Communication standard -- communication protocol

1. What is an agreement

From the perspective of application , The agreement can be understood as “ The rules ”, It's the rules of data transmission and data interpretation .
hypothesis ,A、B Both parties want to transfer documents . Regulations ：
for the first time , Transfer file name , The receiver received the file name , The reply OK To the sender ;
The second time , The size of the sent file , After receiving the data, the receiver replies again OK;
third time , Transfer file content . Again , After receiving the data, the receiver will reply OK Indicates that the file content was received successfully .
thus , No matter what A、B What kind of files are passed between , It is completed through three data transmissions .A、B The simplest data transmission rule is formed between . Both parties send... According to this rule 、 receive data .A、B The mutual rule reached between them is the agreement .
This is only in A、B The agreement to be observed between them is called the original agreement . When this agreement is adopted by more people , Constantly increasing 、 improvement 、 maintain 、 perfect . Eventually form a stable 、 Complete file transfer protocol , It is widely used in various file transmission processes . The protocol becomes a standard protocol . One of the earliest ftp The agreement is derived from this .
TCP The protocol focuses on data transmission .http The protocol focuses on the interpretation of data .

Typical protocol

Transport layer Common protocols are TCP/UDP agreement .
application layer Common protocols are HTTP agreement ,FTP agreement .
The network layer Common protocols are IP agreement 、ICMP agreement 、IGMP agreement .
Network interface layer Common protocols are ARP agreement 、RARP agreement .
TCP Transmission control protocol （Transmission Control Protocol） It's a connection oriented 、 reliable 、 Transport layer communication protocol based on byte stream .
UDP User datagram protocol （User Datagram Protocol） yes OSI A connectionless transport layer protocol in the reference model , Provide simple and unreliable transaction oriented information transfer services .
HTTP Hypertext transfer protocol （Hyper Text Transfer Protocol） It is the most widely used network protocol on the Internet .
FTP File transfer protocol （File Transfer Protocol）
IP Protocol is internet protocol （Internet Protocol）
ICMP Agreement is Internet Control message protocol （Internet Control Message Protocol） It is TCP/IP A sub protocol of the protocol family , Used in IP host 、 Routing control messages between routers .
IGMP Agreement is Internet Group management protocol （Internet Group Management Protocol）, It is a multicast protocol in the internet protocol family . The protocol runs between the host and the multicast router .
ARP The protocol is a forward address resolution protocol （Address Resolution Protocol）, Through what is known IP, Find the corresponding host MAC Address .
RARP It's reverse address translation protocol , adopt MAC Address determination IP Address .

ttl Through a router minus 1, Default 64 perhaps 128