Networks: A superficial overview

I'm sitting at home nursing a cold. But I thought I'd jot down a few thoughts while bored to death. I wasn't sure if we'd get together before your deadline and so, the thoughts I jot will be related to networks in general. I hope this isn't too patronizing. I suspect you know much of this already, but I don't know what kind of audience you intend to reach, nor what you want to tell them about the technology itself. The stuff below isn't exactly accurate. But it's good enough to get the idea across. I hope you can extract something useful from it.

The technology of networks is simply the continuation of the evolution of communications. It is most easily understood by comparing it to the more primitive species.

Early cultures communicated over long distances with drums and smoke signals. In both cases, there was a code that consisted of either the presence or absence of the signal. Smoke, no smoke, smoke, smoke, no smoke. (I imagine it was more complex than that, but the basic idea is there.) Jumping forward in time, we get to the electronic age. An electrical circuit can be made to move a hammer attatched to a magnet. The person at one end hits a hammer on a spring and closes the circuit. The hammer, spring and magnet at the other end responds in kind. The presence or absence of smoke has become the dot and dash of Morse code. But's still done manually.

A.G. Bell gets into the act, and finds a way to make the vibration of air open and close that same circuit. Because the voice is vibrating much faster than the hand hitting the hammers, the hammers are going so fast, they don't sound like dots and dashes any more. They sound like a human voice.

Now, imagine a box with a typewriter keyboard that sends a very rapid dot-dash pattern for every key pressed. If you listen to it on a phone line it's so fast it just sounds like a peculiar high-pitched whistling. Early machines used an extention of the Morse code, invented by a guy named Baudot. Each character typed is translated into a combination of 5 dashes and/or dots. The TTY (later called the TDD) was born.

However, the information contained in 5-bit patterns (each dot or dash being a bit), isn't sufficient to represent upper case and lower case and punctuation and numbers and foreign characters and ... and ... and. Baudot is only capable of representing 32 characters. Most computers today use an 8-bit code called ASCII (the American Standard Code for Information Interchange), which is capable of representing 256 unique characters.

Modem = Modulator/Demodulator. It is a device which converts sound into bit patterns and vice versa. (Without getting too deep into it, it extracts information from a signal that is something like the way a radio extracts information from it's signal. There is a "carrier signal" that indicates a connection between the two machines, and in synch with that is another signal that contains the actual information. Modems separate the carrier from the information.)

OK, so now we have computers sending 8-bit smoke signals over telephone wires, and modems which can convert those smoke signals to printed text. (Graphics and sound too, these days, but that's more than I want to get into.)

Those same whistling signals can be saved on magnetic tape cassettes exactly the same way answering machines can save a voice message. And there's no rule that says the magnetic tape has to be a long thin strip. It can be a big flat, circular piece of plastic, painted with a magnetic paint... a floppy disk.

Suppose someone paid for the phone line between two computers to be dedicated and constantly in communications. Or perhaps they buy time on a satallite link. (Satallites only convert the same sounds or bit patterns to radio waves and back again.) Just multiply that concept by about half a million. Voila: The Internet (and networks in general).

**CHECK THIS CAREFULLY - My history is a bit sketchy. Get a second opinion.**

Several years ago (late 60's?) a branch of the Department of Defense known as ARPA (the Advanced Research Projects Agency), funded a project to establish a permanent connection between a few computers. This proved to be VERY practical, and everyone got on the bandwagon. ARPAnet consisted mostly of universites doing military research, and commercial agencies that did business with the Pentegon.

Meanwhile, a few computer geeks with lots of time but no money tried to do the same thing. They called their network Usenet. Usenet members couldn't afford a leased phone line. So instead, they set up a system whereby every day, at regular intervals, each computer would automatically dial up another computer, send a bunch of info across the line, and then hangup. The next computer in the chain (or relay) would store the messages, articles, and programs that it had been sent, until it was time for it to forward them. Not surprisingly, this is known as store-and-forward mailing. The Usenet crowd decided that this system could be used to create catagories of information. This evolved into the Usenet newsgroups.

The last important player in the game was the National Science Foundation (I *THINK*) who got colleges without military funding onto a new network Because It's Time -- BITnet. BITnet's been kicking around since ... '83? '84? Somewhere around there.

