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Freequently
Asked Questions
Network
Basics
We
are truly in an information society. Now more than ever, moving
vast amounts of information quickly across great distances
is one of our most pressing needs. From small one-person entrepreneurial
efforts, to the largest of corporations, more and more professional
people are discovering that the only way to be successful
in the '90s and beyond is to realize that technology is advancing
at a break-neck pace---and they must somehow keep up. Likewise,
researchers from all corners of the earth are finding that
their work thrives in a networked environment. Immediate access
to the work of colleagues and a "virtual'' library of
millions of volumes and thousands of papers affords them the
ability to encorporate a body of knowledge heretofore unthinkable.
Work groups can now conduct interactive conferences with each
other, paying no heed to physical location---the possibilities
are endless.
You
have at your fingertips the ability to talk in "real-time''
with someone in Japan, send a 2,000-word short story to a
group of people who will critique it for the sheer pleasure
of doing so, see if a Macintosh sitting in a lab in Canada
is turned on, and find out if someone happens to be sitting
in front of their computer (logged on) in Australia, all inside
of thirty minutes. No airline (or tardis, for that matter)
could ever match that travel itinerary.
The
largest problem people face when first using a network is
grasping all that's available. Even seasoned users find themselves
surprised when they discover a new service or feature that
they'd never known even existed. Once acquainted with the
terminology and sufficiently comfortable with making occasional
mistakes, the learning process will drastically speed up.
Domains
Getting
where you want to go can often be one of the more difficult
aspects of using networks. The variety of ways that places
are named will probably leave a blank stare on your face at
first. Don't fret; there is a method to this apparent madness.
If
someone were to ask for a home address, they would probably
expect a street, apartment, city, state, and zip code. That's
all the information the post office needs to deliver mail
in a reasonably speedy fashion. Likewise, computer addresses
have a structure to them. The general form is:
a
person's email address on a computer: user@somewhere.domain
a computer's name: somewhere.domain
The user portion is usually the person's account name on the
system, though it doesn't have to be. somewhere.domain tells
you the name of a system or location, and what kind of organization
it is. The trailing domain is often one of the following:
com
: Usually a company or other commercial institution or organization,
like Convex Computers (convex.com).
edu
: An educational institution, e.g. New York University, named
nyu.edu.
gov
:A government site; for example, NASA is nasa.gov.
mil
:A military site, like the Air Force (af.mil).
net
:Gateways and other administrative hosts for a network (it
does not mean all of the hosts in a near.net.
org
:This is a domain reserved for private organizations, who
don't comfortably fit in the other classes of domains. One
example is the Electronic Frontier Foundation, named eff.org.
Each
country also has its own top-level domain. For example, the
us domain includes each of the fifty states. Other countries
represented with domains include:
au
:Australia
ca
:Canada
fr
:France
uk
:The United Kingdom. These also have sub-domains of things
like ac.uk for academic sites and co.uk for commercial ones.
The
proper terminology for a site's domain name (somewhere.domain
above) is its Fully Qualified Domain Name (FQDN). It is usually
selected to give a clear indication of the site's organization
or sponsoring agent. For example, the Massachusetts Institute
of Technology's FQDN is mit.edu; similarly, Apple Computer's
domain name is apple.com. While such obvious names are usually
the norm, there are the occasional exceptions that are ambiguous
enough to mislead---like vt.edu, which on first impulse one
might surmise is an educational institution of some sort in
Vermont; not so. It's actually the domain name for Virginia
Tech. In most cases it's relatively easy to glean the meaning
of a domain name---such confusion is far from the norm.
Internet
Numbers
actually
a 32-bit number, but is most commonly represented as four
numbers joined by periods (.), like 147.31.254.130. This is
sometimes also called a dotted quad; there are literally thousands
of different possible dotted quads. The ARPAnet (the mother
to today's Internet) originally only had the capacity to have
up to 256 systems on it because of the way each system was
addressed. In the early eighties, it became clear that things
would fast outgrow such a small limit; the 32-bit addressing
method was born, freeing thousands of host numbers.
Each
piece of an Internet address (like 192) is called an "octet,''
representing one of four sets of eight bits. The first two
or three pieces (e.g. 192.55.239) represent the network that
a system is on, called its subnet. For example, all of the
computers for Wesleyan University are in the subnet 129.133.
