Shulou(Shulou.com)06/02 Report--

OSI model

[1] Physical layer: establish, maintain, disconnect physical connections. * (Network card, network cable, hub, repeater, modem)

Hub: A physical layer device that transmits information in the form of broadcasts.

Main functions:

1---Provides tools for establishing, maintaining, and disconnecting physical connections. (Physical connections: network cables and the like)|）

2---Provide data stream transmission means on physical media to achieve synchronization between nodes.

[2] Data link layer: establish logical connection, perform hardware address addressing, error checking and other functions (bridge, switch)

1---It is used to establish, maintain and dismantle links to achieve error-free transmission.

2---Ensure message reliability on point-to-point or point-to-multipoint links.

3--Error control of adjacent channels, data framing, synchronization, etc.

Switch: A machine used to exchange messages, mostly link layer equipment (switch), capable of address learning, and exchanging messages in the form of store-and-forward.

[3] Network layer: logical address addressing to achieve path selection between different networks. (router)

1---By using the function provided by data link layer, the connection between two networks is realized through routing.

2--Provides protocols for establishing, maintaining and dismantling network connections.

Router: One of its roles is to connect different networks, and the other role is to select the route of information transmission. And choose the quickest shortcut, can greatly improve the communication speed, reduce the network system communication load, save network system resources, improve the network system smooth.

Transport layer: defines the protocol port number for transmitting data, as well as retention control and error checking.

1---Acknowledge the acceptance and forwarding of data frames between systems. end-to-end transmission control.

2--It is used to compensate for the quality difference of various passes, and there is still a difference in transmission after passing through the lower three layers, and the reliability of data frame transmission is further improved.

* Note (accept the data of the previous layer, divide the data when necessary, and hand over the data to the network layer to ensure that these data segments reach the opposite end effectively.

Session layer: Create and manage sessions between users on different machines.

Main task: Provide the presentation layer of two entities with the means to establish and use connections. A connection between different entities at the presentation level is called a session. The session layer's task is therefore to organize and coordinate communication between two session processes and to manage data exchange.

Users can establish sessions in half-duplex, simplex, and full-duplex modes. When establishing a session, users must provide the remote address they want to connect to.

Session Management: Allows users to establish, maintain, and terminate sessions between two physical devices and supports data exchange between them. For example, provide one-way sessions or two-way simultaneous sessions, and manage the order of transmission in the session, as well as the length of time the session takes.

Session flow control: Provides session flow control and cross-session functions.

3 Addressing: Use remote addresses to establish session connections.

Error control: Logically speaking, the session layer is mainly responsible for the establishment, maintenance and termination of data exchange, but the actual work is to receive data from the transport layer and correct errors. Session control and remote procedure calls belong to this layer of functionality. Note, however, that errors checked at this level are not errors of communication media, but rather high-level errors of disk space, printer out of paper, and so on.

[6] Presentation layer: syntax, semantics of information and their relationships, such as encryption and decryption, transformation and translation, compression and decompression. ----------- (Interprets commands and data from the application layer, assigns corresponding meanings to various syntaxes, and transmits them to the session layer according to certain formats.) Its main function is to "handle the representation of user information, such as encoding, data format conversion and encryption and decryption")

Application layer: various application protocols, HTTP, SMTP, FTP, POP3. The highest layer of the OSI reference model, which is the interface between computer users and various applications and networks. Its function is to provide services directly to users and perform various tasks that users want to do on the network. It is responsible for completing the connection between the application program and the network operating system in the network, establishing and terminating the connection between the users, and completing various protocols such as supervision, management and service required by various network services and applications proposed by network users. In addition, this layer is responsible for coordinating work between applications.

conclusion

In the seven-layer model, each layer provides a particular network function. From the point of view of network function: the following four layers (physical layer, data link layer, network layer and transport layer) mainly provide data transmission and exchange functions, that is, the communication between nodes is the main; the fourth layer, as a bridge between the upper and lower parts, is the most critical part of the entire network architecture; and the upper three layers (session layer, presentation layer and application layer) mainly provide information and data processing functions between users and applications. In short, the lower 4 layers mainly complete the function of communication subnet, and the upper 3 layers mainly complete the function of resource subnet.

Here is the TCP/IP layered model

┌────------────┐┌─┬─┬─-┬─┬─-┬─┬─-┬─┬─-┬─┬─-┐

│ ││D│F│W│F│H│G│T│I│S│U│ │

│ <$$> N <$I <$H <$T <$T <$O <$E <$R <$M <$S <$its <$

│第四层，应用层 ││S│N│O│P│T│P│L│C│T│E│ │

│ ││ │G│I│ │P│H│N│ │P│N│ │

│ <$<$$>$>$>$> E <$S <$$>$> E <$<$E <$<$E <$It <$

│ ││ │R│ │ │ │R│T│ │ │T│ │

└───────------─┘└─┴─┴─-┴─┴─-┴─┴─-┴─┴─-┴─┴-─┘

┌───────-----─┐┌─────────-------┬──--------─────────┐

│第三层，传输层 ││ TCP │ UDP │

└───────-----─┘└────────-------─┴──────────--------─┘

┌───────-----─┐┌───----──┬───---─┬────────-------──┐

│ ││ │ICMP│ │

│第二层，网间层 ││ └──---──┘ │

│ ││ IP │

└────────-----┘└────────────────────-------------─-┘

┌────────-----┐┌─────────-------┬──────--------─────┐

Layer 1, Network Interface <$ARP/RARP <$ other │

TCP/IP is organized into four conceptual layers, three of which correspond to the corresponding layers in the ISO reference model. ICP/IP protocol family does not contain physical layer and data link layer, so it can not complete the function of the whole computer network system independently, and must work with many other protocols.

The TCP/IP layered model has four protocol layers that perform the following functions:

Layer 1: Network Interface Layer

include protocol for cooperative IP data transmission over exist network media. The TCP/IP standard does not actually define functions corresponding to the ISO data link layer and physical layer, but provides an interface between the TCP/IP protocol data structure and actual physical hardware.

Layer 2: Internet Layer

The network layer corresponding to the OSI seven-layer reference model. This layer contains IP protocol, RIP protocol, routing information protocol), responsible for data packaging, addressing and routing. It also includes an Internetwork Control Message Protocol, which provides network diagnostic information.

Layer 3: Transport Layer

Corresponds to the transport layer of the OSI seven-layer reference model and provides two end-to-end communication services. TCP protocol provides reliable data stream transport service, UDP protocol provides unreliable user datagram service.

Layer 4: Application Layer

Corresponds to the application and presentation layers of the OSI seven-layer reference model. Internet application layer protocols include FTP(File Transfer Protocol), Gopher, HTTP(Text Transfer Protocol), Telent(Remote Terminal Protocol), SMTP(Simple Mail Transfer Protocol), IRC(Internet Relay Session), NNTP (Network News Transfer Protocol)!

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