There was a movie several years ago called "War Games". It's all about how this kid breaks into a military computer network and nearly starts World War III. A week after the movie came out, the Pentagon issued a statement saying that their system had never been breached, and that this speculative work of fiction, while entertaining, had no basis in truth. Then, they split ARPAnet into two groups: MILnet: exclusively for the military and Internet: everybody else. What a coincidence. ;-) (P.S. My cronies in high school and I were breaking into the ARPAnet long before this movie came out. So once again, the military is full of horseshit.)

With each passing day, the distinctions between Usenet, BITnet and Internet grow more and more vague, as more info gets transfered between them. Many sites belong to more than one network. These are called "gateway" sites, because they act as a gate for other computers. For example, Gally's not on Usenet, yet we get the Usenet newsgroups, and can send mail to usenet sites. That's because our mailer recognizes the IN% as meaning "send off campus" and each node in the relay knows that an address ending in .uu.net is bound for Usenet. Eventually, somewhere down the chain, that message reaches a computer that is both on BITNET and Usenet. The message leaves BITNET and enters Usenet.

About the only thing I didn't touch on above is transfer protocol. Suffice it to say that messages are often broken up into managable sizes in order to reduce the load on the system. Each portion of information (i.e. packet) has to have information added into it that tells where it's from, where it's going to, and how it fits into any packets sent before or after it. This information is then stripped off at the destination, and the packets are reassembled into a complete entity. The adding and stripping of "mailing labels, stamps, foam packing, and industrial strength tape" is collectively known as transfer protocol. That's how the VAX decides that some incoming packet is (a) a file to be RECEIVED, (b) a mail message, (c) an interactive RELAY message, (d) a NEWS article, or (e) none of the above.

The future: I don't really have a clue as to *HOW* cable television works. However, as the world moves at an ever-increasing rate towards multimedia, the television, telephone, and computer will merge into a "media unit". Interactive television is already here in DC, in a very primative way. (If you have cable, look for a station displaying a menu. Somewhere in the high 20's) VCR's are nothing more than fancy tapes or diskettes. Pictures sent electrically across a wire still have to be encoded and decoded. It's just not as simple as ASCII any more. The phone system is changing to fiber optic cable which sends those dots and dashes as pulses of light, rather than electricity. With fiber optics, more information can be sent simultaneously on several different threads of the cable coming into your home. This means that complex information such as a moving picture, does not have to be sent one bit at a time. This is what will make the videophone a practical reality. (Right now, the best I've seen is still a bit choppy. A nice gimmick but not ready for prime time yet.) Supposedly, all this stuff is going to hit the consumer market sometime in mid-1994...

For futher reading: Pay attention to anything in the news about ISDN -- the new technology for hooking phones to high-speed computer networks. And see if you can get your hands on an issue of "Wired" magazine.

Good luck assembling this jumble into a coherent whole. I just jotted things down off the top of my head. That history isn't exactly accurate. See if you can corner Kevin Casey or Bob Herbold. Both would probably be able to give you a better history of the players.

Date sent: 27-SEP-1993 13:16:37

I'm an Applications Programmer for the Center for Assessment and Demographic Studies.

As for clarifying the difference between the "VAX" and the various nets... That's a tough one, because I'm not sure I understand the question.

The nets are a collection of computers tied together by phone lines (and satallite links). Think of a spider's web. The VAX is merely one of the computers in that collection. There isn't a dichotomy between the VAX and the net. We're part of of it. The VAX is no different from a PC, except that it's bigger, faster and has more communications ports (modems, or direct lines).

As I mentioned in the end of my last message, the future is just around the corner. For example, I have a special board in my PC called an Ethernet board, which is like a very fancy internal modem. Without a regular phone line, I can sit at my desk and at the C:\> prompt, I can TELNET and FTP and send mail without involving the VAX at all. My PC is a node on the Internet. The point I'm making here is that the only significant difference (in terms of hardware) between the VAX and the PC is that the VAX can support more people simultaneously. At the moment, those Ethernet boards are still pretty rare on campus, and they do require some special setup by Computer Services, as well as a connection directly to the fiber optic cable. So you can't go out and buy one for your home PC... yet. However, the ISDN (International Standard for Digital Networking???? I'm guessing) standard is supposed to change all that within two years.

Did that help clarify things?