By Dr. Philip Baczewski, Associate Director of Academic Computing
Back to the Basics: Bandwidth
Bandwidth: "The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second(BPS) or bytes per second." (www.webopedia.com)
Bandwidth has been in the news lately. You may have seen stories about "broadband Internet" services having difficulty catching on throughout the U.S. (http://www.washingtonpost.com/wp-dyn/articles/A45676-2002Jan14.html). The word "broadband" is used to describe Internet services which are faster than the normal dialup connection. So what exactly is "bandwidth" and why should you care? If you use the Internet, you may already know why you should care, but maybe a further explanation here is in order.
Bandwidth in History
In ancient times (around 1980), I first started using a modem (or acoustic coupler, as they were called in those days) to connect a terminal via a telephone line to a computer that was located in another building. The fact that you could do such a thing at all was remarkable. I'd dial the phone number, place the phone handset in the acoustic coupler (in ancient times, all phones had the same basic shape), and I'd be communicating with the remote computer at 300 bits per second. 300 bits per second allows about 30 characters to be transmitted every second. That's about 6 words per second or about 360 words per minute. While this rate was slower than my reading speed, it was still fast enough to work on computer programs, especially, since programming languages tend to use either short or abbreviated commands. You can imagine, my delight, however, when that 300 BPS modem was replaced with a 1200 BPS model.
Today, the Internet connection to my office operates at a transfer speed of 100 Megabits per second. That's 100 million bits per second -- I'll do the math -- that's 333,333 times faster than that 300 BPS modem. This means that I can now receive text faster than I can read it ( and often do). But more significantly, I can pull up a web page and see a full-color photograph without having to wait all afternoon for that photograph to be transmitted. This gets us closer to why bandwidth is important.
Bandwidth to a "T"
Let's explore for an example, the letter "T". To transmit the computer representation of the letter T requires one byte which is eight bits (as in "bits per second"). But let's suppose that we want to send a black and white picture of the letter "T" that takes up a 100 by 100 pixel space on a computer screen (if your screen resolution is 800X600 imagine a square which is one-eight the width of your screen). That picture would require 10,000 bits to represent. Let's say we wanted to use a extremely varied color pallet to decorate our T. We would need 32 bit planes to represent all possible colors. That increases the size of our T representation to 320,000 bits.
Suppose we wanted to animate our T for 5 seconds at 30 frames (or individual pictures) per second. We are now up to 48 million bits of information for our one little T. To get this T movie across campus from one computer to another would theoretically take only one half of a second (that's theoretical because there are other factors which effect the actual speed that data can be transmitted on a computer network). What if we wanted to retrieve that "T" movie over that 300 BPS modem from 20 years ago? It would only take 44 hours (almost 2 days).
The example above makes it clear that the Internet as we know it today would not exist at a bandwidth of 300 bits per second. Even though our black and white picture of the T could be transferred in 33 seconds, a page full of black and white graphics would take much longer. The color picture of the T would transfer in about 17 minutes. But notice that the greatest leap comes between that color picture and the animated version we imagined above. In actuality, digital video technology employs clever compression and other methodology for minimizing the amount of bandwidth needed, however, to move beyond static pictures and text still requires a great leap in available bandwidth.
Bandwidth and Today's Internet
On campus, we have quite a bit of bandwidth at our disposal and yet it still seems that the Internet is sometimes kind of slow. Although our campus network operates at 100 Megabits per second, which is quite handy for moving information around campus, our connection to the Internet operates at only 45 megabits per second. We have two such connections, but the aggregate bandwidth is 90 megabits per second, still slower than the on-campus network. But all over the Internet, many web sites may be connected at an even slower speed. The time that it takes your browser to contact a remote server and retrieve a web page is dependent upon the lowest bandwidth connection between you and that server and how much information is being transmitted across that connection (and remember that there are millions of users on the Internet transmitting millions of bits of information).
Most home Internet users still do so via a dialup modem. The fastest dialup modems are rated at 56 kilobits per second. For various reasons, it is unlikely that dialup modems will ever be much faster than 56 KBPS. This is 1700 times slower than our campus network. Still, at a theoretical 56 KBPS, it take only 14 minutes to transfer our imaginary "T" movie. This is a great improvement over 20 years ago, but still not very practical. But suppose you could have 384 KBPS available to you at home. That brings our movie down to under three minutes to transfer (assuming comparable bandwidth all the way to the source).
In actuality, the technical issues surrounding bandwidth and the operation of the Internet are much more complex, but our illustration above helps get a handle on why bandwidth matters where the Internet's development is concerned. To take the next leap, which is the integration of high-quality moving pictures and sound with Internet content, will require an across the board increase in available bandwidth, both within the core Internet network and to individual homes. To do so requires, requires a change in technology in home communications.
So how do I get my Bandwidth?
That change is coming, but it is coming slowly. It is coming so far as only two alternatives. Digital Subscriber Line (DSL) service from your local phone company can provide that 384 KBPS bandwidth or even greater, while replacing your old analog voice service. It allows you to talk on the phone and communicate with the Internet at the same time. Unfortunately, because of equipment limitations DSL is not available in all homes. Furthermore, it costs an average of $50 per month which is about twice what you'd pay for a typical analog phone line. The only hope of that cost coming down is competition, however, local phone companies are not known for inviting competition into their service areas (quite the opposite).
That leaves your local cable company as the only possible alternative for broadband service. My broadband cable service increased in price from about $50 per month to about $75 per month with no prior notification. My local cable company is notorious for bad customer service and they lived up to that reputation while I was trying to get my service disconnected. Luckily, I was eligible for DSL service and am marveling at the fact that I now consider Southwestern Bell to be one of the easiest companies to deal with. Still, if they decide to arbitrarily raise the price of the service, I have no third alternative to select.
The future of Bandwidth
Without that next quantum leap in bandwidth availability, the Internet remains a useful, but limited, information source. Just imagine digital video conferencing as easy to do as sending e-mail. Imagine posting movies of your kids on your personal web site instead of just still pictures. But don't stop there. Imagine a room in your house which can create a virtual environment and then create images of your family and friends within that environment so that you can have a virtual get-together with people conversing and coming and going as if the room were real. We're going to need a lot more bandwidth.