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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

CE80NIntroduction to Networks&The Internet

Dr. Chane L. Fullmer


Winter 2002

general information
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

electronic mail
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

description of functionality
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

the best of all worlds
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

each user has a mailbox for e mail
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

sending an e mail message
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

email attachments
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

notification that e mail has arrived
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

reading an e mail message
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

e mail messages look like interoffice memos
E-mail Messages Look Like Interoffice Memos
  • An e-mail message begins with a header:

From: To: Date: Subject:

CE80N -- Lecture #10

e mail software fills in header information
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 ([]) 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: <[email protected]>

X-AMAZON-TRACK: [email protected]

X-AMAZON-TRACK-2: fathers-day-4

MIME-Version: 1.0

Content-Type: multipart/alternative; boundary=amazon

From: Amazon.com <[email protected]>

Subject: Save $25 at Amazon.com\'s New Tools & Hardware Store

To: [email protected]

Return-Path: [email protected]

CE80N -- Lecture #10

how e mail works
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

figure 20 1
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.

using e mail from a personal computer
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

email remote operation w pcs
EMAIL remote operation w/PCs

Mail Server A

Mail Server B

Sender A

Recipient B

CE80N -- Lecture #10

mailbox address format
Mailbox Address Format
  • Addresses consist of a string of characters separated by the “@”.

[email protected]

  • The prefix:
    • identifies the user.
  • The suffix:
    • gives the domain name of the computer on which the user’s mailbox resides.

CE80N -- Lecture #10

abbreviations make e mail friendly
Abbreviations Make E-mail Friendly

Most e-mail systems allow a user to define abbreviations for the mailbox address. For example:


Becomes eng

Allowing the address of [email protected]

(Instead of [email protected])

CE80N -- Lecture #10

aliases permit arbitrary abbreviations
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

CE80N -- Lecture #10

aliases shared by all users of a computer system
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

sending to multiple recipients
Sending To Multiple Recipients
  • E-mail systems allow users to send messages to multiple recipients.

CE80N -- Lecture #10

mailing list an alias for multiple recipients
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

public mailing lists and mail exploders
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

figure 20 2
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.

e mail to and from non internet sites
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

access to services via e mail
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

speed reliability and expectations
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

impact and significance of electronic mail
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

joining a mailing list
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.

CE80N -- Lecture #10

  • 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

  • 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

  • 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

  • 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

midterm results1
Midterm Results
  • 50 questions
    • High score: 48 = 96%
    • Low score: 23 = 46%
    • Median: 38.4 = 76.8%
    • Passing grade >= 30

CE80N -- Lecture #10

most missed questions
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

question 11
Question #11

11) How many prefix bits (network bits in CIDR) are contained in the Class A address

a. 32

b. 24

c. 16

d. 8  Class A has a fixed prefix of 8 bits

e. 10

CE80N -- Lecture #10

question 38
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

question 30
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

question 19
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

question 27
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

question 10
Question #10

10) Based on CIDR addressing, how many network bits are contained in the address range

a. 128

b. 0

c. 100

d. 20  CIDR network bits

CE80N -- Lecture #10

question 32
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