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This article mainly explains the "detailed introduction of the layer 7 protocols of the PHP network". The content of the explanation in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "the detailed introduction of the layer 7 protocols of the PHP network".

What are the network layer 7 protocols?

(traditional layer 7) OSI layer (layer 7): physical layer, data link layer, network layer, transport layer, session layer, presentation layer, application layer.

TCP/IP layering (layer 4): network interface layer, internetwork layer, transport layer, application layer.

Five-layer protocol (layer 5): physical layer, data link layer, network layer, transport layer, application layer.

The agreement for each layer is as follows:

Physical layer: RJ45, CLOCK, IEEE802.3 (repeater, hub)

Data links: PPP, FR, HDLC, VLAN, MAC (bridge, switch)

Network layer: IP, ICMP, ARP, RARP, OSPF, IPX, RIP, IGRP, (router)

Transport layer: TCP, UDP, SPX

Session layer: NFS, SQL, NETBIOS, RPC

Presentation layer: JPEG, MPEG, ASII

Application layer: FTP, DNS, Telnet, SMTP, HTTP, WWW, NFS

The functions of each layer are as follows:

Physical layer: transmission of bits through the media to determine mechanical and electrical specifications (bit Bit)

Data link layer: assembles bits into frames and point-to-point delivery (frame Frame)

Network layer: responsible for packet delivery from source to destination and Internet interconnection (packet PackeT)

Transport layer: provides reliable end-to-end message delivery and error recovery (segment Segment)

Session layer: establishing, managing, and terminating sessions (session protocol data unit SPDU)

Presentation layer: translating, encrypting, and compressing data (representing protocol data unit PPDU)

Application layer: means of allowing access to the OSI environment (application protocol data unit APDU)

The difference between TCP and UDP?

TCP provides connection-oriented and reliable data flow transmission, while UDP provides non-connection-oriented and unreliable data flow transmission.

The TCP transmission unit is called the TCP segment, and the UDP transmission unit is called the user Datagram.

TCP pays attention to data security, UDP data transmission is fast, because there is no need for connection waiting, a lot of less operations, but its security is general.

Protocols corresponding to TCP and protocols corresponding to UDP

Protocols corresponding to TCP:

(1) FTP: defines the file transfer protocol and uses port 21.

(2) Telnet: a port for remote login. Using port 23, users can connect to the computer remotely under their own identity and provide communication services based on DOS mode.

(3) SMTP: Mail transfer protocol for sending mail. The server opens port 25.

(4) POP3: it corresponds to SMTP, and POP3 is used to receive mail. The POP3 protocol uses port 110.

(5) HTTP: a transfer protocol for transferring hypertext from a Web server to a local browser.

Protocols corresponding to UDP:

(1) DNS: used for domain name resolution service to convert domain name addresses into IP addresses. DNS uses port 53.

(2) SNMP: simple Network Management Protocol, using port 161, is used to manage network devices. Due to the large number of network devices, connectionless services show their advantages.

(3) TFTP (Trivial File Transfer Protocal), a simple file transfer protocol that uses UDP services on well-known port 69.

TCP/IP has a total of four layers: application layer, transport layer, network layer, and network interface:

Application layer: various services and applications use the network through this layer, commonly used protocols: HTTP,FTP,SMTP

Transport layer: confirm data transmission for error correction, commonly used protocol: TCP UDP

Network layer: responsible for data transmission, path and address selection, commonly used protocols: IP ARP (address Resolution Protocol)

Network interface: Erthernet is a protocol for connection forms of different physical networks.

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