cs 100 june 12, 2007
The Internet.
The Interstate highway system uses roads to link states together.
The Internet, in a similar fashion, links networks to each other.
A LAN (local area network) traditionally has a maximum diameter of 6
miles/10 kilometers, but is usually much smaller. UTK's
network is a LAN. A MAN (metropolitan area network) can extend to
about 30 miles/50 km. There used to be a MAN that
connected UTK and Pellisippi State together--the two campuses are about
15 miles apart. A WAN (wide area network) can
extend to any distance around the world, but current WAN protocols
could not be used for future communication between, say,
planets. The Internet is the prototypical WAN--but there are
other WANs. There are actually two internets in the U.S.--
internet1, which includes commercial, government, etc sites, and
internet2, which links many academic sites. UTK has two
main internet gateways--a gateway to I2 in Stokeley Management Center,
which handles most of the traffic from the labs,
academic offices, etc, and a gateway to I1, which handles most of the
Residence Hall traffic. I1 and I2 connect together in places.
which is why you can get to www.newkids.com (or whatever) from crux7 in
our labs, and you can get to the cs100 site from your
home. Internal links in UTK's LAN let you connect to the
cs100 site from a dorm room without having to exit the LAN to the
internet.
Every host on the internet gets a unique indentfying address (but we'll
see how this statement needs qualification!). IPv4
(internet protocol version 4--the most common protocol) uses 32-bit
(4-byte) addresses. IPv6 (which is slowly replacing IPv4)
uses 128-bit (16-byte) addresses. These addresses are usually
presented in the format: 160.36.59.6 where each of the 4
numbers
is 1 byte/8 bits long, and is between 0 and 255. All
internet addresses that start with 160.36 are part of UTK. Other
sites,
commercial, academic, etc, are managed in a similar fashion, although
some sites are identified just by the first number
(e.g. addresses that start with 18. belong to MIT) and some are
identified by the first three numbers (e.g. www.newkids.com
is at a site that starts with 204.13.160). To see any address on
the internet: go to the start
menu on your PC, select run,
type
cmd (for command). This
brings up a window with a unix-like ">" prompt. the command nslookup and an alias will give
you the IP address for that site--e.g. >nslookup
crux3.cs.utk.edu will come back with 160.36.56.122, which
is the IP address
for crux3.
Some caveats to the above. The IP address of your PC at
home may change: for example, if you connect to the internet with
a dial-up modem, your ISP (internet service provider) has a pool of
valid IP addresses and will assign one to you. If you hang
up and reconnect, you'll probably be assigned a different IP
address. Next, what is very common is to have a high-speed
connection at home through Comcast, BellSouth, etc. Typically the
connection comes in through a router, cable modem, etc.
The router/cable modem/etc does indeed have an IP address on the ISP
side, but it typically translates this IP address into
a "virtual" address on the PC side. For example, the ISP side may
have the IP address 69.144.22.110 (which will be unique
across the entire worldwide internet). But on the PC side you
might have the "IP" (in quotes here, since it is not a true IP
address, but rather a virtual IP address) address 10.10.3.1. If
you have several PCs hanging off the router, they might have
"IP" addresses 10.10.3.1, 10.10.3.2, and 10.10.3.3. You are
paying for just the one real IP address, and the 3 PCs share the
bandwidth. (Try a nslookup on 10.10.3.1). At hundreds
of thousands of other locations around the country, PCs sitting
behind a router may also have "IP" address 10.10.3.1. To
see what IP address your PC has, or thinks it has: start, run, cmd
as previously described, then type the command ipconfig to show your
PCs IP (or "IP") address, the subnet mask (don't worry
about this), and the gateway--which is the next stop on the path to the
internet. The use of virtual addresses has helped prevent
the internet from running out of possible IP addresses.
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A bit about LAN, MAN, and WAN technology. The technologies
used here differ from one another. The prototypical LAN
medium is Ethernet, although there are a wide variety of other LAN
protocols. Ethernet equipment ranges from very cheap
to quite expensive. UTKs Network Services can put an Ethernet
card in your PC for about $10 so that you can hook your PC
up to the Ethernet outlet in your dorm room. You'll get a 5
megabit connection--5 million bits per second--here. This sure
beats a 56K dial-up phone modem. Ethernet comes in various
speeds--from 5 megabits to 100 megabits up to gigabit
(billions of bits a second) Ethernet. Don't ask Network Services
for a gigabit Ethernet card for your PC for your dorm room.
You would pay a whole lot more than about $10, and the Ethernet outlet
is only running at 5 megabits anyhow. But some of
the main network connections around the UTK campus are running in the
multi-gigabit range.
Ethernet, for technical protocol reasons, is quite limited in
range--generally, the faster the Ethernet, the shorter the range--
so you will not see any gigabit Ethernet segments extending 6
miles. Other network protocols include FDDI (fiber distributed
data interconnect), ATM (asynchronous transfer method--suitable for
voice over IP, music, TV, etc), and others.
