TCP IP Protocol notes (1)--Introduction

Preface
I have a bad memory, reading forgetful, to this note to record after reading their own knowledge of the thought, has reached a deeper understanding of TCP IP, this note is only I read the book after the summary of their own, right when the book after review.

I. Why there is a TCP IP protocol
We know that there are 56 nationalities in China, each nation has its own language, the language has formed the barriers of all nationalities, everyone said their own language, who can not understand what each other is speaking, language is the gap between the different nationalities, who also cross, according to each nation is a small group, Nations cannot work together as a big group. Putonghua solved this problem, in the national gap between the establishment of a bridge, so that people can exchange between, to avoid unnecessary conflicts.
TCP IP protocol is also the case, computer systems, hardware, to make each computer interconnected, you have to share a set of computers with the same communication protocol, TCP IP has played this role, so that each computer interconnected, can communicate with each other, forming A large network "internet"

Two. TCP IP tiering
The TCP IP protocol is divided into four tiers and each layer is responsible for different communication functions.
Data Link layer: Refers to the network interface and drive
Network layer: Information in the network transmission, the processing of packets in the network transmission activities, such as IP protocol. The IP protocol is unreliable, it does not confirm that the message is successful, this step requires the upper TCP protocol to handle
Transport layer: Responsible for the transmission of the network, mainly divided into TCP and udp,udp is not reliable, it is only responsible for data transmission to the destination network equipment, will not confirm whether it is the destination network equipment successfully obtained, the confirmation of the message acceptance and other operations need to be processed by the application layer. TCP is secure , and it includes operations that confirm the successful transmission of acknowledgement messages such as receiving and sending, time-out retransmission, and so on.
Application tiers: Applications such as the HTTP protocol
In the Internet, we can divide the entire system into end systems and intermediate systems:
End system: Two hosts in the Internet are both end systems. The application layer and the transport layer are the end-to-end protocols applied to the end system, and only the end system is used to the application layer and the transport layer.
Intermediate system: the middle router. The network layer provides a hop-on protocol for the Intermediate system, and the end system and intermediate system are used to the network layer.
Three. Internet address
Each host has an IP address to identify it, and even a host can have multiple IPs. IP addresses can be divided into 5 categories:

Four. Domain Name System
Access to the Internet host, we can through the host's IP access, can also be accessed through the host domain name, IP and host domain name is the corresponding
Five. Encapsulation
Communication between the two hosts, the data is encapsulated in the protocol stack and then transferred to the destination host:
1. The application assembles the data format and then sends it to the kernel protocol stack. TCPIP layer Four is also only the application layer is executed in the process, the other three layers are in the kernel protocol stack
2. The protocol stack receives application layer data, adds TCP or UDP headers to it, and TCP, UDP headers have a 16-bit port number to represent the application-layer protocol.
3. Encapsulate the IP header, add the transmission information, the IP header with 8bit to indicate what the upper layer is the protocol
4. Encapsulate Ethernet header, add network pretext information, use 16bit to indicate what protocol the upper layer is
Six. Sub-use
When the host receives the message, it parses the message from the bottom up and then gives the application layer information to the user process.
Servers are generally divided into concurrent servers and duplicate servers:
Concurrent server: The server initiates a process to process when it receives a client request, ends the process when it finishes processing, and can respond to requests from multiple clients at the same time
Duplicate server: The server receives a client request to process it immediately, but during processing, requests from other clients are blocked and the next client can be responded to as long as the current processing is complete

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TCP IP Protocol notes (1)--Introduction