many receivers can be efficiently accomplished using the IP multi-casting techniques.
However, live audio/video distribution is more often accomplished through multiple separate uni-cast streams. As with streaming stored multimedia, although the timing constraints are less stringent than for real-time interactive applications. Delays of up to tens of seconds from hen the user requests the delivery/play out of a live transmission to when play out begins can be tolerated.
Real- time interactive audio and video
This class of applications allows people to use audio/video to communicate with each other in real time. Real time interactive audio over the internet is often referred to as internet phone, since, from the user’s perspective, it is similar to the traditional circuit-switched telephone service. Internet phone can potentially provide PBX (private branch exchange), local, and long-distance telephone service at very low cost. It can also facilitate the deployment of new services that are not easily supported by the traditional circuit-switched networks, including Web-phone integration, group real time communication, directory services, caller filtering, and more. There are hundreds of internet telephone products currently PC-to-phone and PC-to-PC voice calls.
With real time interactive video, also called video conferencing, individuals communicate visually as well as orally. There are also many real-time interactive video products currently available for the internet, including Microsoft’s Net-meeting. Note that in real time interactive audio/video application, a user can speak or move at any time. For a conversation with interaction among multiple speakers, the delay from when a user speaks or moves until the action is manifested at the receiving hosts should be less than a few hundred milliseconds. For voice, delays smaller than 150 milliseconds are not perceived by a human listener, delays between 150 and 400 milliseconds can be acceptable, and delays exceeding 400 milliseconds can result in frustrating, if not completely unintelligible, voice conversations.