McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Chapter 2 Application Layer.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000

Chapter 2

ApplicationLayer


The client-server paradigm.The client-server paradigm.

Electronic mail.Electronic mail.

File transfer.File transfer.

Remote login.Remote login.

After reading this chapter, the reader should After reading this chapter, the reader should be able to understand:be able to understand:

OOBJECTIVESBJECTIVES

The World Wide Web.The World Wide Web.

Other applications such as videoconferencing and chatting. Other applications such as videoconferencing and chatting.


INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

2.12.1


Figure 2-1

Position of the application layer in the Internet model


CLIENT-SERVERCLIENT-SERVERPARADIGMPARADIGM

CLIENT-SERVERCLIENT-SERVERPARADIGMPARADIGM

2.22.2


Application-layer programs Application-layer programs in the Internet model in the Internet model

communicate using the communicate using the client-server paradigmclient-server paradigm..

Note:Note:


Figure 2-2 Client-server model


Figure 2-3 Client-server relationship


In the client-server In the client-server paradigm, many clients can paradigm, many clients can

be served by one server, be served by one server, either one at a time or either one at a time or

concurrently.concurrently.

Note:Note:


In the client-server In the client-server paradigm, a client runs for paradigm, a client runs for a specific period of time; a specific period of time;

the server runs the server runs continuously.continuously.

Note:Note:


In the client-server In the client-server paradigm, there are specific paradigm, there are specific

servers and normally one servers and normally one general-purpose server. general-purpose server.

Note:Note:


ADDRESSINGADDRESSINGADDRESSINGADDRESSING

2.32.3


Technical Focus:Technical Focus: Domain Name System (DNS)Domain Name System (DNS)

The following are traditional and new domain The following are traditional and new domain names:names:

Traditional: Traditional: com edu gov int net orgcom edu gov int net org

New: New: aero biz coop info museum name proaero biz coop info museum name pro


ELECTRONICELECTRONICMAILMAIL

ELECTRONICELECTRONICMAILMAIL

2.42.4


Email is a store-and-forward Email is a store-and-forward application on the Internetapplication on the Internet..

Note:Note:


A user agent controls the A user agent controls the composing, reading, composing, reading,

forwarding, replying, and forwarding, replying, and saving of email messages. saving of email messages.

The user agent is not The user agent is not responsible for sending or responsible for sending or

receiving email. receiving email.

Note:Note:


The task of sending and The task of sending and receiving email is done by a receiving email is done by a mail transfer agent (MTA).mail transfer agent (MTA).

Note:Note:


The formal protocol for The formal protocol for electronic mail in the electronic mail in the Internet is Simple Mail Internet is Simple Mail Transfer Protocol or SMTP. Transfer Protocol or SMTP.

Note:Note:


Figure 2-4Email delivery


Figure 2-5

POP


Figure 2-6

Email address


Technical Focus:Technical Focus: Inside an Email MessageInside an Email Message

An email is made of an envelope and a letter:An email is made of an envelope and a letter:


Figure 2-7

MIME


Technical Focus:Technical Focus: How MIME worksHow MIME works

MIME has five header types that can be added MIME has five header types that can be added to the original SMTP header:to the original SMTP header:

MIME-VersionMIME-Version

Content-Transfer-EncodingContent-Transfer-Encoding

Content-TypeContent-Type

Content-IDContent-ID

Content-DescriptionContent-Description


FILEFILETRANSFERTRANSFER

FILEFILETRANSFERTRANSFER

2.52.5


Figure 2-8 FTP


GENERAL-PURPOSEGENERAL-PURPOSEAPPLICATION:APPLICATION:

TELNETTELNET

GENERAL-PURPOSEGENERAL-PURPOSEAPPLICATION:APPLICATION:

TELNETTELNET

2.62.6


TELNET is a general-TELNET is a general-purpose client-server purpose client-server application program.application program.

Note:Note:


Figure 2-9

Local login


Figure 2-10

Remote login


WORLD WIDE WEBWORLD WIDE WEB(WWW)(WWW)

WORLD WIDE WEBWORLD WIDE WEB(WWW)(WWW)

2.72.7


Figure 2-11Distributed services


Figure 2-12

Hypertext


Figure 2-13

Browser architecture


Figure 2-14

HTTP transaction


Figure 2-15 Message categories


Figure 2-16

Request and response messages


Figure 2-17

URL


Business Focus:Business Focus: History of WWWHistory of WWW

The idea of the World Wide Web started in 1989 at the European Particle Physics Laboratory, CERN, in Geneva, Switzerland. Tim Bernes-Lee needed to create a large database for physics research, which he found impossible to do using one single computer. The obvious solution was to let each piece of information be stored on an appropriate computer and let the computers be linked together through hypertext.

In 1993, the University of Illinois, under the supervision of Anderson, created the first graphical browser called Mosaic.

In 1994, Anderson and some colleagues started Netscape, one of the most popular browsers today. Another widely used browser is Microsoft Explorer.


Technical Focus:Technical Focus: HTMLHTML

Hypertext Markup Language (HTML) is a language for creating web pages. The term markup language comes from the book publishing industry. Before a book is typeset and printed, a copy editor reads the manuscript and corrects it with marks. These marks tell the designer how to format the text.

For example, to make part of a text displayed in boldface with HTML, we must include the beginning and ending boldface tags (marks) in the text, as shown below:

<B> This is the text to be bold </B>

The two tags <B> and </B> are instructions for the browser.


VIDEOCONFERENCINGVIDEOCONFERENCINGVIDEOCONFERENCINGVIDEOCONFERENCING

2.82.8


Figure 2-18

Videoconferencing


GROUP DISCUSSION:GROUP DISCUSSION:LISTSERVLISTSERV

GROUP DISCUSSION:GROUP DISCUSSION:LISTSERVLISTSERV

2.92.9


Figure 2-19

Listserv


To subscribe, the user To subscribe, the user sends the request to the sends the request to the

subscriber server, not the subscriber server, not the mailer server.mailer server.

Note:Note:


To send an email to every To send an email to every member of the group, the member of the group, the user sends it to the mailer user sends it to the mailer

server, which then server, which then automatically relays it to automatically relays it to

every subscriber.every subscriber.

Note:Note:


CHATTINGCHATTINGCHATTINGCHATTING

2.102.10

McGraw-Hill©The McGraw-Hill Companies, Inc., 2000 Chapter 2 Application Layer.

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