OSI and tcp/ip model

OSI ： Open system interconnection （ Reference model ）

OSI The reference model has seven layers , Respectively ：

application layer

The presentation layer

The session layer

Transport layer

The network layer

Data link layer

The physical layer

among , The upper three layers are the control layer , The lower four layers are the data layer .

The following are the functions of each layer ：

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

The presentation layer ： Logic language （ Software language ） Convert to machine language （ Binary language ）, translate , encryption

The session layer ： For each type of data transmitted （ management ： establish 、 maintain 、 End ） A virtual link （ by To prevent different types of data from influencing each other ）

Transport layer ： effect     1. Distinguish traffic               2. Define the data transmission mode

        Use port number to distinguish traffic , Common data transmission methods are TCP and UDP

Port number ： port ID , Range of values 1-65535

Static port ： Also known as port , Range 1-1023

Dynamic port ： Range 1024-65535

Common port numbers ：

HTTP---80  TCP

HTTPS ---443  TCP

RIP----520  UDP

Telnet--- Remote login service   23    TCP

SSH ---- Remote login （ High security    encryption   authentication ）,22  TCP

DNS---- Domain name resolution ,53   TCP and UDP

Unreliable transmission mode and flow characteristics ：1. Large flow   2. High real-time performance   3. Insensitive to data loss

reliable ： How to ensure reliability ？ 1. Acknowledgement mechanism   2. Retransmission mechanism

TCP： Transmission control protocol , Is a reliable connection oriented transport protocol

UDP： User datagram protocol , It is a non connection oriented unreliable transmission protocol

Three times mobile phone system ： Ensure connection oriented , Also known as TCP Three handshakes of

Acknowledgement mechanism ： Explicit 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 ）.

【 notes 】 Units in the Internet  

Bit---- The bit , A binary ,

1000bit=1kbit

1000kbit=1mbit

1000mb=1gb

1000gb=1tb

1000tb=1pb

1000pb=1eb

Byte--- byte , A byte is 8 individual bit

1000B=1KB

1000KB=1MB

1000MB=1GB

1000GB=1TB

Byte   1B   bit   1b    100B   100b

1000======

1024 1024  -----

File storage ----  file system  

1GB    1Gb

Rate unit ： 100Mbps =  100 mega   The bit   Per second   

100M=   12.5MBps

Units in the Internet ： 

①Bit---- The bit , A binary ,

1000bit=1kbit

1000kbit=1mbit

1000mb=1gb

1000gb=1tb

1000tb=1pb

1000pb=1eb

②Byte--- byte , A byte is 8 individual bit ,    Natural language ----  code

1000B=1KB

1000KB=1MB

1000MB=1GB

1000GB=1TB

③ Rate unit ： 100Mbps =  100 Megabits per second    （100M=   12.5MBps）

PDU： Protocol data unit

4 layer PDU：segment  piecewise   Fragmentation

The network layer ：network    effect ：① Addressing     ② Addressing

Addressing protocol ：① IP（IPV4&IPV6）  ② IPX  ③apple talk   ④novell  ⑤NSAP

                at present ,IP Address is the most widely used

IPv4： use 32 Binary addressing

A binary be called 1 Bit or 1bit

        The way of writing ： dotted decimal （ take 32 Bit binaries are divided into four groups , With "." Separate , To facilitate writing ）

eg：1011 0001.0011 1000.0100 0101.0011 1100

        177.56.69.60

IP Address ：32 It's binary ,0 and 1 constitute be used for Addressing

Network mask ：32 It's binary , Successive 1+ Successive 0 constitute , Successive 1 Represents the network bit , Successive 0 Represents the host bit .

               Network bit                      Host bit

1101 1000.0001 0001.0000 0001.0000 0001

216.17.1.1

255.255.0.0

1111 1111.1111 1111.0000 0000.0000 0000

Write a complete IP Address time ：IP Address + Network mask

Address classification ：

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

A Class address ： The first is fixed as 0

0XXX XXXX ---0-127（1-126）, The netmask defaults to 255.0.0.0    

B Class address ： The first two are fixed as 10

10XX XXXX---128-191, The netmask defaults to 255.255.0.0

C Class address ： The first three are fixed 110

110X XXXX---192-223, The netmask defaults to 255.255.255.0

D Class address ： The first four are fixed as 1110

1110 XXXX---224-239, Multicast address , No mask

E Class address ： The first four are 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 （ placeholder ）

2.127.0.0.1 Local testing （127.X.X.X Address of the test ）

3. network number , The network bit remains unchanged All hosts are 0 The address of （ Describe a network segment ）

162.1.1.1------------------162.1.0.0 255.255.0.0

255.255.0.0

4. Restricted broadcast address ,255.255.255.255 

5. directional （ direct ） Broadcast address , The network bit remains unchanged , All hosts are 1

200.1.1.1                 --->    200.1.1.255

255.255.255.0

6. Local link address ：link-local  { 169.254.0.0   255.255.0.0 }

Public address ： Globally unique identification address

Private address ： Address without unique identification

10.0.0.0  255.0.0.0 

172.{16-31}.0.0  255.255.0.0

192.168.X(0-255).0  255.255.255.0

Three layers PDU：packet package

A B C Class addresses are called unicast addresses

unicast ： One to one transmission

Multicast ： One to many transmission

radio broadcast ： One to all transmission modes

Data link layer ： LAN （ Ethernet   Ethernet） 

                     Wide area network   （PPP HDLC ATM FR ）

Second floor address ：Mac Address （ Media access control ）--- Physical address   Hardware address    Burn address

LLC layer ： Logical link control sublayer

MAC layer ： Media access control sublayer

Mac Address structure ： 48 It's binary , Writing uses 12 individual Hexadecimal （ A hexadecimal needs to use 4 individual Binary representation ） The way of writing ： Subtractive hexadecimal or dotted hexadecimal

60-F2-62-3C-E3-53------- terminal   host mobile phone   The server

60F2.623C.E353------- Connect to the device      Router A firewall   ASA etc.

front 24 position ： manufacturer ID ----OUI（ Uniform resource identifiers ）

after 24 position ： product ID ----interface ID （ Interface identifier ）

On the second floor PDU ：frame  frame

The physical layer ： Pay attention to the mechanical characteristics of network hardware 、 Optical properties 、 Electrical characteristics

First floor PDU：bit        Bit stream

Transmission medium ： Optical fiber    、 Twisted pair （RJ45）

Twisted pair ：

568A Linear sequence ： Green and white 、 green 、 Orange white 、 blue 、 Bluish white 、 orange 、 Brown and white 、 Brown

568B Linear sequence ： Orange white 、 orange 、 Green and white 、 blue 、 Bluish white 、 green 、 Brown and white 、 Brown

Different according to the line sequence , Twisted pair is divided into the following three types ：

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 lines are 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 .

According to the structure , Twisted pair is divided into ： Shielded twisted pair （STP） & Unshielded twisted pair （UTP）

Classify according to the twist ：3 class 4 class （10Mbps） 

                                5 class super 5 class （100Mbps）

                                6 class super 6 class   （1000Mbps-- stay 6 Class line 8 Roots are used at the same time ）

TCP/IP Model ： OSI A model is a theoretical model , In the actual network architecture , It's often hard to do , So a simplified version of the model appeared ——TCP/IP

application layer （ Corresponding OSI Application layer in The presentation layer The session layer ）

Host to host layer （ Transport layer ）

The Internet layer （ The network layer ）

Network interface layer （ Data link layer   The physical layer ）

Data encapsulation ： The process of generating data （ From top to bottom ）

Data unpacking ： The process of receiving data for reading （ From bottom to top ）