Network Video Overview 03/10/04

Networked video services can be broken down into two major categories:

Interactive and Non-Interactive.  

Interactive Video
Interactive networked video provides the ability for participants at two or more locations to see and hear each other in real time.  Videoconferencing is the form of interactive video with which most people are familiar.  Three technologies are utilized to provide interactive video services across a network -- broadcast quality, traditional videoconferencing, and desktop videoconferencing.
Broadcast quality

Very high quality, interactive video and audio can be delivered across a network by utilizing MPEG-2 compression & decompression (codec).   Very often this method is used when access to production recording and broadcast facilities is desired.  Multipoint interactive conferences can be held if the codec supports simultaneous decoding of multiple MPEG-2 transmission streams.  Since MPEG-2 utilizes 3Mbps - 15Mbps of bandwidth, these video services are restricted to high performance networks (i.e. TTUnet campus network, vBNS, Internet2, etc.).
Traditional videoconferencing (ITV)

Typical interactive video has employed the use of compressed  (H.320) video and audio for years. Developed for use on telecommunications networks, H.320 videoconferencing is deployed over ISDN PRI or leased T1 lines.  Circuit emulation techniques allow these PRI/T1 lines to be extended over the existing fiber optic infrastructure to campus buildings and interconnected with long distance T1 lines.  H.320 videoconferencing provides dial-on-demand or pre-scheduled meetings and multi-site conferences.
Desktop videoconferencing

The desire to extend videoconferencing capabilities beyond class rooms and conference rooms to the desktop has led to the development of the H.323 standard for networked videoconferencing.  Although not as mature as traditional (H.320) methods, desktop videoconferencing may provide a more scalable means of providing interactive video services for individual participation.   A wide range of desktop solutions is available which vary in price and performance.  A complete networked solution for desktop videoconferencing will provide gateway services between the desktop systems and the traditional (H.320) systems.

Non-Interactive Video
As the term implies, non-interactive video is the one-way transmission of archived video clips or live events with no end-user participation.  This form of video is most commonly provided by a high-end video server which contains the archived video and/or has the ability to broadcast video at predetermined times.  The two technologies typically used to deliver video from the server to the client system are video streaming and multicasting.
 Video streaming

Video streaming is characterized by its on-demand availability.  Each individual client computer initiates an independent stream of video from the server to client software.  This allows the client to pause, fast forward, backup, etc. much like a virtual VCR.  Since each client receives its own stream of video, network bandwidth is consumed rapidly under heavy utilization.

 Video multicasting

Video multicasting is very much like pay-per-view television.  At predetermined times of the day, video program content is "broadcast" across the network.  Client software "tunes in" to the broadcast and views the video in real time.  Video multicasting is also often used for live broadcasts of events.  Multicasting of video consumes far less bandwidth than video streaming.