1. CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002

2. February 5, 2002CE80N -- Lecture #102 General Information TA Office… –Trailer #15 is no more –Moved to the ISB –The Interdisciplinary Sciences Building (ISB) is across McLaughlin Drive and to the southeast of Baskin Engineering. It's about a 5 minute walk from BE. URL below is campus map with ISB shown. http://www.ucsc.edu/general_info/images/map- campusBW-lg.gif http://www.ucsc.edu/general_info/images/map- campusBW-lg.gif

3. Chapter 20

4. February 5, 2002CE80N -- Lecture #104 Electronic Mail The first “Killer App”… Allowed users to communicate via computer – asynchronously Modern day GUIs hide original “command line” operation Uses client-server architecture

5. February 5, 2002CE80N -- Lecture #105 Description Of Functionality Electronic mail systems permit complex communications and interactions. –Send a single message to many recipients –Send a message that includes text, audio, video, or graphics –Send a message to a user on a network outside the Internet –Send a message to which a computer program responds

6. February 5, 2002CE80N -- Lecture #106 The Best Of All Worlds Networks provide the speed of telephone communication and permanence of postal mail. –Can transfer small notes or large documents Caveat: there are size limitations on email attachments at some sites –Have become extremely popular

7. February 5, 2002CE80N -- Lecture #107 Each User Has A Mailbox For E- mail Like a post office mailbox, each e-mail mailbox has an address. Any user can send e-mail to another user if they know the mailbox address. Only the owner of the box can open the mailbox – but others can snoop the mail while enroute.

8. February 5, 2002CE80N -- Lecture #108 Sending An E-mail Message To send e-mail across the Internet, the user: –Runs an e-mail application –Composes and edits a message Adds attachments –Specifies a recipient –Finishes entering the message –Sends the message Hey, where’s the send button?

9. February 5, 2002CE80N -- Lecture #109 EMAIL Attachments Attachments are not added strictly “as- is” –Must be converted to text only characters for proper operation in mail servers. –Attachments are encoded using a well known method: MIME: (Multipurpose Internet Mail Extensions) BinHex: Macintosh systems UUENCODE: Unix systems and PCs

10. February 5, 2002CE80N -- Lecture #1010 Notification That E-mail Has Arrived A user can configure the e-mail software to: –Print text messages when mail arrives “You’ve got mail” –Play a recording or tone when mail arrives “You’ve got mail!” –Set an icon on the screen –Suppress notification altogether

11. February 5, 2002CE80N -- Lecture #1011 Reading An E-Mail Message When the e-mail application begins, it: –Tells the user about waiting messages –Gives an initial summary of the mail –Displays the message contents –Allows the user to: Send a reply Leave the message in the inbox Save the message Delete the message

12. February 5, 2002CE80N -- Lecture #1012 E-mail Messages Look Like Interoffice Memos An e-mail message begins with a header: From: To: Date: Subject :

13. February 5, 2002CE80N -- Lecture #1013 E-mail Software Fills In Header Information User-friendly software hides unnecessary header lines when displaying an e-mail message. See the example below: Received: from amazon.com ([208.33.217.124]) by company1.com with Microsoft SMTPSVC(5.5.1877.447.44); Sat, 3 Jun 2000 12:14:03 -1000 Received: by amazon.com id OAA04950; Sat, 3 Jun 2000 14:28:33 -0700 (PDT) Date: Sat, 3 Jun 2000 14:28:33 -0700 (PDT) Message-Id: X-AMAZON-TRACK: john_doe@company1.com X-AMAZON-TRACK-2: fathers-day-4 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary=amazon From: Amazon.com Subject: Save $25 at Amazon.com's New Tools & Hardware Store To: john_doe@company1.com Return-Path: meercat-bounces@bounces.amazon.com

14. February 5, 2002CE80N -- Lecture #1014 How E-mail Works E-mail systems follow the client server approach. –Cooperate to send an email message From sender to recipient’s mailbox Sender’s computer is the client –Contacts an e-mail server program on the recipient’s computer –Stores the message in the recipient’s mailbox

15. Figure 20.1 Figure 20.1 An e-mail transfer across the Internet requires two programs: a client on the sender’s computer and a server on the recipient’s computer.

16. February 5, 2002CE80N -- Lecture #1016 Using E-mail From A Personal Computer Most personal computers do not receive e-mail directly. –Arrange to have a mailbox on a large computer (I.e, at the ISP) –Contacts the main computer system Mail program: Eudora, Netscape, etc… –Obtains a copy of their mailbox

17. February 5, 2002CE80N -- Lecture #1017 EMAIL remote operation w/PCs Mail Server A Mail Server B Sender A Recipient B

18. February 5, 2002CE80N -- Lecture #1018 Mailbox Address Format Addresses consist of a string of characters separated by the “@”. john_doe@sales.company.com The prefix: –identifies the user. The suffix: – gives the domain name of the computer on which the user’s mailbox resides.

