There are corporations an government agen-cies all across the country that have computers you will want to get your hands into. But you're not going to want to get your hands into your wallet to pay for all those long distance calls. The solution? Public Data Networks (PDNs).
A PDN is a network of hundreds of computers scattered nationwide. You call up one local to you, then type the address of the computer system you want to connect with. The "address" is usually something like a phone number. When you enter a valid address, the login display for the desired sys-tem will appear. You are then
able to interact with the system as if you were directly connected to it, when in reality everything you type is being bro-ken down into chunks of text (packets), possibly compressed and encoded, then shipped across the country, from one computer to the next, until it reaches its destination.
There may be hundreds of other sessions going on simultaneously from points throughout the net-work, as thousands of users interact with the many computers on the net. Sending messages this way is known as packet switching. The intermediate computers that do all the work are called PADs, or Packet
Assembler/Disassemblers, because they take incoming packets of data, strip away the en-coded insulation which tells that PAD where the packet is headed, then reassemble the data with new directional
information, sending it further along the route.
Hackers take great glee in connecting with a PDN. Once there, a hacker can try out various ad-dresses at random. In a matter of minutes, he will find himself with a wide variety of login prompts to crack, all made through a local phone call. The most well-known PDNs are Telenet and Tymnet, and there are also
international packet networks, and networks in other countries as well. Generally you can call any one of these services to get a list of PADs in your area you can dial in to.
Other Networks
The only other network that counts is the Internet.
Internet is an international network of net-works. There are academic networks, government networks, businesses and organizations throughout the world, all connected together (by PDNs) to ex-change ideas, software, technologies, gossip and guacarnole recipes.
Before Internet there was ARPANET, a military network which has since been replaced by MILNET (a well-guarded network of United States military sites) and other smaller networks used by the US military. Altogether, these make up DDN, the De-fense Data Network. DDN is now just one of many networks participating in the Internet.
Others include the National Science Foundation NETwork (NSFNET), which includes supercom-puter centers and other research sites funded by the NSF. CSNET is a network established to encourage cooperation between sites doing development work in computer science. JANET is the United Kingdom network, one of many national networks around the world that is bridged with the Internet. Internet is
truly a global community.
Some of the pay-for-play services offer access to the Internet. Many university computer accounts are connected to it. Basically, having an "in" with the Internet allows one to travel around the world and back without leaving your armchair. We were talking before about packet switched network addresses. An Internet address is a series of code words punctuated with periods, and refers to one particular computer in the millions that make up the Internet. A typical Internet address might be "danielk@cs.zowie4.uboulder.edu." We can deduce that at the University of Boulder there is a computer in the computer science department
called zowie4, and on that computer there is a per-son whose first name is Daniel, and last name be-gins with K. The "edu" is a standard thing stuck at the end of educational computer addresses. Other identifying components used are:
COM for commercial sites,
MIL for military sites,
GOV referring to governmental organizations,
ORG for non-profit organizations, and
NET meaning Internet administrator sites.
An Internet address may also end in a two-character country abbreviation. Some exam-ples of these are:
AUAUstralia
IL Israel,
US United States
JP Japan
UK United Kingdom
DE Germany (tricky! DE is for DEutschland).
