OSI seven layer reference model

OSI 7 Layer reference model ：

application layer 、 The presentation layer 、 The session layer 、 Transport layer 、 The network layer 、 Data link layer 、 The physical layer

application layer 、 The presentation layer 、 The session layer ---- Control level
The presentation layer 、 The network layer 、 Data link layer 、 The physical layer ---- Data level

application layer Receive user data , Interface of human-computer interaction , Application oriented

The presentation layer     Change from speaking logical language to machine language , translate , encryption

The session layer     Establish a virtual connection for each kind of data transmitted

Transport layer    effect 1. Distinguish traffic   2. Define the data transmission mode （ Reliable transmission TCP、 Unreliable transmission UDP）

Distinguish traffic by port number
     Common port numbers （<256）：
21 Port number ：FTP File transfer service
22 Port number ：SSH Remote login （ High security Encryption Authentication ）- TCP
23 port ：Telnet Remote login service  TCP
25 port ：SMTP Simple mail transfer service
53 port ：DNS Domain name resolution service  TCP and UDP
80 port ：HTTP Hypertext transfer protocol  TCP
110 port ：POP3 “ Post office protocol version ” Port used
443 port ：HTTPS Encrypted hypertext transfer protocol  TCP
520 port ：RIP   UDP

Port number （portID） , Range of values 1-65535
Static port （ Indicate port ）： Range 1-1023 , characteristic ： The traffic corresponds to the port number one by one and is bound
Dynamic port ： Range 1024-65535, characteristic ： The flow corresponds to the port number one by one

transport ：
TCP: Transmission control protocol , Is a reliable connection oriented transport protocol
UDP: User datagram protocol , It is a non connection oriented unreliable transmission protocol
    TCP： Reliable transmission -- How to ensure reliability ？（1. Acknowledgement mechanism （ Three handshakes ）,2. Retransmission mechanism ）
         data structure ：
    UDP： Transmission is unreliable — characteristic （1. Large flow 2. High real-time performance 3. Insensitive to data loss ）
         data structure ：
         
     Three handshakes ( Make sure PC And server Connect )：
    1.PC Send to server Sync (syn) request (req), request server The port is open , Request to keep in sync with the server ;——PC towards server Make a synchronization request
    2.server to PC reply ACK And synchronization (syn) request (req), confirm PC The port is open ;——server Confirm and report to PC Make a synchronization request ;
    3.PC towards server confirm (ACK)

     Three times mobile phone system ： Ensure connection oriented , Also known as TCP Three foot handshake
     Acknowledgement mechanism ： Show confirmation   Implicit confirmation
     Optimization mechanism ： Flow control mechanism ( Sliding window mechanism ) ; Reorder
     Segmented transmission of data ： When transmitting large data, follow MTU Value for segmented transmission .
    MTU： Maximum transmission unit , The default is 1500 byte , You can modify ( But not recommended )

    PDU： Protocol data unit
    4 layer PDU:segment piecewise Fragmentation ---- Data packets   

The Internet layer   network   Addressing   Addressing

Addressing protocol : IP(IPV4/IPV6)、IPX、apple talk、novell、NSAP
    IPV4（32 Bit binary ） Addressing mode ： Dot decimal （0、1 form ）
       IPV6（128 Bit binary ） Addressing mode ： Bold hexadecimal method
complete IP Address ：IP Address + Subnet mask
IP Address ： Network bit + Host bit  
Address classification ：
    A Class address ： The first is fixed as 0
    0XXX XXXX---0-127（1-126）, The subnet mask defaults to 255.0.0.0
    B Class address ： The first is fixed as 10
    10XX XXXX---128-191, The subnet mask defaults to 255.255.0.0
    C Class address ： The first is fixed as 110
    110X XXXX---192-223, The subnet mask defaults to 255.255.255.0
    D Class address ： The first is fixed as 1110
    1110 XXXX---224-239, The subnet mask defaults to 255.255.255.255
    E Class address ： The first is fixed as 1111
    1111 XXXX---240-255, Scientific research address
     Special address ：
        1、0.X.X.X Invalid address （ Reserved address ）,0.0.0.0 Invalid address , For occupancy
        2、127.0.0.1 Loop address , For local testing
        3、 network number , All hosts are 0, Used to describe a network segment
        4、255.255.255.255 Is a restricted broadcast address  
        5、 All hosts are 1, Directional address
        6、 Local link address ：link-local (169.254.0.0  255.255.00)

     Public address ： Globally unique identification address
     Private address ： Address without unique identification
    10.0.0.0  255.255.0.0
    172.[16,31].0.0 255.255.0.0
    192.168.X(0,255).0 255.255.0.0

Data link layer

The data link layer is divided into LLC layer （ Logical link control sublayer ） and MAC layer （ Media access control sublayer ）
Second floor address ：MAC Address （ Media access control ）-- Physics / Hardware / Burn address
MAC Address structure ：48 Bit binary ,12 Points deducted ( Point and point ) Hexadecimal （ A hexadecimal needs to use 4 A binary representation ）
 eg. points :60-F2-62-3C-E3-53=> terminal host mobile phone The server
    Point and point :60F2.623C.E353=> Connect to the device Router A firewall ASA...

The physical layer    Transmission medium （ The cable 、 wireless ）

The cable ： Coaxial cable 、 Twisted pair 、 Optical fiber
     Coaxial cable
         It is divided into thin cable and thick cable
      Thin cable ： transmission speed 10Mbps, transmission distance 185m
      Thick cable ： transmission speed 10Mbps, transmission distance 500m
     Twisted pair (RJ-45)：
         It is divided into shielding （STP) And unshielded (UTP)—8 A copper wire divides 4 Group , Twisted in two （ Reduce interference ）— transmission distance 100 rice
        568A Linear sequence : White and green 、 green 、 White orange 、 blue 、 White and blue 、 orange 、 White brown 、 Brown
        568B Linear sequence : White orange 、 orange 、 White and green 、 blue 、 White and blue 、 green 、 White brown 、 Brown （ yes 568A Of 3612 Linear sequence ）
       Parallel lines : Also known as the through line , Same line sequence . Parallel lines are used for different layers of equipment .
       Cross line : The line sequence is different . Cross connect line is used for equipment on the same floor .
       All negative : Also known as console Line , Configuration line , The line sequence is opposite , Network equipment for user control .
    Optical fiber
     It is divided into single-mode and multi-mode , Through the optical waveguide ( glass ) Transmit optical signals
Transmitting optical signals requires changing from electrical signals to optical signals ：
  Electrical signals —> optical signal ： Light-emitting diode ( multimode ) or Injection laser diode ( Monomode )
  optical signal —> Electrical signals : Generator diode

wireless :   Infrared 、 microwave 、 bluetooth 、 radio 、wimax
     radio ： standard IEEE 802.11
     bluetooth ： standard IEEE 802.15
    wimax： standard IEEE 802.16
     Global mobile communication system （GSM）
Router ： Third floor equipment , distinguish IP Address .
     It has the function of isolating broadcast domain , An interface is a broadcast domain , Different interfaces are in different network segments ( Broadcast area )
Switch ( bridge )： Second floor equipment , Use MAC Address , All interfaces are in the same broadcast domain by default , An interface is a conflict domain .
A hub (hub)： amplifier Amplify the signal , Belong to 1 Floor equipment , distinguish bit flow ,hub All interfaces on the are in the same conflict domain .