| Computing and the Internet |
This document is the outline of a short workshop given at Northwestern
University on 3/14/97 at the AT Techfest The workshop gave an introduction to
networks, networking, the distinction between local area networks (LANs) and
wide area networks (WANs), and the Internet. An overview of network protocols
and services was given A brief history of the microprocessor in honor of its
25th anniversary and a discussion of trends in computing concluded the
workshop. All links used in the workshop can be found in this document. Some of
the discussions are included as well.
Warren A. Kibbe, Ph.D., © 1997 Northwestern University
What I would like everyone to leave this talk with is a better understanding of
what makes a network, how information is sent on a network, and how common
Internet protocols like the web operate, and how the Internet can be useful to
you in your research and your teaching. First off, this presentation is given
via the web, and one of the major advantages that giving a presentation over
the web offers is that the talk is accessible afterward. That is, you can go
back to the web, and find the presentation and follow along with it at your own
pace, and even expand upon points that you don't have time for in the formal
presentation. As I am sure you are all aware, the world wide web, or simply
`the Web' has become an incredibly pervasive part of the American culture in
the past two years. Part of that is because of the flexibility of the web, the
fact that the web is platform independent (it does not depend on a particular
operating system or software), and its ability to convey information
graphically. With most browsers, you can either "Open" a location, meaning you
type in the uniform resource locator, or URL, or click on a "link" that
contains the URL already. During this talk I will rely on existing links, since
it is much quicker than typing them in.
For instance, the Medical School's Integrated Graduate Program brochure is on
the web:
IGP
Bulletin
Northwestern also makes a great deal of information about its own networks
available on the web:
NUNet
Maps
I make some additional information available that is specific to the Medical
School:
NUMS Subnets
Finally, there are lots of fun services that are freely available on the web:
Greeting
Card
So, how does all this work? At the most basic level, for information to travel
between two computers there must be either a dedicated connection between the
computers, or a "virtual" connection. A dedicated connection would be a single
cable connecting two devices, where each computer would be sure that anything
it sent on that cable would be received by the other computer. This isn't very
flexible, and if you tried to hook up more than just a few computers to each
other with dedicated connections, you would quickly end up with a enormous
number of cables and ports on each computer. What makes more sense is to send
out each bit of information with an address imbedded in it, serving to open a
virtual connection between two computers rather than a physically exclusive
connection. With the Internet, the address of each device on the Internet is
known as an IP number, or Internet Protocol number.
The current IP system uses
4 bytes to describe the address of the sending computer (or device, since
printers and other pieces of hardware can send a receive information on a
network) and 4 bytes for the address of the receiving device. IP numbers are
normally written in decimal as xxx.xxx.xxx.xxx where each set of three xes are
a number from 0 to 255 (2 to the 8th power, since one byte is 8 bits, a a bit
can either have a value of 0 or 1). In the early days of the Internet, when it
was developed by funding from the government agency ARPA (and called arpanet,
which later became bitnet, and finally evolved into the Internet), 4 bytes, or
2 to the 32nd power (4,294,967,296 addresses) was thought to be more than
enough for any conceivable network.
Now there are plans underway to upgrade the
IP4 system to IP6 (6 bytes or 2 to the 48th power), and include a security
layer at the packet level. I don't really want to discuss security and the
Internet, but one downside of the Internet, particularly for businesses, is
that any computer on a physical
subnet or LAN will see all the traffic destined for any device on that subnet.
That means that someone could easily write a program to "sniff" the packets on
a subnet, and get information being sent on it.
To get back to the main point, on the Internet, information is directed by IP
address. A single message sent between two devices on the Internet is sent
inside a packet. A packet contains the IP address and routing
information in a header . Next comes a description of the information
included in the packet, and finally the actual information in the packet.
Without muddying the waters too much, packets are sent to ports on a
computer. This port concept allows a single computer to run multiple network
services simultaneously. For instance, some common services (also called
protocols, just to confuse you) are Telnet, FTP, gopher, and of course the
world wide web. By common convention, Telnet uses port 23, FTP port 21, gopher
port 70, PH uses 105, and the web (http) uses port 80.
Cisco has a very complete description of IP addresses and subnets at
http://www.cisco.com/univercd/data/doc/cintrnet/idg3/idgvlsm.htm.
For those of you who have used the web, ftp or telnet, or any other service on the web,
you have realized that when I give an example of a URL, it uses a "human readable" form,
rather than four digits. For instance, the ip number for the computer where this document resides is
165.124.225.182, but when I write the URL for the server, I write
www.basic.nwu.edu. The reason I can use the name and
the number interchangably is something called the Domain Name Service, or DNS. There
is a big look-up table for all the computers on the Internet that maps IP numbers to DNS entries,
and vice versa. At NU, many services,
such as the Windows FTP server nuns.acns.nwu.edu and
many library services require that computers
logging into these services have valid DNS entries and come from the nwu.edu domain for
security and also licensing reasons.
