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This article introduces what is the basis of computernetwork, the content is very detailed, interested friends can use for reference, I hope it can be helpful to you.

1. Protocol 1.1 what is a network protocol

1. To put it simply, a network protocol is equivalent to an "agreement" specified between any two computers, which specifies the data format sent during network communication and the way to package and unpack data packets. As long as they abide by the implementation of the protocol, the two computers can achieve network communication, even if the two computers have different systems, different CPU and even different network hardware devices.

In ancient times, when passing confidential documents, there was a way of communication similar to protocols:

(1) place a bookshelf in An and B, and ensure that the books, book contents and books placed on the bookshelf must be placed in exactly the same order. (specify protocol)

(2) then A sends a letter, the original text of the letter should be encrypted according to the content on the shelf, and the text should be selected from the books on the shelf. The processed content of the letter is only the position of the book and the page number and row position of the text, which is completely incomprehensible to people. (package and send data according to the protocol)

(3) when the letter is sent to place B, the recorded information on the letter can be translated through the bookshelf in place B in the same way as in place A, and the understandable original text can be obtained. (unencapsulated packets are restored according to the protocol)

two。 Packet switching protocol: packet switching protocol refers to the need to transmit a large data as a whole, divided into small units of data packets, and then transmit these packets in turn.

Each packet in each packet has a header, which holds the address of the source host that sent the data and the address of the destination host that received the data.

3. Communication protocols usually specify which data information should be written in the header of the message, and how to deal with the information, that is, it specifies how the source host that sends the data constructs the header and how the receiving host handles the header of the parsing message. both parties must ensure a consistent definition and interpretation of the header.

1.2 Protocol layering of the OSI reference network model

1. Protocol layering: in the OSI network model, computer network protocols are divided into seven layers according to the functions they are responsible for. In this model, each layer can accept the specific services provided by the lower layer, and can provide specific services for the upper layer. The convention followed when interacting between upper and lower layer services is called "interface", and the interaction agreement between the same layer is called "protocol".

two。 Why protocol layering: the concept of protocol layering is actually the same as the modular idea in software development. Seven-layer network protocols work together to achieve communication, but each layer is independent. In other words, changes in one layer will not cause changes in other layers, only to ensure that the change layer protocol is consistent with the interface between the upper and lower layers, and layering defines the specific responsibilities and functions of each layer in detail.

3. The function (function) of each layer in OSI network model:

(1) layer 7-Application layer: provides services for the application and specifies the relevant details in the application, such as file transfer protocol, e-mail protocol, etc.

(2) layer 6-presentation layer: converts the data in the application program into a data format suitable for network transmission, that is, the data format transmitted in the lower layer, or converts the data from the lower layer into a data format that can be processed by the upper layer, that is to say, this layer is mainly responsible for data format conversion. After the presentation layer receives the data sent by the application layer, it needs to convert the received data into a "standard data format common to the network", because different systems or applications may have different interpretations of the same byte stream. The simplest example is character coding, if the sender application sends utf-8-encoded Chinese characters. On the other hand, the receiving application uses coding ISO-8859-1 to process the received data, then it is bound to produce garbled codes. So the purpose of the presentation layer is to convert the data transmitted from the application layer into a "standard data format common to the network", so that the receiver can use the same "standard data format common to the network" to ensure the correct representation of the data in the application layer. After the conversion, the data is handed over to the session layer for processing.

(3) layer 5-session layer: communication management, which is responsible for determining how to establish and disconnect communication connections, as well as management related to data transmission such as data segmentation.

(4) layer 4-Transport layer: manage the data transmission between the two nodes, establish and disconnect, and be responsible for reliable transmission

(5) layer 3-Network layer: transmits data to a destination address, which is an address formed by multiple networks connected by a router. Therefore, this layer is mainly responsible for addressing and routing.

(6) layer 2-data link layer: responsible for the communication and transmission between the interconnected nodes on the physical layer. Divide the 0ax 1 sequence into meaningful data frames for transmission

(7) the first layer-the physical layer: responsible for converting the 0 stroke 1 bit current into the voltage level and the flashing of the light.

4. The communication process of the OSI reference model is briefly introduced: as shown below, the sender processes the transmitted data from the top to the bottom of the application layer. When it is sent to the receiver, it processes the transmitted data from the physical layer to the bottom and displays it at the application layer. (the actual sending process must be much more complicated.)

two。 Transmission mode classification 2.1 for connectionless and connectionless

1. Connection oriented: it means that there must be a connected communication line (such as the TCP protocol) between the transceiver and the sending host before sending data.

two。 Connectionless: it means that it is not required to establish a connection first, and the sender can send data at any time, regardless of whether the receiver receives the data or whether the receiver exists (such as UDP protocol).

2.2 Circuit switching and packet switching

1. Circuit switching: this technology is applied to the old telephone network, where two computers communicate through a circuit to establish a connection until they are disconnected. however, when a computer uses a circuit connection to send and receive data, it monopolizes the whole line for data transmission, and other computers can only wait for the computer to disconnect before they can establish a connection to send and receive data, that is to say, the concurrency is very poor. So packet switching technology came into being.

two。 Packet switching: packet switching protocol is used here, the data to be sent is divided into small packets and sent sequentially, and each packet is correctly routed to the target host through the information in the header of the message. this allows multiple users to send and receive data on the same line at the same time, as shown in the following figure.

3. Address

In Internet communication, each host must have a unique "address", which can be used to find any host in the network. In the TCP/IP protocol, a combination of MAC address, IP address, and port number is used as the address identification of the host.

3.1 the nature of the address

1. Uniqueness: in a communication network, two communication hosts with the same address are not allowed to exist.

two。 Hierarchy: address layering is actually equivalent to writing your own home address. Address layering is used for IP addresses in countries, provinces, urban areas, counties, and townships. The biggest advantage of address layering is that it can quickly locate hosts.

4. The hardware of the network

1. Communication medium and data link: a medium that links and transmits data between computers through cables or electromagnetic waves (wireless networks), thus forming a network system.

two。 Network card: any computer connected to the network must have a network card (network interface card, network adapter, NIC).

3. Repeater: the first layer of the OSI model-the physical layer, in which the optical or electrical signals transmitted by the cable are processed by the repeater and transmitted to another cable.

4. Bridge / layer 2 switch: the bridge is the second layer of the OSI model-the data link layer, which is used to connect devices between two networks. The bridge is processed according to the MAC physical address

5. Router / layer 3 switch: a device that connects two networks and forwards packet messages corresponding to layer 3, the network layer.

6. Layer 4-7 switch: corresponds from the transport layer to the application layer, which is used to process data from the transport layer to the application layer.

7. Gateway: a device responsible for converting and forwarding data from the transport layer to the application layer, the same as the layer 4-7 switch, which handles data above the transport layer

What is the basis of computernetwork to share here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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