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CE80N Introduction to Networks & The Internet

CE80N Introduction to Networks & The Internet. Dr. Chane L. Fullmer UCSC Winter 2002. General Information. TA Office… Trailer #15 is no more Moved to the ISB

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CE80N Introduction to Networks & The Internet

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

  2. 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 CE80N -- Lecture #10

  3. Chapter 20

  4. 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 CE80N -- Lecture #10

  5. 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 CE80N -- Lecture #10

  6. 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 CE80N -- Lecture #10

  7. 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. CE80N -- Lecture #10

  8. 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? CE80N -- Lecture #10

  9. 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 CE80N -- Lecture #10

  10. 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 CE80N -- Lecture #10

  11. 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 CE80N -- Lecture #10

  12. E-mail Messages Look Like Interoffice Memos • An e-mail message begins with a header: From: To: Date: Subject: CE80N -- Lecture #10

  13. 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: <OAA06250.200016045128@amazon.com> 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 <tools-news@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 CE80N -- Lecture #10

  14. 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 CE80N -- Lecture #10

  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. 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 CE80N -- Lecture #10

  17. EMAIL remote operation w/PCs Mail Server A Mail Server B Sender A Recipient B CE80N -- Lecture #10

  18. 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. CE80N -- Lecture #10

  19. 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 (Instead of jane@venus.engineering.somecompany.com) CE80N -- Lecture #10

  20. 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 CE80N -- Lecture #10

  21. 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 CE80N -- Lecture #10

  22. 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.com CE80N -- Lecture #10

  23. 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 CE80N -- Lecture #10

  24. 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 CE80N -- Lecture #10

  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. 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 CE80N -- Lecture #10

  27. 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. CE80N -- Lecture #10

  28. 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 CE80N -- Lecture #10

  29. 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 CE80N -- Lecture #10

  30. 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.org • Email to: movies-request@cinema.org CE80N -- Lecture #10

  31. 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. CE80N -- Lecture #10

  32. 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. CE80N -- Lecture #10

  33. 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. CE80N -- Lecture #10

  34. 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. CE80N -- Lecture #10

  35. Midterm Results

  36. Midterm Results • 50 questions • High score: 48 = 96% • Low score: 23 = 46% • Median: 38.4 = 76.8% • Passing grade >= 30 CE80N -- Lecture #10

  37. 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 CE80N -- Lecture #10

  38. 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 CE80N -- Lecture #10

  39. 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 CE80N -- Lecture #10

  40. Question #30 30) LAN Technologies, in general are: a. Not Compatible  LANs are not compatible b. Highly interoperable c. Proprietary d. Plug and Play CE80N -- Lecture #10

  41. 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 CE80N -- Lecture #10

  42. 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 CE80N -- Lecture #10

  43. 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 CE80N -- Lecture #10

  44. 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 CE80N -- Lecture #10

  45. CE80N -- Lecture #10

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