HP ProLiant 3000 Video Streaming Technology - Page 16

ECG068/0798 WHITE PAPER (cont.) 1...6 Quality of Service (QoS)-As mentioned earlier, video streaming works best when there is continuous availability of sufficiently high bandwidth in the communications channel. This is especially important for time-critical applications such as video and audio. Variable video/audio packet delays can cause picture jitter and annoying audio starts and stops. To evaluate this for different networks, a new measure of network capability has emerged known as Quality of Service (QoS). Good QoS provides a guaranteed bandwidth at a constant small delay or latency even under congested conditions. Dedicated connections provide the best QoS. Shared media technologies such as Ethernet or the public Internet exhibit variable packet data delays that can play havoc with multimedia data such as video and audio. Specialized protocols and methods have been developed to provide better QoS over these networks. Support for Multicasting-Another important characteristic for transmission of video over a network is the ability to support multicasting, broadcasting, and unicasting of video streams. Multicasting lies between broadcasting and unicasting. Unicasting delivers streams 1-to-1 to each client, and is sometimes referred to as "Video-onDemand" (VoD) since any user can request any stream at any time. Unicasting separate video streams for each client consumes a lot of network bandwidth. Server Router V1 V2 V3 Network Router Unicasting Multicasting, by contrast, delivers streams simultaneously 1-to-many clients where the clients are typically on a subnet of the network. Multicasting is sometimes referred to as "Near-Video-onDemand" (NVoD) since the subset of users must view the same content at the same time. This is similar to cable TV "pay-for-view" where a subset of users must be authorized to view the program. Applications might include such things as having a subset of users who are all signed up for the same training course. However, there can also be multiple subsets of users viewing different multicasts at the same time.. Multicasting one video stream serving several clients conserves network bandwidth. V1 V V2 Server Router Network V3 Multicast Router Multicasting