VoIP and Bandwidth

VoIP is dependent on a certain amount of bandwidth and it is only due to the widespread acceptance of broadband modems that (useable) VoIP is potential. So - what exactly is bandwidth and how else does it affect VoIP? Bandwidth refers to the total of digital information that may be transmitted in a certain time period. Internet connections are usually measured in KiloBits Per Second (kbps). Your connection can be rated at 128/512 kbps. This means that the upload stream (leaving your computer) has a utmost bandwidth of 128 kbps and download stream (coming to the computer) has a utmost bandwidth of 512 kbps. To give you an idea of what that means in real-world terms consider the size of a web page which is made up of a couple paragraphs of text and a few illustrations. The size of this web page will be around 3,000 bytes or 24,000 bits. At a download speed of 512 kbps this page can be viewed in 0.05 seconds - almost instantaneously. Wait a minute (you may be saying) - web pages don't load that fast on my computer. You won't email your utmost transfer speeds for a few of reasons. Most important there is latency - the delay induced by the physical limitations of every piece of hardware the data is passed through. Latency is introduced through the transmission medium, a routers that determine the path the data may require, and storage when the data eventually reaches your computer. More delays are driven by pathway congestion, error checking, transmission negotiations and extra data which is sent with the web page to determine the type of data being sent and its origin and destination. What this means for VoIP is that enough bandwidth must be supplied to allow for the transmission of the actual voice data in real time as well as more bandwidth for the overhead required for any data transmission. The actual amount of voice data depends on the codec (enCOder/DECoder) utilized to compress the data, and this can range anywhere from 16 - 64 kbps. More overhead totals about 10 - 24 kbps for a total load of about 26 - 88 kbps. Once it comes to VoIP it is wise to err on the side of caution - it is better to consider that you will require 88 kbps. That translates into an Internet connection that can cover at least 128 kbps on the upload side. More bandwidth might allow others in the household to surf the net or download files while you are talking on the phone. In case you wish to apply conference calls potentially more bandwidth may be needed. There is there are no easy rule for determining the amount of bandwidth that a particular household will need. Count on 128 kbps as a minimum but consider going up to the maximum available if you have many computers and additional gear attached to the Internet. Note that these rate are for uploads - the download speeds are normally quite a bit faster and present no condition for VoIP.