Web broadcasting is the use of the Internet to send content, via a dedicated stream of data, to anyone who tunes in to that particular continuous flow of sound, video, animation, or combination thereof. Webcasts are usually live broadcasts of content as it is being "pushed" or "streamed" to users. Streaming of data is a useful technology because it takes into consideration that different users are not able to access the same data stream via the same quality of Internet connection. When you normally access a web page or a file on the Internet, your browser is connecting to a host server or another computer which stores that file. Your machine "grabs" the content from that server and brings it up in your browser window or downloads it to your hard drive. If it is a large enough file, it might take forever to download. With streaming media and webcasts, the content is being "pushed" or "streamed" to your browser as soon as your browser accesses the content. Depending upon the type of machine you are using and the speed of your Internet connection, you can basically play the content before it has finished the download from the server you are trying to access. To enjoy streaming media content, you need a computer with a fairly decent video card, sound card, speakers, and a streaming media player, which is software that operates through your web browser. Popular examples include RealNetwork's RealSystem G2, Microsoft Windows Media Technologies, and VDO's LivePlayer. The World Wide Web Consortium (W3C), the body that develops standards for the Web, introduced a markup language for streaming media Synchronized Multimedia Integration Language (SMIL). SMIL resembles Hypertext Markup Language (HTML) used for Web documents, but it lets Web developers decide how to code multimedia in Web documents. The idea behind SMIL is that developers can divide multimedia content into individual streams and files that can be displayed individually or as a single stream through the end user's machine, making multimedia documents smaller and faster to access. This is possible because SMIL is derived from XML (eXtensible Markup Language), which defines the commands that manipulate content, instead of defining the actual content elements. SMIL is not a competitor to other media formats, but it does offer the ability to join different media formats and types of content in efficient ways. Maybe you have already experienced streaming media of one sort or another, but you've wondered, "Hey, this video clip is choppy, the sound quality is poor, what the heck is going on?" This is where you have to take a look at the element known as bandwidth. Bandwidth is like a pipe that carries that data between computers on a network, whether it is an internal local area network (LAN) or the Internet itself. It is not a measure of the transmission speed of a network, but rather, the capacity the network to carry data to computers and other devices in a certain amount of time. The common units of measurement for bandwidth are the kilobit per second (kbps) and the megabit per second (mbps). Higher bandwidth networks are faster because they have more room for larger and faster data transmissions, like streaming media. There is only so much bandwidth available. There is higher bandwidth available the farther away from the end users you go. This means if you follow all the arteries and capillaries of the Internet back to the host servers, you will see faster transmission speeds. Users, at best, only enjoy a limited piece of bandwidth depending upon their Internet connection. Usually streaming media, particularly video, is limited to the data transmission rates of the network, hence the audio sometimes gets streamed at faster rates than the video. This may violate a law of physics, but it happens. Generally, in order to see all the bells and whistles that streaming media can offer, you need bandwidth that can support 10 mbps. When the technology people in your organization talk about your Ethernet connection, for example, they are referring to a network than can support data transmissions of up to 10 mbps. By comparison, the network supporting your basic dialup Internet account can transmit data to your computer at rates potentially between 28.8 and 56.6 kbps, which corresponds to the speed of your modem. Now, if you want something faster than a dial-up connection to the Internet, you are looking at "leased-line" connection. This means you have a dedicated phone line that does nothing but maintain a constant Internet connection. One type of leased-line is the Integrated Services Digital Network (ISDN). ISDN moves data over existing phone lines at speeds of up to 128 kbps, although you probably are really looking at data transmission speeds closer to 56 to 64 kbps. A second major type of leased-line is the T-1 connection, which in theory allows for data transmissions of 1 megabit per second. The other major leased-line type is the T-3 connection, which can accommodate data transmissions of roughly 44.7 mbps. But T-1 does not come cheap for dialup users. An increasingly popular option is the digital subscriber line (DSL). DSL is a method for transmitting data over a regular phone line. It is faster than your regular Internet connection, and can make use of the same copper wires that carry your basic phone service. In theory, it could support download speeds of 9 mbps and upload speeds of 640 kbps. There are basically two popular flavors of DSL. Asymmetrical DSL (ADSL) can allow users to receive content at transmission speeds of up to 1.5 mbps, and transmit at speeds of up to 128 kbps. Symmetrical DSL (SDSL) can allow users to receive and transmit data at transmission speeds of up to 384 kilobits per second. DSL's competition comes courtesy of cable modems. This is a setup that connects computers to a a box at the local cable company using a coaxial cable line. In theory, it would allow users to receive Internet content at some 27 mbps and to upload (send) content at approximately 2.5 mbps. The cable provider, however, serves as an intermediary to the Internet for the end user, and may itself only use a T-1 connection to the Internet, which means you get 1.5 mbps transmission speeds, roughly that of DSL. The advantage cable modems have over DSL is that they provide a continuous connection to the Internet without using a phone line. Now let's assume you are trying to access streaming media on a low-bandwidth network, like, say, an Internet dialup account at 14.4, 28.8, or 56.6 kbps. You might not see glorious full-motion, high-quality video and audio content that folks with faster Internet connections will. That's because you are actually receiving a slimmed-down version of streaming content. At a slower Internet connection speed, streaming media files need to be made smaller to fit through the lower bandwidth. This is done by a process called "encoding." Encoding removes some of the information that defines high-quality audio and video to make the streaming files more manageable to those folks viewing it at slower speeds. Now for the best part: all of the figures above assume that you are the only person attempting to view a particular set of streaming media clips. Think of what happens when 5,000 people with different Internet connections on different networks of varying speeds are attempting to access the same content from one host server! As more groups begin to use streaming media in their efforts, there is much larger set of issues, as Sara Robinson points out in an 8/23/99 New York Times article. Robinson points out that the servers that provide streaming media are contributing major congestion to the Internet. This is not only because they are streaming huge files. It is because streaming media needs to continually flow to user's machines. It does so in a way that effectively hogs a good portion of the bandwidth that other data uses. The more common forms of data transmitted over the Internet follows a protocol called TCP (transmission control protocol). TCP has a "control trigger" that basically makes computers slow down their data transmission rates by half whenever they hit network congestion. When the congestion is relieved, the machines are instructed to transmit at their normal speed. Streaming media, however, ignores these rules, in much the same way that a big car would run a red traffic signal. It tends to carve up more bandwidth for itself than other types of data transmission. Robinson notes that streaming media can peacefully coexist with other data transmissions, but that developers of streaming technologies have not yet really taken the initiative to solve the problem. In fact, if you wanted to physically increase bandwidth on the end-users' side to accommodate faster transmission rates than those of DSL and cable modems, we would need to replace some 300 million copper telephone lines with fiber optic lines. More people have been talking about the future potential of streaming media to deliver entertainment content. As more cable modems and DSL connections help increase the bandwidth available to end users, there is great concern about more people taking advantage of the increased volume of such content. Resources Cited RealNetworks Microsoft Windows Media Technologies VDO's LivePlayer Synchronized Multimedia Integration Language WebTechniques Magazine (September 1998) "Multimedia Transmissions Drive Net Toward Gridlock" Sara Robinson, New York Times (August 23, 1999) [free registration required] Resources Digital Media Association Broadcast.Net Discussion Lists on Webcasting World Wide Web Consortium SMIL Standard