The main difference between WANs and LANs is the number of computers connected
to a LAN and a WAN, and bandwidth of the connection. For instance, our campus
backbone, NUNet, is a WAN with multiple high bandwidth segments. Most LANs are
a single subnet, and connect a department, or a floor of a single building. At
NU, our subnets and NUNet allow the transmission of TCP/IP packets (the full
name for Internet packets), AppleTalk (Macintosh) packets, IPX (Netware)
packets, and NetBIOS (Windows) packets. If your computer supports one of those
protocols, then you can "talk" to other computers using those protocols
anywhere on NUNet. With TCP/IP, you can talk to computers anywhere in the
world, since we have a connection between NUNet and the Internet.
Map of NUNet WAN
I know I have run through a lot of material in a very short period of time. To
recap, the Internet standard for sending information between two computers is
TCP/IP. Two devices (like two computers, or a computer and a printer) can send information
to each other in TCP/IP packets if they have known and unique IP addresses.
Built into TCP/IP is the concept of virtual ports, where each port can
have different services bound to it. For instance, the web is generally bound
to port 80, so all http: requests that are sent out go to port 80 by
default.
We've talked about networking issues so far. Why should you care? One reason for
investing in computers and computer infrastructure is for the access, management and manipulation
of information. As I am sure that everyone today is aware, there is an increasing amount of published
material in practically every discipline. How much information is available?
According to a study by Ernst and Young, the volume of
published material doubled from 1880 to 1930, again from 1930 to 1960, doubled
from 1960 to 1970, and is currently doubling every 18 months. Keeping track of
the mass of publication, let along accessing and analyzing
information in this sea of data is difficult at best. To help manage this
overwhelming mass of data, computing solutions using search engines and
"intelligent agents" have emerged to let us skim and peruse huge
databases of data, looking for the few kernels of relevant information from the
warehouses full of data fodder. The promise of these new technologies is great -
they should allow us to have access to just the information we are looking for,
without having to wade through enormous amounts of similar or related material
for the fact that we are seeking. Along with this promise is a danger - we do not
want to filter out related or tangential information that may give a key insight
into a problem.
One of the benefits of life after World War II in the United States is that we have
experienced 50 years of uninterrupted posterity and growth. As a part of that growth,
we have much better access to information, and as the cost of publication plummets,
our information output skyrockets. For instance, the amount of information available
in printed and electronic form is shown in the graph below.
The only technology that we currently have that has the promise of dealing with this
explosion of information in the near future is digital computing. Fortunately, along
with the exponential growth of information, we are experiencing an exponential growth of digital
storage and computational power. The cost of storage and computer memory is plotted below:
New storage technologies, such as DVD, should continue to push the cost of storage down, with
storage costs less than a penny per megabyte by the turn of the century.
Similarly, the cost of computation, or computational power, has dramatically declined. The computing
ability of a commodity desktop computer today approaches that of a midrange ($50K-100K) workstation
of just a few years ago. Likewise, the graphical display capabilities of today's Macintosh and
Windows computers rivals that of a high-end Evans and Sutherland graphics workstation a decade ago.
All of this computational and imaging horsepower on your desk for about $3,000!
Since the first microprocessor was fabricated by Intel in 1971, we have seen a
tremendous revolution in the way that computers are used for research,
education, and business. In 1971, the mainframe was the way you acquired
computing power. They were expensive, large, and required a lot of maintanence.
Today, for less than $3000 you can have a computer on your desktop that has
more computational power than a 1972 IBM 370, and has a crisp 17" color
monitor. Processing power is generally not the bottleneck for desktop computers
today - I/O throughput and storage is more of the issue, especially for
modelling and imaging applications.
CPU advances, both in manufacturing practices and archetecture, are driving much of the increase
in performance seen in this graph. According to
"Moore's Law" the complexity and performance of
integrated circuits will progress at an exponential rate, roughly doubling every 18 months. This
observation was made in 1966 by Gordon Moore while at Fairchild Semiconductor, based on
10 years of watching the semiconductor
industry. In 1968, Moore, Bob Noyce and Andy Grove left Fairchild Semiconductor
(where Noyce had invented the integrated circuit in 1959) and formed Intel. Grove is currently
the CEO of Intel, and 30 years later Moore's predictions have been borne out
by 25 years of growth in the microprocessor industry. As you can see from the following graph,
processing power continues to increase, and the cost of computing continues to decline.
Links to a few cpu manufacturers
Searching the Internet
Searching & Info servers
- NU: Searching the Internet
- Alta Vista: Main Page
- Infoseek Home Page
- Internet Search
- Lycos Search Form
- WebCrawler Searching
- Yahoo
Resources for the Life Sciences
I hope that this presentation helps you better understand the nature of the Internet, and at least
introduce you to a few of the advantages that the Internet offers. For a compilation of my favorite
hundred or so sites, see:
http://www.basic.nwu.edu/bookmarks.html
Disclaimer:
This article does not constitute an official Northwestern University policy or represent
university views. No guarantee, warranty or claim is made or should be implied by the
content or absence of content.
Any services, facilities, or other sites listed in these pages are strictly listed as a
convenience to the reader. No endorsement of the content of listed sites
or identity of any published organization is implied or intended.
last modified 3/13/97
Please contact Warren Kibbe if you have
comments on the content of this page or others at www.basic.nwu.edu.
The END