Night comes wind and rain, "network" Know?

By learning "graphic TCP / IP" on the network have a certain understanding, write on this blog sort of network knowledge, imperfect welcome support.
1, appears in the background of computer networks

1, appears in the background of computer networks

1.1, from the independent mode to the network interconnection pattern

LAN LAN: more the number of computers, switches and routers connected together via

a wide area network WAN: the distant and computers together

1.2, the role of the computer network

Computer network is like a person's nervous system. A man of all physical sensations are transmitted to the brain via nerves. Similarly, information from around the world also passed to each person among computers over a network.

2, the development of computer network each stage seven

2.1 Batch

In order to let more people use computers, there has been a batch system. The so-called batch processing, first refers to the user program and data loaded cassette or tape, read by a computer in a certain order, the user is to be performed by way of these programs and data can be collectively batch processing.

2.2, time-sharing system

In the 1960s there has been time-sharing system. It refers to a plurality of terminals connected to the same computer, it allows multiple users to use a computer system.

2.3 Communication between computer

Communication technology between a computer (connected by a communication line between the computer and the computer). People can easily read and timely data to another computer station. Thereby greatly reducing the time of transmitting data.

2.4 generation, the computer network

The popularity of 2.5, Internet

Connecting heterogeneous computer network communication techniques, and generation of the World Wide Web.

2.6, Internet technology as the center of Times

Birth IP network.

2.7, establish a secure connection from a connection

As the transaction has two faces, convenience of the Internet has also brought negative issues to people's lives. Computer virus intrusion, information leaks, network fraud and other crimes using the Internet is increasing. Not simply concern connectivity, more attention to establish a secure connection.

3. Agreement

The importance of 3.1, the agreement

In simple terms, the agreement is a kind of through the network communication between the computer and the computer beforehand reached "agreement." This "agreement" between computers that enable the devices from different manufacturers, different CPU and different operating system components, as long as it is possible to follow the same protocol for communication. Conversely, if the agreement can not be achieved using different communication. This is like two people speak the language of different countries. How we can not understand each other.

Examples 3.2 protocols

4, protocol layering the OSI model

4.1 protocol layering

On the surface A with C is in direct dialogue with the Chinese, but in fact A and C are in by phone
to hear the voice sounds simple, speak into the microphone at all. Imagine if you have not seen a prime telephone people
see this scene is probably going to think he -? A and C would think given the telephone chat with it.
In fact, in this figure, the language they use the protocol as an audio input microphone communication device
layer is converted to a radio signal sent out. After transfer to the other side of the telephone, the communication device is converted back layer
as an audio output, passed to the other side. Thus, A and C is actually between the use of the telephone by converting audio
to achieve a dialog interface sound.

4.2, OSI Reference Model

The actual communication protocol packet can be quite complex. OSI reference model such a complex agreement collated and divided into seven hierarchical easy to understand.

1, the application layer
provides applications and services associated with a predetermined application details of the communication. Including file transfer, e-mail, remote login (virtual terminal) and other agreements.
2, the presentation layer
converts the information into a format suitable for the application processing network transmission, or the data from the upper layer is converted into the format that can be processed. Therefore, it is responsible for converting data formats. Specifically, it is converted to device-specific data format is a standard network transmission format. May be different for different devices results in the same bit stream explained. Thus, keeping them - this layer is induced by a major role.
3, the session layer
is responsible for establishing and breaking communications connection (logical data flow path), and the divided data and the like related to the transmission data management.
4, the transport layer
acts as reliable transmission. Only be processed on both sides of communication nodes, without having to deal on the router.
5, the network layer
transmits the data to the target address. A plurality of destination address may be linked together through a router network - an address. So this - layer is responsible for addressing and routing.
6, the data link layer
is responsible for the physical level interconnect, communication transmission between nodes. For example communication between two nodes with an ethernet connection. The 0,1 sequence into meaningful data frame transmitted to (and received data frame is generated) on the end.
7, the physical layer
is responsible for the level 0 bit stream (sequence 0,1) of the voltage, the flash light exchange between off.

5, network transmission

5.1, there is a link for the type and connectionless oriented

5.2, circuit switching and packet switching

Circuit switched
in circuit switching, the switch is mainly responsible for the data transfer process. The computer is connected to the first switch and between the switch and the number of switches by connecting a communication line to continue. Thus when transmitting data between computers, the need to establish a communication circuit through the switch and the destination host. We connect the circuit is called to establish a connection. After the connection is established, the user can always use this circuit until the connection is broken so far.

Packet switched
so that the computer is connected to the communication circuit data to be transmitted into a plurality of data packets, according to - the transmission after a predetermined order, respectively. This is packet switching.

5.3 classified according to the number of the receiving terminal

6. Address

Communication transmission, the transmitter and receiver may be considered as the main communication. They can be identified by the information out of a so-called "address". When people use the phone, the phone number is equivalent to "address." When people choose to write, mailing address, plus the name is equivalent to "address."
6.1, the uniqueness of the address
if you want to play a role in communication among address, you first need to determine the subject of communication. An address must be clear that a main object. At the same - communication networks are not allowed in the same two body communication address exists. This is the uniqueness of the address.

Level of 6.2, the address

In the case where the total number of addresses is not a lot, with the unique address can locate the body communicate with each other. An important question. For this reason it was discovered that in addition to address unique needs are hierarchical. In fact, in the process of using the telephone and mail communication, already have a hierarchical address this concept. For example, the phone number including the country code and the national area code, mailing address include the country name, province name, city name and region names. It was with this level of classification in order to locate a particular address more quickly.
MAC address and IP address when a communication identifying unique body although all, but only the IP addresses of them are hierarchical.
MAC addresses are designated by the device manufacturer for each card. People can manufacturer identification number, manufacturer part number and product inside a serial number to ensure uniqueness of the MAC address. However, it is unable to determine which card is which vendor uses which place.
Then the IP address is how to achieve a layered it? On the one hand, IP address consists of a network ID and a host ID. Different IP addresses even if the main communication if the number of different hosts, the same network number, indicating that they are on the same network segment. Typically, a network of host at the same department also belong to the same group or organization.