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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: <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

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 “@”.


  • 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 jane@eng

(Instead of jane@venus.engineering.somecompany.com)

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

      • ‘mary’ can be used in place of:

        • mary_doe@company2.somewhere.com

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.

    • Specify multiple mailbox addresses on the ‘To’ line of message

      • For example:

        • To: bob@bedrock.com, bev@mars.com

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.

    • To join: movies@cinema.org

    • Email to: movies-request@cinema.org

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