mạng máy tính nâng cao nguyễn đức thái chương ter7 the application layer sinhvienzone com

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Chapter 7

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The Application Layer

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The DNS Name Space
Resource Records
Name Servers

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DNS – The Domain Name System

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The DNS Name Space

A portion of the Internet domain name space.
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Resource Records

The principal DNS resource records types.
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Resource Records (2)

A portion of a possible DNS database for cs.vu.nl.
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Name Servers

Part of the DNS name space showing the division into zones.
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Name Servers (2)

How a resolver looks up a remote name in eight steps.

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Architecture and Services
The User Agent
Message Formats
Message Transfer
Final Delivery

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Electronic Mail

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Electronic Mail (2)

Some smileys. They will not be on the final exam :-).
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Composition
Transfer
Reporting
Displaying
Disposition

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Basic functions

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Architecture and Services

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The User Agent

Envelopes and messages. (a) Paper mail. (b) Electronic mail.
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Reading E-mail

An example display of the contents of a mailbox.
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Message Formats – RFC 822

RFC 822 header fields related to message transport.
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Message Formats – RFC 822 (2)

Some fields used in the RFC 822 message header.
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MIME – Multipurpose Internet Mail
Extensions

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Problems with international languages:
• Languages with accents
(French, German).
• Languages in non-Latin alphabets
(Hebrew, Russian).
• Languages without alphabets
(Chinese, Japanese).
• Messages not containing text at all
(audio or images).
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MIME (2)

RFC 822 headers added by MIME.
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MIME (3)

The MIME types and subtypes defined in RFC 2045.
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MIME (4)

A multipart message containing enriched and audio alternatives.
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Message Transfer

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Transferring a message
from
to


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Final Delivery

(a) Sending and reading mail when the receiver has a permanent
Internet connection and the user agent runs on the same machine as
the message transfer agent. (b) Reading e-mail when the receiver has
a dial-up connection to an ISP.
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POP3

Using POP3 to fetch three messages.
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IMAP

A comparison of POP3 and IMAP.
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Architectural Overview
Static Web Documents
Dynamic Web Documents
HTTP – The HyperText Transfer Protocol
Performance Ehnancements
The Wireless Web

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The World Wide Web

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Architectural
Overview

(a) A Web page (b) The page reached by clicking on
Department of Animal Psychology.
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Architectural Overview (2)

The parts of the Web model.
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