Streaming protocols
The big breakthrough that enabled the streaming revolution was the adoption of a new Internet protocol called the User Datagram Protocol (UDP)
and new encoding techniques that compressed audio files into extremely small packets of data. UDP made streaming media feasible by transmitting data more efficiently than previous protocols from the host server over the Internet to the client player or end listener. More recent protocols such as the RealTime Streaming Protocol (RTSP) are making the transmission of data even more efficient.
UDP and RTSP are ideal for audio broadcasting since they place a high priority on continuous streaming rather than on absolute document security. Unlike TCP and HTTP transmission, when a UDP audio packet drops out, the server keeps sending information, causing only a brief glitch instead of a huge gap of silence. TCP, on the other hand, keeps trying to resend the lost packet before sending anything further, causing greater delays and breakups in the audio broadcast.
Prior to UDP and RTSP transmission, data was sent over the Web primarily via TCP and HTTP. TCP transmission, in contrast to UDP and RTSP transmission, is designed to reliably transfer text documents, email, and HTML web pages over the Internet while enforcing maximum reliability and data integrity rather than timeliness. Since HTTP transmission is based on TCP, it is also not well-suited for transmitting multimedia presentations that rely on time-based operation or for large-scale broadcasting.
Later in the chapter, you will learn why protocols are important. Some streaming technologies such as RealAudio and Windows Media utilize dedicated servers that support superior UDP and RTSP transmission. Other formats such as Shockwave, Flash, MIDI, QuickTime, and Beatnik are primarily designed to stream from a standard HTTP web server. While these formats are cheaper and often easier to use since they do not require the installation of a new server, they are typically not used in professional broadcasting situations that require the delivery of hundreds or thousands of simultaneous streams.
HTTP streaming is thus referred to as pseudo-streaming, since technically it is possible to stream via HTTP. But it is much more likely to cause major packet drop-outs, and it cannot deliver nearly the same amount of streams as UDP and RTSP transmission. Herein lies the difference between most low-end solutions and more professional broadcasting solutions that require dedicated servers and extra bandwidth and server capacity.
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