1

The Internet

• Ideas formulated in the early 1960’s.

• Fundamental work done around 1970.

• Some steps involved:– 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

• 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.

3

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

• 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.– 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)

• 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

• 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

• Directories organize files into a hierarchy.• Files contain data and programs.• Path – where something is in the hierarchy.• cd – change directory

– 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

• Type cd ~ja102001

• Type ls -l

• Type more Syllabus

• Type cp Syllabus ~

• Type mail– Read new mail by hitting enter.– Quit mail by typing quit.

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Get project 1

• 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 echo $uid

• Type cd 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.

• Type 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:– ^p move to previous line– ^n move to next line– ^b move left one space– ^f move right one space

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Using pico 4

• ^a move to the start of a line.

• ^e move to the end of a line.

• ^y move up a page.

• ^v move down a page.

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Using pico 5

• Other Commands– ^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 lets you search for text.– ^m inserts a blank line above the

current one.– ^r read in (insert) an external

file.– ^t invoke the spell checker.