Seven-layer protocol of a network
To understand http, tcp/ip, udp these protocols, we must first understand the seven-layer protocol of the network, the essence of the Internet is a series of network protocols, this protocol is called the OSI protocol. It is the 7 steps of information transmission on the Internet, according to the different functions of the division of labor. In fact, these seven layers do not exist, that is to say, there are no such concepts, and the seven-layer concepts we mentioned today are just artificial divisions. The purpose is just to let everyone better understand what these are used for.
From a professional point of view, OSI is an open communication system interconnection reference model and a well-defined protocol specification. The OSI model has a 7-layer structure, and each layer can have several sub-layers. The 7 layers of OSI from bottom to top are 7-application layer, 6-presentation layer, 5-session layer, 4-transport layer, 3-network layer, 2-data link layer, and 1-physical layer.
In theory, there are 7 layers of protocols, but there are only 4 layers in practical applications. Let’s take a look at the protocols of each layer:
4 layers of protocols: TCP/IP:
data link layer: ARP, RARP
network layers: IP, ICMP, IGMP
Transport layer: TCP, UDP, UGP, ssl
Application layer: http, Telnet, FTP, SMTP, SNMP.
7-layer protocol: OSI protocol
Physical layer: EIA/TIA-232, EIA/TIA-499, V.35, V. 24, RJ45, Ethernet, 802.3, 802.5, FDDI, NRZI, NRZ, B8ZS
Data link layer: Frame Relay, HDLC, PPP, IEEE 802.3/802.2, FDDI, ATM, IEEE 802.5/802.2
Network layer: IP, IPX, AppleTalk DDP
transport layer: TCP, UDP, SPX
Session layer: RPC, SQL, NFS, NetBIOS, names, AppleTalk, ASP, DECnet, SCP
Presentation layer: TIFF, GIF, JPEG, PICT, ASCII, EBCDIC, encryption, MPEG, MIDI, HTML
Application layer: FTP, WWW, Telnet ,NFS,SMTP,Gateway,SNMP
2. How to understand the protocol of each layer
IP is the second layer of the network layer protocol, mainly to determine the sending address, where to send
tcp: it is the third layer protocol, mainly to determine that the route cannot be sent, so there are three tcp handshake
http, ftp, smtp are the fourth layer protocols, The main thing is to carry messages. These agreements are the rules that both parties know and recognize. For example, if you speak English, I also speak English, you speak Chinese, and I also say yes. As long as both parties understand, the rules that both parties understand are called agreements.