OSI architecture and protocols at all levels

OSI Seven layers

7、 ... and 、 application layer

sketch

Realization ⼈ Boundary of machine interaction ⾯

agreement

FTP(FileTransferProtocol, File transfer protocol )

effect

be used for Internet Two way transfer of control files on

Use port number

tcp 20
tcp 21

DNS(Domain Name System, The domain name system )

effect

It is used to IP A distributed database with address mapping , Make it easier for people to access the Internet

Use port number

udp 53

Telnet( Remote terminal protocol )

effect

It provides users with the ability to complete remote tasks on the local computer host Ability to work

Use port number

TCP 23

SMTP(Simple Mail Transfer Protocol, Simple mail transfer protocol )

effect

SMTP It's based on FTP A mail service on file transfer service , It is mainly used for mail information transmission between systems , And provide notice of the letter .

Use port number

tcp 25

HTTP(Hyper Text Transfer Protocol, Hypertext transfer protocol )

effect

It specifies what messages the client may send to the server and what response it will get

Use port number

tcp 80

6、 ... and 、 The presentation layer

sketch

One of its main functions is to provide a common language for heterogeneous communication , For interoperability

code decode encryption Decrypt

agreement

JPEG

MPEG

ASCII

5、 ... and 、 The session layer

sketch

build ⽴ maintain end ⽌ The conversation process

agreement

NFS

SQL

NETBIOS

RPC

Four 、 Transport layer

sketch

Through end ⼝ Number to distinguish different services confirm Retransmission Sort Flow control
Provide end-to-end reliable message transmission and error recovery

agreement

TCP(Transmission Control Protocol, Transmission control protocol )

sketch

A connection oriented 、 reliable 、 Transport layer communication protocol based on byte stream

UDP(User Datagram Protocol, User data protocol )

sketch

A connectionless transport layer protocol , It is mainly used in the transmission which does not require the packet to arrive in sequence , The checking and sorting of packet transmission order is completed by the application layer , Provide simple and unreliable transaction oriented information transfer services

3、 ... and 、 The network layer

sketch

adopt ip Address in ⾏ logical addressing

Try to pass the data from the source through several intermediate node To the destination

agreement

IP(Internet Protocol, IP internet protocol )

sketch

Design IP The goal is to improve the scalability of the network ： One is to solve the Internet problem , To achieve large-scale 、 Interconnection of heterogeneous networks

ICMP(Internet Control Message Protocol)

sketch

Used in IP host 、 Routing control messages between routers

ARP(Address Resoloution Protocol, Address resolution protocol )

sketch

adopt ip Address , obtain mac Address

Two 、 Data link layer

sketch

Assemble bits into frames and point-to-point transmission

agreement

PPP(Point to Point Protocol, Point to point protocol )

sketch

It provides a standard method for uploading and transmitting multi protocol packets on point-to-point connections

One 、 The physical layer

sketch

Create... For the physical links needed to transmit data 、 maintain 、 dismantle , And provide with mechanical , Electronic , Functional and normative features . To put it simply , The physical layer ensures that raw data can be transmitted on a variety of physical media .

agreement

IEEE802.3

sketch

IEEE 802.3 It's a working group , The working group prepared the Institute of electrical and electronics engineers （IEEE） Standard set , The working group defined the media access of physical layer and data link layer of wired Ethernet （mac）