OSI reference model and hierarchical thinking
Network transmission process is a very complex process, it should first establish hierarchical thinking. Hierarchical model is designed to develop a method for the network protocol. Thought stratified essentially communication between nodes is to this complex problem into several relatively simple problem to solve each problem individually corresponding to one layer. Each layer to achieve a certain function, collaborate to achieve data communication this complex task.
When we use the network transmission, only to see both the sender and receiver, and the middle of the process from the sender to the recipient is not very understanding. 
The above-described image is a hierarchical representation of the OSI reference model, network traffic is divided into seven layers, each layer has its own functional role, the data transmission is completed cooperate with each other. I tell you about the role and function of each layer.
(1) Physical layer : create, maintain, is physically disconnected
from a computer, the cable is equivalent to the physical layer, network cards, fiber.
(2) Data Link Layer : establishing a logical connection, hardware address addressing, error checking and other functions
which is a packaging image data, the process of packing, confirmation is sent to the correct address data.
(3) Network layer : addressing logical address, to achieve different paths between network selection
This selection process is a network transmission path to ensure prompt and effective data transmission
(4) Transport Layer : definition of transmission of data protocol port number, flow control and error checking and
determining a data transmission from one port to another, to ensure the accuracy of the position data transmission
(5) session layer : creating, managing, suspended answer
to establish a session connection between the port and the port
( 6) Presentation layer: Representing data, security, compression
which is a data translation, encryption, compression process
(7) Application Layer : an interface to network services and end-user
can be understood as all APP we are now used
The application layer, presentation layer, session layer belonging to a layer of software; transport layer, network layer, data link layer, a physical layer belonging to the network level. Such interpretation is not easy to understand, with a life have occurred in our midst as an example to explain it, it is well understood every day.
Transmission of data like logistics and express parcels transport, so we can use the example to understand courier transmission of data!
Express parcel logistics is based on some basic factors easily accessible by road, passenger cars and other cargo, these factors are the physical layer. When we order a commodity, courier companies handling of our product is packed and labeled unique express orders, make sure you can safely express sent to your hands, which is the data link layer. After completion of the express package delivery trucks, and delivery of the first thing is to choose an optimal route, which is the role of the network layer. When the path selection is complete, the delivery truck and your city will be the site of the courier to contact you when the parcel will reach the site closest to you site, from the courier company to courier companies established in the times around you, is a a connection port, an instant transport layer port. Contact is the session layer courier truck to the site established to support. When the courier to the site, you receive a text message courier pick up, if it is to find your own package by wrapping the two-dimensional code and bar code words too time-consuming, so we need to give each parcel number, so that you can understand the meaning of a that shows the effect layer. So it is safe to express your hands up! Such a process would express our network and process data transmission, as you read this example should be able to understand the process of data transmission.
Therefore, the data transmission is a very complex process, we take hierarchical thinking, to simplify the process, a better understanding of their meaning.