There are many types of files available for download from the Internet. Some are simple text files and others
are programs such as word-processors or games. Most of these files have to be completely downloaded to your PC
before you can use them. Why can't you view a partial text file? Well, theoretically you can, but by the nature of
Internet downloads a partially downloaded text file is likely to be scrambled and unreadable.
All downloads work by dividing the original file into small packets which are encoded with their destination and
their order in the data stream. This last bit is important as packets can arrive in any sequence, but thanks to
their unique ID, they can be reassembled in the correct order.
The Internet is a vast array of pathways that carry millions of bits of data every second. In order for that
data to reach its destination as quickly as possible, every pathway is open to every data packet. One packet may go
via Bombay, another via Tokyo, but they all end up at their correct destination.
Video streaming follows the same basic principle of breaking data into packets. Instead of waiting for all the
data to arrive, however, a streaming video can be watched as it is downloading. This allows the end user to see the
video almost immediately after clicking the view button, whereas if the entire video file had to be downloaded
there could be a delay of several minutes or even hours.
Video streaming is possible thanks to a set of streaming protocols. Unlike protocols designed for other types of
digital data, streaming protocols prioritize data packets so that they arrive in the order they are sent. Streaming
protocols can also allow for lost data packets so that the streaming video continues to play even if a few packets
One of these streaming protocols is known as Real Time Streaming Protocol or RTSP which allows the viewer to
remotely control the data stream so that the streaming video can be paused, rewound or fast forwarded. Actual
delivery of the video stream is handled by the Real Time Transport Protocol or RTTP and the Real Time Control
Protocol or RTCP.
Video Broadcasts - Webcasts
Video broadcasts on the Internet are sometimes called webcasts, and use the same basic principles of video
streaming. Unlike most video streams, however, streaming video
webcasting is live and can only be viewed at one particular time, just like a TV broadcast.
Webcasts usually require more resources than simple video streaming because of the potentially large number of
viewers that can be watching at the same time. Each viewer requires a certain bandwidth (the rate of data
transmission), so once the amount of bandwidth reaches the maximum capacity of the server, no more viewers can
watch the webcast.
One way around this is to use a protocol called multicast in which one data stream can be viewed simultaneously
by many people. Multicasts are often blocked by firewalls, however, limiting their usefulness to private
Internet video conferencing is sometimes called web based video
conferencing. This involves setting up a two way or multi way communication channel so that each participant
can see and talk to the other participants.
Web conferencing is based on the same technology as webcasts, since by their nature they must be 'live' but
because each party needs to interact with the others it can be even more technologically demanding than