Understanding the TCP/IP protocol

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(5) Application layer

1, function

Application layer is the highest layer of TCP/IP protocol, and it is the level of providing various services for users.

2. Functional understanding

Because of the need for more users on the network, it is difficult to provide all the requirements. Then, provide the corresponding protocol to implement the service.

3. Agreement

(1) FTP (file Transfer Protocol)-----Files Transfer Protocol

File Transfer Protocol is a shared connection of data based on the characteristics of TCP protocol, such as connection-oriented and reliability.

The FTP protocol uses two TCP connections, one is the connection of the control line, the other is the connection of the data line, the control information and the data information are transmitted separately to ensure the correctness and reliability of the data transmission.

(2) Telnet-----telnet protocol

The Telnet protocol is managed by logging on to the server through a remote terminal.

(3) HTTP-----Hypertext Transfer Protocol

It is suitable for hypertext data transmission on the network and the transmission of web pages files.

(4) DNS-----Domain Name System

The use of domain Name System is to make it easy for network users to remember a large number of IP addresses, as long as by remembering a server's domain name as a character form, you can easily access the server's shared resources.

(5) SMTP-----Simple Mail Transfer Protocol

The SMTP protocol provides a message that both sides of the communication are sent online.

(6) POP3-----Electronic Post Office Protocol, third edition

When the two sides of the communication are not on the line, the message is not delivered, then how to meet even if the other side offline can also receive the mail. The current postal system is just one example. With the electronic post Office to temporarily store the sent mail, the receiver can log in to the mailbox to receive mail.

(7) SNMP-----Simple Network Management Protocol

(8) IMAP-----Internet Mail Access Protocol