Basics of data communication - basic knowledge of network

OSI Reference model

OSI Concept

Open System Interconnect Open Systems Interconnection Reference Model , By ISO（ International Organization for Standardization ） Defined . It's a flexible 、 Robust and interoperable models , It's not an agreement , But a great model . Often used to analyze and design network architecture .

​ OSI Divide the network into seven layers , From bottom to top are The physical layer 、 Data link layer 、 The network layer 、 Transport layer 、 The session layer 、 The presentation layer 、 application layer .

characteristic ：

1. OSI Each layer of the model has its own set of functions ;
2. Layers are independent and dependent on each other ;
3. The top depends on the bottom , The lower level serves the upper level .

OSI Advantages of reference model

• Divide the communication process of the network into smaller ones 、 Simpler parts , therefore Contribute to the development of various components 、 Design and troubleshooting .

• Through network components Standardization , Allow multiple vendors to develop .

• By defining what functions are implemented at each layer of the model , Encourage Industrial Standardization .

• Allow various types of network hardware and software to communicate with each other （ Compatibility ）.

• Prevent changes made to one layer from affecting other layers （ distinct ）, This is conducive to the development .

Data transfer process

Encapsulation of data

De encapsulation of data

Common devices in the network

HUB A hub

• The whole device is in the same conflict domain (collision domain).
• The whole device is in the same broadcast domain ( broadcast domain).
• Device shared bandwidth .

In exchange for Switching

unicast Unicast

Multicast Multicast

radio broadcast Broadcast

Broadcast area Broadcast Domain

Switch （Switch）

• The exchange of data frames
• End user access
• Basic access security functions
• Isolation of broadcast domain （VLAN）
• Redundancy of layer-2 link 、 Anti ring and load sharing

1. Each port of the switch is a collision domain .
2. The whole switch belongs to a broadcast domain .
3. The switch is based on MAC Address .

Router （Router）

• Cut off the broadcast domain 、 Realize data access across three layers
• Routing protocol support 、 Maintain routing tables
• Path selection and data forwarding
• Wan access 、 Address translation and specific security functions