Network related knowledge (Hardware Engineer)

LAN （LAN）： LAN is a computer group interconnected by multiple computers in a certain area . Usually within a few kilometers .

Wide area network （WAN）： The wide area network has a wide range , Tens of kilometers to thousands of kilometers , It can be a regional computer network or a national computer network .

The standard of the agreement ：OSI Seven layer model

1、 Physical layer protocol ：

be responsible for 0、1 Bit stream （0/1 Sequence ） And the voltage 、 The transition between wandering flashes . Provides for activation of 、 maintain 、 Turn off the mechanical properties between the communication endpoints 、 Electrical characteristics 、 Functional features and process features ; This layer provides a physical medium for the upper layer protocol to transmit data , Just stating the standard .
In this layer , The unit of data is called bit （bit）（ notes ：bit And bytes Byte, What we often say 1 byte 8 position 2 Base is ：1B=8bit）. Typical specifications for physical layer definitions include ：EIA/TIA RS-232、EIA/TIA RS-449、V.35、RJ-45、fddi Token ring network .

2、 Data link layer protocol ：

Responsible for interconnection at the physical level 、 Communication transmission between nodes （ For example, an Ethernet necklace 2 Communication between nodes ）; The functions of this layer include ： Physical address addressing 、 Data framing 、 flow control 、 Error detection of data 、 Resend, etc .
In this layer , The unit of data is called frame （frame）. Representatives of DLL protocols include ：ARP、RARP、SDLC、HDLC、PPP、STP、 Frame relay, etc .

3、 Network layer protocol ：

Transfer data to the destination address ; The destination address is an address that allows multiple networks to connect through a router , Mainly responsible for finding address and routing , The network layer can also realize congestion control 、 Internet Interconnection and other functions .
In this layer , The unit of data is called a packet （packet）. Representatives of network layer protocols include ：IP、IPX、RIP、OSPF etc. .

4、 Transport layer protocol （ Core layer ）：

The transport layer is OSI The most important of all 、 The most critical layer , It is the only layer responsible for overall data transmission and data control ;
The transport layer provides a mechanism for end-to-end data exchange , Check the group number and order , The transport layer has three layers above it, such as the session layer , Provide reliable transmission service , The main functions of providing reliable destination site information for the network layer . In this layer , The unit of data is called data segment （segment）. The main function ：
①： Providing transport services for end-to-end connections .
②： This transport service is divided into reliable and unreliable , among Tcp It's a typical reliable transmission , and Udp It's unreliable transmission .
③： Provide flow control for end-to-end connections , Error control , Service quality (Quality of Service,QoS) And other management services .
The agreements included are as follows ：
TCP： Transmission control protocol , Low transmission efficiency , High reliability .
UDP： User datagram protocol , It is suitable for low reliability transmission , A small amount of data .
DCCP、SCTP、RTP、RSVP、PPTP Such agreement .

5、 Session layer protocol ：

Responsible for establishing and disconnecting communication connections （ The logical path of data flow ）, Memory data separation and other data transmission related management .

6、 Presentation layer protocol ：

Convert data format to standard format . Convert the information processed by the application into a format suitable for network transmission , Or convert the data from the next layer into a format that the upper layer can process ; Mainly responsible for data format conversion , Ensure that the application layer information of one system can be read by the application layer of another system . say concretely , It is to transform the inherent data format of the device into the network standard transmission format , Different devices may interpret the same bit stream differently ; therefore , Mainly responsible for keeping them consistent .

7、 Application layer protocol ：

①： Hypertext transfer protocol HTTP： This is one of the most basic clients / Server access protocol ; Browser sends request to server , The server responds to the corresponding web page .
②： File transfer protocol FTP： Provide interactive access , Based on the client server model , Connection oriented Use TCP Reliable transportation services . The main function : Reduce / Eliminate file incompatibility under different operating systems .
③： Telnet Protocol TELNET： Client server mode , Can adapt to many differences between computers and operating systems , Network virtual terminal NVT The meaning of .
④： Simple mail delivery protocol SMTP：Client/Server Pattern , Connection oriented . Basic function ： write letters 、 delivery 、 Report transmission 、 Show message 、 The receiver handles the letter .
⑤：DNS Domain name resolution protocol ：DNS Is a method used to convert domain names into IP Address of the Internet service .
⑥： Simple file transfer protocol TFTP： Client server mode , Use UDP The datagram , Only file transfer is supported , No interaction supported ,TFTP Code takes up less memory .
⑦： Simple network management protocol （SNMP）: SNMP Model 4 A component ： Managed node 、 Management station 、 Management information 、 Management Protocol .SNMP agent ： function SNMP The managed node of the management process .
⑧DHCP Dynamic Host Configuration Protocol : Find the boot file name in the protocol 、 Null Terminator 、 Generic name or empty ,DHCP Restricted directory pathname in supply agreement Options – Optional parameter fields , Refer to the selection file in the definition selection list .

PS： In fact, protocol layering is just to better understand the role of my use of protocols , Instead of absolute stratification , Some protocols between layers can also be shared , Especially the session layer 、 Presentation layer and application layer .

Detailed knowledge of various agreements ：https://www.cnblogs.com/fzz9/p/8964513.html