They can have numbers like 129.133.10.10, 129.133.230.19,
up to 65 thousand possible combinations (possible computers).
IP
addresses and domain names aren't assigned arbitrarily---that
would lead to unbelievable confusion. An application must
be filed with the Network Information Center (NIC), either
electronically (to hostmaster@nic.ddn.mil) or via regular
mail.
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Internet History
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Network
Basics
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General
Problems
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General
Questions
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Glossary
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Resolving
Names and Numbers
Ok,
computers can be referred to by either their FQDN or their
Internet address. How can one user be expected to remember
them all?
They
aren't. The Internet is designed so that one can use either
method. Since humans find it much more natural to deal with
words than numbers in most cases, the FQDN for each host is
mapped to its Internet number. Each domain is served by a
computer within that domain, which provides all of the necessary
information to go from a domain name to an IP address, and
vice-versa. For example, when someone refers to foosun.bar.com,
the resolver knows that it should ask the system foovax.bar.com
about systems in bar.com. It asks what Internet address foosun.bar.com
has; if the name foosun.bar.com really exists, foovax will
send back its number. All of this "magic'' happens behind
the scenes.
Rarely
will a user have to remember the Internet number of a site
(although often you'll catch yourself remembering an apparently
obscure number, simply because you've accessed the system
frequently). However, you will remember a substantial number
of FQDNs. It will eventually reach a point when you are able
to make a reasonably accurate guess at what domain name a
certain college, university, or company might have, given
just their name.
The
Networks
Internet
The Internet is a large ''network of networks.'' There is
no one network known as The Internet; rather, regional nets
like SuraNet, PrepNet, NearNet, et al., are all inter-connected
(nay, ''inter-networked'') together into one great living
thing, communicating at amazing speeds with the TCP/IP protocol.
All activity takes place in "real-time.''
UUCP
The UUCP network is a loose association of systems all communicating
with the UUCP protocol. (UUCP stands for 'Unix-to-Unix Copy
Program'.) It's based on two systems connecting to each other
at specified intervals, called polling, and executing any
work scheduled for either of them. Historically most UUCP
was done with Unix equipment, although the software's since
been implemented on other platforms (e.g. VMS). For example,
the system oregano polls the system basil once every two hours.
If there's any mail waiting for oregano, basil will send it
at that time; likewise, oregano will at that time send any
jobs waiting for basil.
BITNET
BITNET (the "Because It's Time Network'') is comprised
of systems connected by point-to-point links, all running
the NJE protocol. It's continued to grow, but has found itself
suffering at the hands of the falling costs of Internet connections.
Also, a number of mail gateways are in place to reach users
on other networks.
The
Physical Connection
The
actual connections between the various networks take a variety
of forms. The most prevalent for Internet links are 56k leased
lines (dedicated telephone lines carrying 56kilobit-per-second
connections) and T1 links (special phone lines with 1Mbps
connections). Also installed are T3 links, acting as backbones
between major locations to carry a massive 45Mbps load of
traffic.
These
links are paid for by each institution to a local carrier
(for example, Bell Atlantic owns PrepNet, the main provider
in Pennsylvania). Also available are SLIP connections, which
carry Internet traffic (packets) over high-speed modems.
UUCP
links are made with modems (for the most part), that run from
1200 baud all the way up to as high as 38.4Kbps. The connections
are of the store-and-forward variety. Also in use are Internet-based
UUCP links (as if things weren't already confusing enough!).
The systems do their UUCP traffic over TCP/IP connections,
which give the UUCP-based network some blindingly fast "hops,''
resulting in better connectivity for the network as a whole.
UUCP connections first became popular in the 1970's, and have
remained in wide-spread use ever since. Only with UUCP can
Joe Smith correspond with someone across the country or around
the world, for the price of a local telephone call.
BITNET
links mostly take the form of 9600bps modems connected from
site to site. Often places have three or more links going;
the majority, however, look to "upstream'' sites for
their sole link to the network.
@vskip
0pt plus 1filll @flushright "The Glory and the Nothing
of a Name'' Byron, Churchill's Grave @end flushright |
