HP ProLiant 3000 Video Streaming Technology - Page 19

ECG068/0798 WHITE PAPER (cont.) 1...9 A standard HTTP web server sometimes acts as a "metaserver" that delivers the necessary URLs and information about the video content to the client for access. The video server often uses a different protocol called "Universal DataGram Protocol", or UDP, to provide the client with VCRlike controls and to provide a more "synchronous" data stream with less error-checking overhead than is done in HTTP. Internet Protocols As mentioned earlier, the time-critical nature of video makes it difficult to deliver in a normal way over packet-switched networks such as the Internet. For example, standard HTTP web servers using TCP/IP protocol are difficult to use for streaming video. Normal HTTP web pages do not support the 2-way interaction needed to control video streams such as dynamic bandwidth adjustment, rewind, pause, fast-forward, or indexing into the stream. In addition, the TCP/IP protocol adds additional overhead in the form of such things as re-transmissions in the case of missing packets that can be disruptive to a video stream. Most streaming video vendors therefore favor the use of dedicated video servers that use a unique protocol such as UDP (Universal DataGram) for video stream delivery combined with new real-time protocols that have been developed by the Internet Engineering Task Force (IETF) to support streaming multimedia such as video. IPV6 IP version 6 is a new Internet protocol intended to replace the current IPv4 in use around the world. IPv6 includes extensions for supporting multimedia data streams such as video. It supports multicasting, authentication/encryption, and a larger address space. Since it can't be rolled out everywhere at once, it is intended to be backward compatible with IPv4. MBONE The Multicast Backbone is an experimental overlay network on the Internet to gain experience with multicasting that will be supported in IPv6. There are approximately 1700 networks in 20 countries on the MBONE. It is currently being used for multimedia broadcasting such as radio shows and live concerts. UDP UDP stands for "Universal DataGram Protocol." Unlike TCP ("Transmission Control Protocol") it does not contain error-checked packets. Hence it avoids the overhead of re-transmission in the case of errors or lost packets. This is OK in streaming video as a few lost packets occasionally will not be noticeable to the eye. The disadvantage of UDP is that it does not penetrate most corporate firewalls. Several vendors have developed work-arounds for this. RTP RTP stands for "Real-Time Protocol." It is one of the most commonly used protocols for streaming media on the Internet. It adds a 10-byte header to UDP packets with information such as a time-stamp, sequence number, and type of compression, to enable the synchronized timing, sequencing, and decoding of packets at the destination. This enables multiple media streams such as video, audio, and graphics to be properly synchronized with each other as well as for the packets to be re-assembled in the right order at the receiving destination. Even though packets might arrive skewed by various degrees of network latencies, they can be reassembled and delivered with the timing and sequencing intended. RTP can also be used with other protocols such as TCP or IP Multicast.