Internet protocol by function: osi seven tcp / ip five tcp / ip four
First, why should the network hierarchy?
网络 The network node is to be performed or data to be transmitted forward, packing or unpacking, the control information is loaded or removed, etc., respectively, by various hardware and software modules to complete to delamination.
分层的原因：Through the network hierarchy, each layer responsible for a specific job, and the data is transferred to the next layer. Networking and communications to this complex issue may become more simplistic.
说人话就是：: Network transmission is a complex process, functional division, which will help to maintain and easy to upgrade the agreement, reduce the complexity of network communications.
好处：Each layer interacts only in his outer layer, and then does not need to know na what to do next layer.
(Meaning fried rice is delicious, Master Li has done, do not know which chickens under)
坏处: minutes so plurality of layers each process, performance will decrease. From bottom to top, top to bottom again.
Second, the simple explanation
| Application layer | It is to solve business problems, such as: file transfer, e-mail, file services | FTP, SMTP, DNS, Tenlent, WWW / HTTP and its secure infrastructure TLS / SSL |
| Transport Layer | Help the network message is converted into an application layer message can be read to provide end to end services | TCP、UDP |
| Network layer | To route packets, IP protocol in a wide area network, a host can send packets to another one (Internet) Host | IP、ICMP |
| Presentation layer | Help the network message is converted into an application layer message that can be read | HTML、JPEG、MP3、AVI、SOCKET |
| Session Layer | Connection is established, the session closes | |
| data link layer | In the LAN, or use the net address switch, the amount of packets to a further host | ARP |
| Physical Layer | Switches, computer room |
The TCP transport layer, network layer and the data link layer, the IP layer and the Ethernet protocol server supporting a push message WebSocket
- Session establishment message transmission 2. 3. 4. Close Session heartbeat