19. February 5, 2002CE80N -- Lecture #1019 Abbreviations Make E-mail Friendly Most e-mail systems allow a user to define abbreviations for the mailbox address. For example: venus.engineering.somecompany.com Becomes eng Allowing the address of jane@eng jane@eng (Instead of jane@venus.engineering.somecompany.com)

20. February 5, 2002CE80N -- Lecture #1020 Aliases Permit Arbitrary Abbreviations Most commercially available software supports an e-mail alias. –Requires the user to prepare a list of aliases –Translates the alias to a longer e-mail address ‘mary’ can be used in place of: –mary_doe@company2.somewhere.com

21. February 5, 2002CE80N -- Lecture #1021 Aliases Shared By All Users Of A Computer System System-wide aliases make it possible for all users to share abbreviations. –Consider these: Webmaster Listmanager Help Printers

22. February 5, 2002CE80N -- Lecture #1022 Sending To Multiple Recipients E-mail systems allow users to send messages to multiple recipients. –Specify multiple mailbox addresses on the ‘To’ line of message For example: –To: bob@bedrock.com, bev@mars.combob@bedrock.combev@mars.com

23. February 5, 2002CE80N -- Lecture #1023 Mailing List: An Alias for Multiple Recipients A mailing list is an e-mail alias that specifies multiple recipients The system: –Sends a message to the alias –Delivers a copy to each recipient on the list

24. February 5, 2002CE80N -- Lecture #1024 Public Mailing Lists And Mail Exploders A public list permits a user on any computer connected to the Internet to send a message to a list of recipients. When the e-mail message reaches the destination computer, an exploder: –Finds the name –Expands the abbreviation –Forwards a copy to each recipient

25. Figure 20.2 Figure 20.2 The path of a mail message sent to a public mailing list that contains three recipients. A Mail exploder retrieves the message, and forwards a copy to each recipient on the list.

26. February 5, 2002CE80N -- Lecture #1026 E-mail To And From Non- Internet Sites E-mail can be forwarded to other networks. For example, Compuserve: –Does not use the same Internet protocols –Uses software on an intermediate computer to send and receive Internet e-mail

27. February 5, 2002CE80N -- Lecture #1027 Access To Services Via E-mail A computer program can: –Be used to answer and reply to an e- mail message. An e-mail message can: –Be used to provide access to a variety of remote services.

28. February 5, 2002CE80N -- Lecture #1028 Speed, Reliability, And Expectations E-mail systems are more reliable than postal mail systems. –Delivery is usually within minutes –Sender is notified if a message cannot be delivered Not all homes have computers connected to the Internet. Differences in expectations can make e- mail frustrating. –Not all users read their email at the same rate

29. February 5, 2002CE80N -- Lecture #1029 Impact And Significance Of Electronic Mail After using it, email benefits become apparent. –Combines benefits of instantaneous communication with freedom from interruption –Provides a way for groups to share common interests –Can communicate with more people

30. February 5, 2002CE80N -- Lecture #1030 Joining A Mailing List To join a list, the user must send a request via e-mail. The request is not sent to the list but to a second alias used for joining or leaving a list. –To join: movies@cinema.orgmovies@cinema.org –Email to: movies-request@cinema.orgmovies-request@cinema.org

32. February 5, 2002CE80N -- Lecture #1032 Glossary Electronic Mail –(Email) A service that permits one to send a memo to another person, a group, or a computer program. Mail Alias –A synonym for email alias.

33. February 5, 2002CE80N -- Lecture #1033 Glossary Mailbox –A storage area, usually on disk, that holds incoming e-mail messages until a user reads the mail. Mailbox Address –A synonym for e-mail address.

34. February 5, 2002CE80N -- Lecture #1034 Glossary Mailing List –An electronic mail address that includes a list of recipients. Postmaster –By convention, an e-mail alias for the person who manage the electronic mail software on a given computer.

35. February 5, 2002CE80N -- Lecture #1035 Glossary Smiley –A sequence of characters, usually found in an e-mail message, that indicates humorous intent. The three character sequence :-) resembles a smiling face turned sideways. POP –Abbreviation for Post Office Protocol.

36. Midterm Results

37. February 5, 2002CE80N -- Lecture #1037 Midterm Results 50 questions –High score: 48 = 96% –Low score: 23 = 46% –Median: 38.4 = 76.8% –Passing grade >= 30

38. February 5, 2002CE80N -- Lecture #1038 Most missed questions #11, (77): Prefix bits #38, (73): Routing protocol #30, (60): LAN technologies #19, (56): IP layer #27, (55): Distributed computing #10, (54): CIDR network bits #32, (54): Packet switching

39. February 5, 2002CE80N -- Lecture #1039 Question #11 11) How many prefix bits (network bits in CIDR) are contained in the Class A address 10.0.0.0 a. 32 b. 24 c. 16 d. 8  Class A has a fixed prefix of 8 bits e. 10

40. February 5, 2002CE80N -- Lecture #1040 Question #38 38) The Routing Information Protocol (RIP) only communicates routing information with its directly attached neighbors. RIP is an example of what type of routing protocol? a. Link state b. Round-robin c. Distance vector  RIP is distance vector d. Service oriented

41. February 5, 2002CE80N -- Lecture #1041 Question #30 30) LAN Technologies, in general are: a. Not Compatible  LANs are not compatible b. Highly interoperable c. Proprietary d. Plug and Play

42. February 5, 2002CE80N -- Lecture #1042 Question #19 19) IP resides in what layer of the protocol stack (Berkeley or OSI) a. Routing layer b. Transport layer c. Link layer d. Network layer  IP is in the network layer e. Physical layer

43. February 5, 2002CE80N -- Lecture #1043 Question #27 27) Any interaction that involves two or more computers over a network is called: a. Local communication b. Distributed computing  c. True networking d. Universal service

44. February 5, 2002CE80N -- Lecture #1044 Question #10 10) Based on CIDR addressing, how many network bits are contained in the address range 128.114.100.0/20 a. 128 b. 0 c. 100 d. 20  CIDR network bits

45. February 5, 2002CE80N -- Lecture #1045 Question #32 32) Packet switching is more efficient than circuit switching because of a. Faster router speeds b. Resource sharing  c. Short packets are always used d. Ethernet LANs e. All of the above

46. February 5, 2002CE80N -- Lecture #1046