Bandwidth restrictions

So lets look at the bandwidth issues that we are facing when we try to stream media.
 
Basically, a lack of bandwidth is the one thing that affects the quality of audio and video that we can deliver to the viewer. The smaller the amount of data we can push down a connection to the internet at any time the worse the quality of the audio and video we can deliver. And another problem that we have is that most connections are not even stable We get network congestion and we can get poor connections and, if that happens, it degrades the quality of the audio and video even further.
 
So one of the things that we need to be looking at is the ability to perform a step-down version of our streaming media to allow it to be experienced at different bandwidths as the network performance changes. And the method for doing that is multiple bit rate or short stream if you are using Real Networks. This lets you put different variants of your video and audio in a single package stream so that, as the network bandwidth changes, a different version can be sent down to the user.
 
Bandwidth effectively tells us how much room we have got on our connection to the internet for sending data down. In other words how many bits we can send down a connection to the internet every second. Infact that is how we measure it - in bits per second. However, computers are very fast and we can send lots and lots of bits per second. So we have a couple of specific measurements. Kilobits or Kbps which is 1000 bps, and Megabits or Mbps which is used for higher speed lines. For example a fixed line from a company’s main network into internet might be 2 Mbps or even 10 Mbps.
 
In computer terms data is normally referred to in terms of “Bytes” rather than “bits”, where 1 Byte is a group of 8 bits. A Kilobyte or KB is in this case 1024 bits and a Megabyte or MB is 1024 x 1024 bits. (notice the difference in the case of KB for 1024 bits and Kb for 1000 bits).
 
So lets now have a look at the kind of bandwidths that are available over different connections to the internet and why it is not quite as high as we expected it to be.
 
For instance a typical 56K modem is, in theory, capable of transmitting or receiving 56000 bps.
 
However a good number of those bits are used up for administrative purposes, such as checking that what you have sent is correct, or getting the correct address on it so that it goes to the right place. As a result, in reality a 56K modem is only capable of of transferring 5 KBps or 40 Kbps.
 
So, typical figures for different connections will probably be:

• 28.8K Modems will transfer only 2.5 KBps or 20 Kbps
• 56.0K Modems will transfer only 5.0 KBps or 40 Kbps
• Dual ISDN will transfer only 11.5 KBps or 92 Kbps
• TI / DSL will transfer only 43.75 KBps or 350 Kbps

• 160 x 120 pixels @ 8 – 10 fps (acceptable quality of picture and reasonably acceptable experience)
• Higher bandwidth 100K connection 320 x 240 pixels @ 12.5 fps (twice size so 4 times data, at half video rate)
• Broadband 300K connection 320 x 240 @ 25 fps (full video rate)