CE80N Introduction to Networks & The Internet

1. CE80NIntroduction to Networks&The Internet Dr. Chane L. Fullmer UCSC Winter 2002

2. Class Information • Web page tutorial available on-line • Web page submission: • Email to venkat@cse.ucsc.edu • Subject: cmpe080n-assgn4 • Must be emailed on or before March 15 • No extensions can be granted – don’t be late • Final Exam • Last class session • March 14, 2002 • Similar to midterm – open notes/open book CE80N -- Lecture #17

3. Personal Web Page of the Day • A few brave souls…. • Presenting: • http://members.cox.net/fumanstan/ CE80N -- Lecture #17

5. Facsimile (AKA as FAX) • The first facsimile transmission: • 1843 by Alexander Bain’s “Recording Telegraph” • Early fax machines were expensive and proprietary – no interoperation between brands • Used by weather and news services (wire photos) • 1984 – Standardized by the CCITT (The International Telegraph and Telephone Consultative Committee) • Uses basic telephone for interconnections • Today, millions sold annually… • Works globally – where ever there’s a phone. CE80N -- Lecture #17

6. Sending A Fax • The Internet can be used to send a fax. • A document, image, etc. is converted to a file in facsimile format that can be transmitted via a fax modem to the destination fax machine. • A facsimile received via the fax modem from a fax machine is stored as a file that can later be viewed or printed. • C.L. Fullmer, et al “A TCP/IP Network Facsimile System built from publicly available software”, ACM 20th Computer Science Conference, March 1992, Kansas City, Mo. • Why bother? • Automated document retrieval/report generation • Saves money – no long distance/toll charges • Transmits faster than conventional fax • Bandwidth in the Internet connection is often higher than the fixed voice circuit (64kbps) CE80N -- Lecture #17

7. The Internet Used To Copy Files • E-mail or fax can be used to send short notes. • Download should be used to send large volumes of data. • Large documents/images • Audio – CDs • Video clips • Software (ie, Free BSD) CE80N -- Lecture #17

8. Data Stored In Files • Disks hold large volumes of data. • Stores data in files • Collects files together in folders (aka directories) CE80N -- Lecture #17

9. Copying A File • The network can transfer a file from one computer disk to another. • Uses software developed early in ARPANET called file transfer • Uses a protocol called File Transfer Protocol (FTP) • Today, the application software itself is also called ftp. CE80N -- Lecture #17

10. FTP Is Interactive • A user invokes the FTP application. • Presents the user with a prompt • Waits for the user to enter a command CE80N -- Lecture #17

11. Example FTP Commands • Many FTP commands are available. • You only need three simple commands to get a file from a remote machine: CE80N -- Lecture #17

12. A User Can Store Or Retrieve A File • FTP can retrieve (get) a copy of a file. • Contacts a remote computer • Obtains a copy of a file • FTP can store (put) a copy of a file. • Contacts a remote computer • Sends a copy of a file • (Uses the put command, instead of get) CE80N -- Lecture #17

13. Commands For Binary And Text File Format • There are two FTP file formats: • Using text • Text files are not always obvious • Using binary • Non text files may include: • Graphics • Audio • Video • Compressed data text binary CE80N -- Lecture #17

14. Choosing ASCII or Binary Transfer • FTP does not understand the format or contents of a file. • Using the incorrect transfer type results in a malformed copy • Using binary to transfer a file is safer if in doubt ASCII binary CE80N -- Lecture #17

15. Commands For Authorization And Anonymous FTP • A remote FTP service asks users for authorization by: • Prompting for a login identifier • Prompting for a password • Anonymous FTP allows anyone to access public files by: • Entering login of anonymous • Entering password of guest • Sometimes email address is used for password CE80N -- Lecture #17

16. FTP Live Demonstration CE80N -- Lecture #17

17. A Browser Can Use FTP • The URL specifies to the browser to use FTP. • ftp://www.soe.ucsc.edu/classes/cmpe080n/Winter02/lec1.pdf • ftp://ftp.cs.purdue.edu/pub/comer/example • All the details are handled by the browser. • Uses anonymous FTP CE80N -- Lecture #17

18. How FTP Works • FTP uses the client-server approach. • Uses TCP/IP for data transfer • Acting as the client • FTP application software • User’s browser • Acting as the server • Remote computer CE80N -- Lecture #17

19. FTP Client-Server example

20. Impact and Significance Of FTP • FTP data transfer caused more traffic on the early Internet than any other application. • Replaced by Web traffic in 1995 CE80N -- Lecture #17

21. Fax/FTP Summary • Faxes can be converted to files and transported over the Internet • FTP – File Transfer Protocol • Client-Server architecture • FTP is interactive • “Anonymous” FTP for public access to files • Web browsers can use FTP CE80N -- Lecture #17

23. Glossary • Anonymous FTP • Use of the special login anonymous to obtain access to public files through the FTP service. • Binary file • Term is used to refer to nontext files. CE80N -- Lecture #17

