Transcript The Internet

The Internet
• Ideas formulated in the early 1960’s.
• Fundamental work done around 1970.
• Some steps involved:
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Creating the network idea.
Creating the machines to run the network.
Working with different kinds of computers.
Designing generic protocols and interfaces.
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Internet Foundations
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Packet switching instead of dedicated circuits.
Distributed network for reliability.
Machines to route traffic (IMPs).
First network called ARPANET.
Generic Protocols despite different end hosts.
Remote Logins – Telnet.
Remote File Transfer – FTP.
Email and messaging.
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Gateways
• Connect different kinds of networks.
• Data passed between networks is translated
from one network type to another.
• Different Networks:
– Cell Phones
– Wireless Computer Networks
– LANs
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OSI Model
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Open System Interconnection Model
Layer 7: Applications – What you see.
Layer 6: Presentation – Encryption, data ordering.
Layer 5: Session – Connects applications.
Layer 4: Transport – Error correction.
Layer 3: Network – Routing/Switching.
Layer 2: Data Link – Convert data to bits.
Layer 1: Physical – Move the bits using energy.
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Addresses
• Networked computers need names.
• On the Internet, domain names and IP
numbers are used.
• IP is the Internet Protocol, the base protocol
in use on the Internet.
• rac3.wam.umd.edu is a host name.
• rac3.wam.umd.edu also has an IP address:
128.8.10.143
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Domain Names
• Consider rac3.wam.umd.edu.
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The top-level domain is .edu
The domain name is umd.edu
The subdomain is wam.
The machine is rac3.
• Top-level domains include .com, .net, .org, etc…
• Names can be assigned depending on access and
permissions.
• Most domains represent many computers.
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Domain lookup
• nslookup
• whois wam.umd.edu
• whois –h whois.networksolutions.com
wam.umd.edu
• Whois without the middle –h whois.net…
argument will tell which domain server has
the domain information.
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IP Addresses
• Numbers that identify computers on the
Internet.
• Many times assigned in blocks.
• They have 4 numbers.
• Each number is between 0 and 255
inclusive.
• 128.8.10.143 is an IP address.
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Internet Protocol (IP)
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Breaks information into packets.
IP is the “network protocol”.
IP is “unreliable”, no guarantee of delivery.
IP is connectionless – packets can take
different paths.
• Packets may arrive out of order.
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TCP (Transmission Control
Protocol)
• Controls the organization of the
information.
• Provides reliability by ordering packets.
• It resends “lost” packets.
• Duplicates are ignored.
• Checks for transmission errors using a
checksum.
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Other Protocols
• Mail, telnet, ftp, newsgroups, and webpages
all work with different protocols.
• They are protocols on top of TCP/IP.
– Their messages are reliable.
– They add extra data and rules.
– They send specific types of information.
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Ports
• A single machine can listen for many
different types of connections.
• Like different apartment numbers in a
building.
• Telnet is on port 23, ftp on port 21, www on
port 80.
• You can use other ports above 1023 for
special programs.
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Class Cluster Accounts
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Unix Accounts.
On machines called the “detective cluster”.
WAM is at wam.umd.edu
Detective machines are at dc.umd.edu
Names – holmes marlowe marple tracy
wolfe
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Login Names
• My account name on WAM is johna
• My account name on cs is jra
• My account name on dc is ja102001
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Multiple Accounts
• Each account has similar features like
email, but the addresses are different.
• Logging into different accounts means
logging into different machines.
• Each client uses one of a few common
protocols.
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Logging in
• It’s like using your WAM account for mail.
• The command to use to login is called
telnet.
• On Windows click on the start button, then
click on run, then type telnet.
• On a WAM lab UNIX machine type telnet
on any command line.
• If you are on a MAC use NCSA telnet.
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Class Cluster Accounts
• The name of your class account host – the
computer where the class accounts are
stored is dc.umd.edu
• Type o dc.umd.edu
• o can be replaced with open.
• Type your login and password.
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First steps
• Newsgroups will show up. You don’t have
to read this right now. Keep typing q and
space until you exit the news program.
• Your prompt will look like:
%
• Directories are like folders – lists of files.
• Type ls
-- lists the files in a directory.
• Try ls –l Try ls –la Try ls -F
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Directories and files
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Directories organize files into a hierarchy.
Files contain data and programs.
Path – where something is in the hierarchy.
cd – change directory
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cd name
-- go to directory named name
cd ..
-- move up a directory
cd
-- change to home directory
cd ~ja102001
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Help and Logging out
• man
-- gives help on commands.
– There is no “help” command, use man.
• logout -- lets you log off the machine.
• man –k keyword -- gives you a list of
commands that have information about the
keyword, such as man –k password.
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Initial commands
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Type
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cd ~ja102001
ls -l
more Syllabus
cp Syllabus ~
mail
– Read new mail by hitting enter.
– Quit mail by typing quit.
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Get project 1
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Type cd ~ja102001
Type cd project1
Type cp project1.description ~
To print out project 1 for pickup at the AVW
pickup window:
– Type qpr –q prl project1.description
– If you want to use your own printer or the WAM
printers (10cents a page) you may.
– Use lpr project1.description for local printers.
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Setting Up
• Type
~ja102001/setup
• Copy down the project code.
• If you forget your project code
– Type
• Type cd
echo $uid
or type cd ~
– This will send you back to your home directory.
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Using pico 1
• Simple text editor.
• Type pico syllabus
– The file is not there, so the file is blank.
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pico Syllabus
– The file IS there. UNIX is case sensitive.
• You can use arrow keys to move around.
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Using pico 2
• The letter ^ will represent “control”, as in
^x means hold down control and type x.
• Some important commands:
– ^c
(cancel) stops whatever you are doing
and returns you to regular editing.
– ^x quit and save.
– ^o write out (save) the current file. It asks for a
new name.
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Using pico 3
• If you don’t want to use the arrow keys to
move around the screen, you can also use
the following keys:
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^p
^n
^b
^f
move to previous line
move to next line
move left one space
move right one space
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Using pico 4
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^a
^e
^y
^v
move to the start of a line.
move to the end of a line.
move up a page.
move down a page.
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Using pico 5
• Other Commands
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^d
delete current character.
Backspace delete previous character.
^k
delete current line.
^u
pastes last deleted line to current
position.
– ^k and ^u can be combined to copy text.
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Using pico 6
• Some more commands
– ^w
– ^m
current one.
– ^r
file.
– ^t
lets you search for text.
inserts a blank line above the
read in (insert) an external
invoke the spell checker.
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