A, OSI reference model
1, OSI concepts
-Open System Interconnect 开放系统互连参考模型，是由ISO（国际标准化组织）定义的。它是个灵活的、稳健的和可互操作的模型，并不是协议，是用来了解和设计网络体系结构的。
2. The purpose of the OSI model
规范不同系统的互联标准，是两个不同的系统能够较容易的通信，而不需要改变底层的硬件或软件的逻辑。
3, OSI model is divided into seven
OSI把网络按照层次分为七层，由下到上分为物理层、数据链路层、网络层、传输层、会话层、表示层、应用层。
- User level
- Application layer: applications and interfaces
- Presentation Layer: data conversion, compression and encryption
- Session Layer: maintain data for different applications of partition
- The network level
- Transport Layer: provides reliable end to end error control packets and file transfer
- Network Layer: transmitting a packet from source to destination, the routing
- Data Link Layer: The packet data encapsulated in a frame, a node that provides a transmission error detection mode to the node
- The physical layer: the transmission bit on the media, to provide mechanical and electrical statute
4, the application layer
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Provides an interface for the application software is an application that can use the network services
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Application layer protocol created:
http(80)、https(443)、dns(53)、ftp(20/21)、smtp(25)、pop3(110)、telnet(23)
5, presentation layer
- Data decoding and encoding, encryption and decryption, compression and decompression
- Picture: jpg, gif. . .
- Audio: mp3, wma, aac. . .
- Video: MP4, avi
6, the session layer
- Responsible for establishing, managing and terminating indicates that the session layer connection between the layers
- Between a device or node providing session control, coordinate communication process, and provides three different ways to organize the communication between them
- Simplex Half duplex Full duplex
7, the transport layer (TCP / UDP)
- Responsible for establishing the connection from end to end, to ensure that messages between connected end to end
- Service point addressing, segmentation and reassembly, connection control, flow control, error control.
- Providing an interface (port) the application layer
8, the network layer (IP)
- Providing the logical address to the network device
- Routing, routing table maintenance
- It is responsible for the packet data transmission from source to destination
- Representative: Router
9, a data link layer (MAC)
- On an unreliable physical link, provide reliable data transmission services, the frame-hop (node) from moving to another hop (node).
- Framing, the physical addressing, flow control, error control, access control
- Representative: Switch
10, a physical layer
- By one bit from the responsible hop (node) to another hop (node).
- Define the interface and the physical characteristics of the media (line sequence, voltage, current)
- Definition of bits, said data transfer rate transmission mode, the signal
- Defines physical network topology (mesh, star, ring, bus topology, etc.)
- Representative: Hubs
Two, OSI Reference Model Architecture
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Feature
1, OSI model each layer has its own set of features
2, between the layers independent and interdependent
3, the upper layer depends on the lower layer, the lower layer to the upper layer service
Third, the link between the layers
Fourth, the transmission data
1, the package
- Each layer regarded as the upper layer protocol data portion of the packet, plus protocol headers creak, form their own protocol packet.
2, transmission
4, the received data
- Decapsulation