24. Glossary • Directory • A collection of files and other directories. Some computer systems use the term folder. • File Transfer Protocol • (FTP) The Internet service used to transfer a copy of a file from one computer to another. CE80N -- Lecture #17

25. Glossary • Folder • A synonym for directory. • Internet FAX • A fax sent across the Internet instead of a conventional telephone connection. • Login • The process of entering an account identifier and password to obtain access to a timesharing computer. CE80N -- Lecture #17

26. Glossary • Password • The secret code a user enters to gain access to a timesharing system or to gain authorization for the FTP service. • Public files • Files that are available to any Internet user. • Text file • Any file that consists of textual characters separated into lines. CE80N -- Lecture #17

28. Early Computers Used Textual Interfaces • When the Internet was being invented, computers consisted of timesharing systems. • Allowed many users to access the system simultaneously • Appeared to operate the same as a personal computer CE80N -- Lecture #17

29. A Timesharing System Requires User Identification • Because multiple users can interact with a timesharing computer, the system requires each user to identify themselves when they begin. • Requires: • a login identifier • a password CE80N -- Lecture #17

30. Remote Login Resembles Conventional Login • Remote login service allows a user to access a remote timesharing computer system. • To use the service, a user: • Invokes an application program • Specifies the name of a remote computer • Provides a login identification • Specifies a password CE80N -- Lecture #17

31. How Remote Login Works • Remote login follows the client-server paradigm. • The client: • Is the application that uses TCP/IP to connect • The server: • Allows the user to interact with the remote computer • Sends output to the client CE80N -- Lecture #17

32. Remote Login Example Figure 28.1 Remote login across the Internet uses two programs. The user invokes an application on the local computer. The local application connects the user’s keyboard and display to the remote timesharing system.

33. Escaping From Remote Login • Client software provides a way for a user to escape and communicate with the local client. • Provides a key on the keyboard to abort a running program • Why do we need it? • An application runs on the remote computer • The remote login client is running on the local computer • If one, or both applications freeze (fail in some way) we have a way to regain control of the local computer system. CE80N -- Lecture #17

34. Displays And Windows • On a computer system using windows, remote login operates as if the window is a small terminal screen. CE80N -- Lecture #17

35. The Internet Remote Login Service Is TELNET • The Internet standard for remote login service is found in a protocol known as TELNET. • Specifies how a remote client and a remote login server interacts • Uses a character oriented interface CE80N -- Lecture #17

36. TELNET Live Demonstration CE80N -- Lecture #17

37. Remote Access Can Display A Desktop • Software can be placed on two computers that displays an exact copy of one computer’s screen on another computer. CE80N -- Lecture #17

38. Remote Desktop Example Figure 28.2 Illustration of a remote desktop service. Software permits the display on a user’s computer to show the screen image from a remoter computer.

39. How Remote Desktops Operate • A remote desktop service operates similar to a remote login service. • Invokes an application • Specifies a remote computer • Takes over the screen, keyboard, and mouse • See: • www.uk.research.att.com/vnc/ CE80N -- Lecture #17

40. Assessment Of Remote Login and Desktops • Internet remote access services are significant for three reasons. • Makes it possible to have computation remote from user • Is significant because of its generality • Is significant because many people use it CE80N -- Lecture #17

41. Generality Makes Remote Login And Desktops Powerful • The power of remote login arises because it provides general access to the program on a computer without requiring program modification. CE80N -- Lecture #17

42. Remote Access Accommodates Multiple Types Of Computers • Remote login service permits arbitrary brands of computers to communicate. CE80N -- Lecture #17

43. Unexpected Results From Remote Access • The user must remember that the application is running on a remote computer. • Cannot print a file using a local printer • Cannot save a file to the local computer • (email of ftp the file to the local computer) CE80N -- Lecture #17

44. Summary • TELNET is the Internet remote login application • Remote login resembles conventional login • Login account and password required • Client-server architecture • TCP/IP used for transport of data CE80N -- Lecture #17

45. Glossary • Login • The process of entering an account identifier and password to obtain access to a timesharing computer. • Remote Desktop • A system that allows a user at one computer to connect their display, keyboard, and mouse to a remote computer. CE80N -- Lecture #17

46. Glossary • Remote Login • A service that allows a user on one computer to connect their keyboard and character-oriented display to a remote computer and run programs. CE80N -- Lecture #17

47. Glossary • TELNET • The Internet remote login service. TELNET allows a user at one site to interact with a remote timesharing system at another site as if the user’s terminal connected directly to the remote machine. • Terminal • A device that enables you to communicate with a computer. Generally, a terminal is a combination of keyboard and display screen. CE80N -- Lecture #17

48. Glossary • Timesharing Computer • A computer system that permits multiple users to run programs at the same time. • Window • A rectangular area on a screen devoted to one particular application program. CE80N -- Lecture #17