21st Century Communication

From : thinrope.net/misc/report021

Introduction

Communication, data, speed, digital, security, Internet... All these words are all over the media, in most commercials and advertisements - there is no doubt that 21st century will be the century of information. And of course all the information should be accessible and here comes communication. So whether to call it Information Century or Communication Century is a bit unclear.

So what is this information all about? Why do we need it? Where can we get it? This and other questions arise...

What is information?
Information is everywhere around us. What most people consider it to be includes weather information, exchange rates, time tables, news, etc. But in a broad sense information is also a movie you rent nearby your home, the music CD you can buy in any music shop... Have you ever thought that your voice carried by the telephone company is also a kind of information? It is, believe me.

Digital vs. Analog
Until very recently, most of the information transmitted in the world was analog, i.e. some kind of continuous change of a certain property like color, sound, etc. And the main reason for that is that humans cannot perceive directly digital information, i.e. with strictly quantatized properties like colors can be either black or white (no gray), or something can be either on or off. Another reason was that there were no efficient means to store, transmit and convert between digital and analog form. With the advent of LSI and computing theory in general, the second reason is partially solved. But why, you will ask, we need digital at all? There is one BIG reason: any information in digital form looks the same and can be transmitted and stored without change and loss.

Lets think in terms of making multiple copies of one page of a book:

First, the analog way: You take the page and go to the best copy machine you can find. You make a copy of the page and send it to a colleague of yours. Assuming the mail is perfectly secure, the page will reach its first stop unaltered, but in the meantime it can be bent, rained upon, etc. Your colleague gets the page, goes to his (very good) copy machine, makes a copy and sends it to another colleague. After the page has been copied several hundred times it comes back to you and you discover that it resembles just barely the original: somebody has folded it and from that point all the copies have a black line in the middle, somebody's copy machine has spit some more toner, or even somebody spilled a cup of coffee over the poor page... Note that an alternative to mail/copier is a fax, but the quality will be worse!

So let's see how to do it digitally: First step is to digitize the page. For that you use a (good) scanner. If you are interested just in the contents (i.e. what is written, not how it looks) you can use your favorite OCR program to make a simple text file (we assume there is only text on the page). Whatever you decide, after that you have to send the file (which is now the digital copy of the original page) to your colleague. You can use either e-mail or just send a floppy (MO, CD, Zip...) by normal mail. When your colleague gets the file he sends it to somebody else to repeat the process. After several thousand people have read the file (and everybody printed it, some twice because of the spilled coffee on the first printout) you get it back and it is exactly the same!

Backbone and terminal connections
For a starter, let's look at how does your voice get from your home phone to your friend on another continent. There are three main segments of the information flow between you and him/her.

First segment is between your phone and your telephone company central. This is usually a twin copper-wire cable connection, but it may also be wireless in case of a mobile phone. You can safely assume that all the (speed) bandwidth of this connection is used only by you at the given time.

Second segment is between the central and your friend's telephone company central. This part consists of one or more inter-satellite connections as well as wire and fiber optic cables. This connection is not for the sole purpose of your conversation, but is used simultaneously for other phone calls, control data, faxes, Internet connections and who knows what else. This plays the role of a network backbone.

Finally, the third segment is between and your friend's telephone company central and his phone. This is more or less the same as the first segment and that is your friend's terminal connection.

Quality vs. Speed
Now let's consider what will happen if your neighbor decides to call at the same time as you do, to his friend who happens to be a neighbor of your friend from the previous example. Most likely both calls will be transmitted simultaneously by the (same) telephone company without a problem. We suppose that the company has more than one line for this particular route. Now imagine a lot of people (say several hundred) trying to do this at the same time. Does the long distance operator have to support this many lines? What if next day the same group of people calls some other group on another continent? Do we need a line between every two phones on Earth? Fortunately the answer is "No"!

A long time ago people have invented multiplexing, a way to transmit several signals over the same media at the same time. However this does not go without compromise in speed or quality. As well as it is not acceptable to have delay (i.e. low speed connection) in your telephone conversations, it is unacceptable to have errors (i.e. low quality connection) when transmitting your credit card number over the same telephone line!

How is speed measured?
Talking just about digital data, it is measured in bps - bits-per-second - where one bit is a value that is either 0 or 1. To say it in another way if you have to transmit raw information for example about who is (transmit 1) attending a particular meeting and who is not (transmit 0) and there is a list (in the same order) of all the names on both sides of the connection, you will need n bits for n people in the list. Another example is when you have to transmit text data. A long time ago a standard for encoding text data into binary (bit oriented) form was proposed, known as ASCII. For particular reasons one character is encoded with 8 bits and this 8 bits are called a "byte". So for one page A4 with 60 lines, 80 characters each you need 60x80x8=38,400 bits! And when it comes to photographic quality images or video (where every second 24 different images are needed) the numbers become really HUGE!

Current telephone system standards allow speeds up to 64 Kbps (1 Kbps = 1024 bps) which means roughly 2 pages of text per second - a good speed that made e-mail so popular way of personal communication. However...for real time video a speeds around 6-10 Mbps (1 Mbps = 1024 Kbps) are needed - very far even from the 128 Kbps that the relatively new ISDN phones can reach! And this is just the speed of the terminal connection to/from your home.

Now let's go back to the example of many people calling simultaneously. Let's assume they all have 10 Mbps connections. So what happens if 100 people try to use the full speed of their connections at the same time? Their (common) service provider will need 100x10=1,000 Mbps or around 1 Gpbs! Well, currently that is about the speed of the major backbones around the world. And there are several thousand million people using phone and Internet from their homes every day. Imagine everybody had 10 Mbps connection...

The future
What future will bring us nobody knows. Looking at the latest trends in communication, however, I think that the huge demand for high speed low cost communication will be strong enough solutions to be soon found.

Soon everybody (me) will have fast enough connection from his home and office and I won't need a coffee break to upload the file that you've just read...