Network metering - application layer

This article mainly introduces the following aspects of knowledge ：

1. Application layer Overview
2. Domain name resolution system DNS
3. File transfer protocol FTP
4. E-mail
5. World Wide Web and HTTP agreement
   

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1. Application layer Overview

(1) Application layer functions

(2) Transport layer model

• C/S Model
  
• P2P Model
  

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2. Domain name resolution system DNS

(1)DNS The function of service

(2) domain name

(3) Domain name server

(4) Domain name resolution process

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3. File transfer protocol FTP

(1) brief introduction

(2) working principle

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4. E-mail

(1) E-mail message format

(2) E-mail System Overview

(2)SMTP agreement

(3)MIME

(4)POP3 agreement

(5)IMAP agreement

(4) E-mail based on the World Wide Web

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5. World Wide Web and HTTP agreement

(1) Overview of the World Wide Web

(2) Hypertext transfer protocol —— HTTP agreement

• summary
  
• characteristic
  
• HTTP Protocol connection mode
  
• HTTP Protocol message structure