[Computer network] application layer

Computer network application layer

Some terms

www

http

html

dns

bootp

dhcp

smtp

pop3

Imap3

Psw

Application layer network service type

6

Network service model

WWW

HTML

URL

DNS

name domain system

Why use DNS

Working Mechanism

Two issues

HTTP

web server

effect

working principle

FTP

Network service model

port

Operating mode

Email

protocol

send

SMTP simple message transport protocol 端口 25

receive

POP3 post office protocol port 110

IMAP internet message access protocol port 143

The process of sending mail

Using the SMTP protocol

1. The message is transmitted to the sender's mail server on
2. Message is transferred to the recipient's mail server until the recipient is removed

Process the message was received

POP3 or IMAP protocols

1. When recipients view the messages, mail client and mail server connection
2. The server will not read the message back to the client

format

Neck

Message body (message)

Data encoding method --Base64

IP address shortage solution