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The Internet

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. Internet Foundations.

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The Internet

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  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.

  2. 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

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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

  14. Login Names • My account name on WAM is johna • My account name on cs is jra • My account name on dc is ja102001

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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.

  21. 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.

  22. 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.

  23. 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.

  24. 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.

  25. 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.

  26. 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

  27. 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.

  28. 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.

  29. 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.

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