Foreword
OSI seven-layer model: a purely theoretical model, for all practical devices and protocols can not correspond to the theoretical model.
Each layer corresponds to the actual device
Physical Layer: repeaters, hubs, UTP
Data Link Layer: bridge, Ethernet switch, card
The network layer: routers, three switches
Transport Layer: four switches, routers four
(Supplement, four switches and three switches difference: switch has three switches is part of router functions, the most important objective is to accelerate the large-scale three switches within the LAN data exchange, routing can be done once, many times based forwarding. technical switch MAC address and IP address, can greatly improve the data transfer rate between nodes, but can not autonomously determine or limit the dynamic data exchange and traffic ports according to the application requirements of the host port. L4 switch only end exchange can be completed, but also according to the characteristics of the application port of the host, determining, or limit its switching traffic. is based on the exchange of transport layer packets, is based on a class of TCP / IP protocol the user needs to exchange application layer applications new LAN switch. support TCP / UDP protocol all below the fourth layer, may be identified at least 80 bytes of packet header length, the application can be distinguished according to the type of packet TCP / UDP port number, thereby achieving the application layer access control and quality assurance services. so, not so much the fourth layer switch is a hardware network Devices, than it is a software NMS.)
Data transmission process
pa-a transmission to a pc-b
Precautions
1, the three is to provide users with services, under the four responsible for the actual data transfer
2, the transport layer transmission unit (data packet segment), network layer (packet message packet), the data link layer (data frame), the physical layer (bit)
3, only the upper layer more, the current layer can be identified following transactions; the lower the fool, close hardware
4, the transmission data to a lower layer data transmission, data transmission is received from the upper layer from the lower layer to an upper layer
5, the data transfer can not cross the interface between each pass through the logic
6, the physical layer is responsible for the actual data transfer, but the other layers corresponding to Logic
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