TCP/IP four layer model and OSI seven layer model

TCP/IP four layer model

TCP/IP is synonymous with a set of protocols, and it also includes many protocols that make up the TCP/IP protocol cluster. TCP/IP protocol cluster is divided into four layers, IP is located in the second layer of the Protocol cluster (corresponding to the third layer of OSI), TCP is located in the third layer of the Protocol cluster (corresponding to the fourth layer of OSI).

Application layer: Transport Layer Interconnect Network Layer network Interface Layer : the management of the actual network media, define how to use the actual network (such as Ethernet, Serial line, etc.) to transmit data.

OSI seven-layer model

The OSI (Open System interconnection Reference model,osi/rm) model divides the work of network communication into 7 tiers, from low to high, respectively, to the physical layer (physical layer), and the Data link layer Link layer), the network layers, the transport layer (Transport layer), the session layer, the presentation layer (Presentation layer), and the application tier (application layer )。 The first layer to the third layer is the lower three layers of the OSI reference Model, which is responsible for creating links to network communication connections; Layers fourth through seventh are four layers above the OSI Reference Model, specifically responsible for end-to-end data communication.

in the OSI Reference Model, the unit of information exchanged between the peer layer protocol is collectively known as the Protocol Data Unit (PDU,PROTOCOL).
Transport Layer-data segment (Segment)
Network Layer--packet (packet) (Packet)
Data Link layer--data frame (frame)
Physical Layer-bit (bit)

First layer: Physical layer (Physicallayer)Specifies the mechanical, electrical, functional, and process characteristics of the communication equipment used to establish, maintain and dismantle physical link connections.　　Typical specification representatives include: Eia/tia RS-232, Eia/tia RS-449, v.35, RJ-45, etc. The main equipment of the physical layer:Repeaters, hubs.　　

Second layer: Data link layer (datalinklayer)On the basis of providing the bit-stream service in the physical layer, the data link between adjacent nodes is established, and the data frame (frame) is transmitted without error on the channel through error control, and the action series on each circuit is carried out. The data link layer provides reliable transmission on unreliable physical media.　　The functions of this layer include: Physical address addressing, data framing, flow control, data error checking, re-sending, etc. The Data Link layer protocol includes: SDLC, HDLC, PPP, STP, Frame Relay, and so on. Data Link Layer Main equipment: two-layer switch, bridge　　

The third layer is the network layerThere may be many data links between the two computers that communicate in the computer network, or they may go through many communication subnets. The task of the network layer is to select the appropriate inter-network routing and switching nodes to ensure the timely transmission of data. IP is part of the 3rd tier problem, and there are routing protocols and address resolution protocols (ARP). Everything about routing is handled on the 3rd level. Address resolution and routing are important purposes of layer 3. Network layer can also realize congestion control, Internet interconnection and other functions.　Network layer protocol representatives include: IP, IPX, OSPF, and so on. Network layer main device: router

Layer Fourth is the transport layer that processes the information (Transport layer)The Data unit at Layer 4th is also known as a packet (packets). The data unit of TCP is called segment (segments) and the data unit of the UDP protocol is called "Datagram (datagrams)". This layer is responsible for getting all the information, so it must keep track of the fragmentation of data units, the packets arriving in order of chaos, and other risks that may occur during transmission. The 4th layer provides an end-to-end (end-user to end-user) transparent, reliable data transfer service for the upper layers. The so-called transparent transmission refers to the transmission layer in the communication process to shield the upper layers of the communication transmission system specific details.representatives of the Transport Layer protocol include:TCP, UDP, SPX, and so on.

The fifth layer is the session layer , which can also be called the meeting layer or the dialogue layer, in the conversation layer and above the high level, the data transmission unit is no longer named, collectively referred to as the message. The session layer does not participate in specific transports, it provides mechanisms for establishing and maintaining communication between applications, including access validation and session management. 　　If the server verifies that the user is logged in, it is done by the session layer. The primary criteria for the session layer are "DIS8236: Session service Definition" and "DIS8237: Session protocol specification."　　

The sixth layer is the presentation layer (Presentation layer) which mainly solves the problem of the syntax representation of user information. It transforms the data to be exchanged from the abstract syntax appropriate for a user into the transfer syntax appropriate for internal use within the OSI system. That is to provide a formatted representation and Transform data service. Data compression and decompression, encryption and decryption are the responsibility of the presentation layer. The display of the example format is supported by the Protocol at the presentation layer.　　

The Layer Seventh application layer (application layer) Application layer provides an interface for operating system or network applications to access network services. representatives of the application layer protocol include: Telnet, FTP, HTTP, SNMP, and so on.

TCP/IP four-tier model and OSI seven-tier model correspondence table

Description: The biggest difference between TCP/IP and OSI is that the OSI is a theoretical network communication model, while TCP/IP is the actual running network protocol.

TCP/IP four layer model and OSI seven layer model