The Application Layer
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Transcript of The Application Layer
![Page 1: The Application Layer](https://reader030.fdocuments.in/reader030/viewer/2022032709/5681303f550346895d95e025/html5/thumbnails/1.jpg)
The Application Layer
Chapter 7
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DNS – The Domain Name System
• The DNS Name Space
• Resource Records
• Name Servers
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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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Electronic Mail
• Architecture and Services
• The User Agent
• Message Formats
• Message Transfer
• Final Delivery
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Electronic Mail (2)
Some smileys. They will not be on the final exam :-).
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Architecture and Services
Basic functions• Composition• Transfer• Reporting• Displaying• Disposition
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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
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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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.