OSI model, TCP/IP model:
1. The origin of the OSI model:
During the development of the network, each country and region developed its own network independently, but when the network was interconnected, it was found that the interconnection was not possible due to inconsistent standards.
In order to solve the problem of inconsistent standards,
ISO (International Organization for Standardization) produces a standard for the field of network communication: OSI (Open Systems Interconnection Reference Model).
Suggestion: Any manufacturer in the industry should follow a unified standard when developing software and hardware, so as to realize the network interconnection of each country.
The OSI model is divided into 7 layers according to different functions.
Example: A set of systems when sending express delivery is : Cargo——Express Brother——Transportation Department——Sending Brother——Receive
1) The name of the seven layers: material data network transmission meeting expression response
application layer
presentation layer
session layer
transport layer
Network layer
data link layer
physical layer
2) Functions of each layer of the seven layers of O SI - express delivery example
Application layer --------- data generation - mobile phone
Presentation layer--------package data----package
Session layer -------- establish a session --- contact the courier brother
Transport layer --- data transmission method --- select logistics company
Network layer ------ define logical address, route selection --- fill sender's address and receiver's address on the courier list
Data Link Layer—Physical Address-----The area experienced by express delivery during transportation
Physical layer --- physical road for data transmission --- express transportation road
3) Use of Kelai tools
Purpose: To see if the data is hierarchical in the network
The layers that can be seen are: data link layer, network layer, transport layer
Software use:
Install the software --- use the software:
4、TCP/IP：
1. TCP/IP five-layer model:
application layer
transport layer
Network layer
data link layer
physical layer
1 ) Network layer:
-- IP: Internet Protocol
--ICMP: Internet Control Message Protocol
--ARP: Address Resolution Protocol
-- OSPF protocol : open shortest path first protocol
2) Transport layer:
--TCP: Transmission Control Protocol
--UDP: User Datagram Protocol
3 ) Application layer:
--HTTP: Hypertext Transfer Protocol TCP 80
--FTP: File Transfer Protocol TCP 21, 20
--TFTP: Trivial File Transfer Protocol UDP 69
-- DHCP : Dynamic Host Configuration Protocol UDP 67 68
5. What is data communication
Communication between devices refers to the ability of devices to transmit data to each other
The data transmission of the device time must be bidirectional, and each direction is divided into 3 stages
① Generate data (data encapsulation)
② Data transmission (network transmission)
③ Receive data (data decapsulation)
5. Encapsulation and decapsulation of data
1. How to package?
1) Add the header information of each layer in front of the data (packaging) 1
2. How to unpack?
1) When reaching each layer, the header information of the corresponding layer will be removed (unpacking)
6、PDU
1) protocol data unit - protocol data unit
2) When the data generated by the application is transmitted in the TCP/IP model, it has a different name at each layer, also called PDU
3) In the application layer --- data flow
4) In the transport layer --- data segment
5) At the network layer --- data packets
6) In the link layer --- data frame
7) At the physical layer --- bit stream (lots of 0s and 1s)
7. Correspondence between equipment and layers :
Therefore, the next step is to analyze layer by layer:
8. Physical layer
cable
Twisted pair: Category 5, Super 5, Category 6 -----Enterprise use
Cat6e, Cat7e, Cat8-----data center
Connector: crystal head
Crystal head/free crystal head
information panel
Network pliers
Test Leads / Tracers
cable management rack
patch panel
Cabinet (network cabinet/server mechanism) [height/depth/width/heat dissipation/weighing]
1U=4.45CM refers to the height
optical fiber
Single mode - long-distance transmission
Multimode - for short-distance transmission
Wireless Medium: Electromagnetic Waves
Fiber optic connector
Optical Fiber Fusion Splicer
fiber optic module
Fiber Tester
9. Data link layer
1. The functions of the data link layer are
Mainly: how to combine data into data blocks (this data block is called a frame in the data link layer, and the frame is the transmission unit of the data link layer); how to control the transmission of frames on the physical channel, including how to process Transmission errors, how to adjust the sending rate to match the receiver; provide data link establishment, maintenance and release management between two network entities
2. There are the following problems and solutions when sending data in Ethernet:
1) How the host distinguishes whose data comes from
MAC Globally unique address, physical address, network card address.
- The composition of the MAC address:
The first 24bit (manufacturer number) + the last 24bit (the network card number produced by the manufacturer), a total of 48bit (bit represents 0 or 1)
But in the first 24bit (manufacturer number)
When the 8th bit is 0: it means that it is a physical network card (one network card in unicast corresponds to one device/host)
When the 8th bit is 1: it means that it is a logical network card (multicast is a virtual network card, representing one network card to multiple devices)
- MAC representation method:
-- Use hexadecimal method to represent
- Whether the host can understand the data sent by the other party
① The Ethernet data frame used, the format of the data frame and the function of each field:
Destination address: the MAC address of the receiving host
Source address: MAC address of the host sending data
6 bytes: length of a MAC address (8 bits = 1 byte 6 bytes * 8bit = 48bit)
Type: Indicates what protocol the upper layer uses when processing data, and it is marked at the second place
Data: the number sent by the user---picture text document
Frame check sequence: it is used for checking, mainly to check whether the data is damaged, and if the data is good, it will be received
The data is in the data frame: (just understand)
What is the maximum: 1500 bytes
What is the minimum: 46 bytes
What is the maximum size of the entire data frame: 6+6+2+1500+4 =1518 bytes
What is the minimum size of the entire data frame: 6+6+2+46+4=64 bytes
