The original purpose of the OSI seven-layer model is to define the basic architecture of the network interconnection, but the actual use of the structure does not completely follow it, for the computer network has been more mature today, he is only a computer network learners to learn the network of a model and the actual work of the reference model for a kind of troubleshooting. For the principle of one or two words can not say.

The function of each layer is such that, from top to bottom:

The seventh layer: the application layer data user interface, providing user program "interface".

Layer 6: Representation Layer Data The representation of data, the realization of specific functions, such as data encryption.

Layer 5: Session Layer Data Allows the establishment of sessions between users on different machines, such as WINDOWS

Layer 4: Transport Layer Segment Realizes data communication between user processes on different hosts in the network, reliable

and unreliable transmission, error detection in the transport layer, traffic control, etc.

Layer 3: Network Layer Packet Provides the logical address (IP), routing, and transmission of data from source to destination

.

Layer 2: Data Link Layer Frame Encapsulates upper layer data into frames, accesses medium with MAC address, error detection

and correction.

Layer 1: Physical Layer Bitstream Bitstream transmission between devices, physical interfaces, electrical characteristics, and so on.

Then I found a simple picture of the transmission to help you understand.

Each layer in detail that can be more, what do not understand you can ask, hope to adopt.