AV Technology - February/March 2009 - (Page 51) Video Source Network and decreases based primarily on the motion in the scene. Most internet-streamed content is delivered with TCP using the proprietary method invoked by the server. Examples include streams sent to Windows Media Player or to Adobe Flash Player. The server determines what type of video to stream, based on quality levels negotiated or preset by the player. The receiving player usually selects the bandwidth requirement and therefore determines the quality of the video transmitted. Over time, this technology is evolving to H.264 compression, which allows a wide variety of bandwidth/quality combinations. The stream can be created in as little as 64 kbps or use as much as 27 Mbps. Another important feature with this form of video is whether it is buffered and played, or stored and played at a later time. While there is a subtle difference, both involve downloading the video file to memory and playing it out. If the play out begins immediately, then the stream must be delivered in a smooth manner with enough throughput to keep the player busy. If it is to be played later, the transfer is similar to a conventional data file transfer and can use any reasonable period of time to be delivered. Layer 2 Network Switch(es) Video VLAN Voice/data VLAN ➤ VLANs created at layer 2 can be used to separate traffic by type. Voice, data and video may be separated with two VLANs as shown. Voice may also be segregated with a third VLAN. It is important to separate the bursty, broadcast data traffic from the video traffic. Note that computers might be on the video VLAN if they use a player that can read the video stream. tolerance for network jitter and will accept some latency in the network. It also has highly variable bandwidth requirements. The bottom line: no one network architecture fits all of these requirements. If the only type of video that will be on the network is internet-streamed video, then a separate network or VLAN is probably unnecessary. On the other hand, if the network is to carry primarily conventional video, separat- THE NETWORK ARCHITECTURE FOR VIDEO Conventional video transported across an IP network allows very little network jitter (“burstiness” causing variable delay). It also requires uniform bandwidth. Videoconferencing must have low network latency, but has moderate tolerance for network jitter. Internet streaming video has a high http://www.doremilabs.com
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