ISO/OSI model

The top seven models of ISO are Layer 1 to Layer 7:

Application Layer)
Presentation Layer)
Session Layer)
Transport Layer)
Network Layer)
Data Link Layer)
Physical Layer)

The upper layer is called the upper layer, which defines the communication and man-machine interface between applications. What does it mean? The upper layer is responsible for converting what the computer can understand into what you can understand, or converting what you can understand into what the computer can understand.
The lower layer is called the underlying layer, which defines how data is transmitted end-to-end, physical specifications, and data-to-photoelectric signal conversion.

The application layer is a simple application. This layer is responsible for determining communication objects and ensuring that sufficient resources are used for communication. These are of course what applications want to communicate.

The presentation layer is responsible for data encoding and conversion to ensure the normal operation of the application layer. This layer is the conversion between the interface and binary we see, that is, the conversion between our language and machine language. Data Compression, decompression, encryption, and decryption all occur at this layer. This layer processes data in different formats based on different application purposes, and shows the various file extensions we see.

The Session Layer is responsible for establishing, maintaining, and controlling sessions, distinguishing different sessions, and providing single-work (simplex) and half-duplex (half)
Duplex), full duplex (Full Duplex) communication mode services. What we know at ordinary times is that NFS, RPC, and windows all work on this layer.

The Transport Layer separates and combines data to implement end-to-end logical connections. Data is integral on the top three layers, and is split at this layer. The split data is called segments ). Three-way handshake, connection-oriented or non-connection-less-oriented services, and flow control occur at this layer.

Network Layer: Manages network addresses, locates devices, and determines routes. The well-known IP addresses and routers work on this layer. The upper-layer data segments are separated at this layer. encapsulation is called packet. There are two types of packages. One is data packets, which is the user data transmitted from the upper layer; the other type is route update packets, which is directly sent by the router and used to exchange route information with other routers.

The data link layer prepares physical transmission, CRC verification, Error Notification, network topology, and traffic control. The well-known MAC addresses and switches work on this layer. The package transmitted from the upper layer is separated and encapsulated and called frame ).

The physical layer is a physical link that sends and receives data in bits.

The TCP/IP protocol does not fully comply with the OSI Layer-7 Reference Model. The traditional Open System Interconnection Reference Model is a layer-7 abstract reference model of communication protocols, where each layer executes a specific task. This model aims to make various hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transmission layer, voice layer, presentation layer and application layer. The TCP/IP communication protocol uses a layer-4 hierarchy. Each layer calls the network provided by its next layer to meet its own needs. The four layers are:

Application Layer: layer for communications between applications, such as simple Email transmission (SMTP), file transfer protocol (FTP), and network remote access protocol (Telnet.

Transport Layer: In this layer, it provides data transmission services between nodes, such as transmission control protocol (TCP) and User Datagram Protocol (UDP, TCP and UDP add transmitted data to the data packet and transmit it to the next layer. This layer is responsible for transmitting data and confirming that the data has been delivered and received.

Interconnect Network Layer: provides basic data packet transmission functions so that each data packet can reach the target host (but does not check whether it is correctly received), such as Internet Protocol (IP ).

Network Interface Layer: manages the actual network media and defines how to transmit data using the actual network (such as Ethernet and serial line.

IP
Internet Protocol IP is the heart of TCP/IP and the most important protocol in the network layer.
The IP layer receives a packet from a lower layer (network interface layer, such as an Ethernet device driver) and sends the packet to a higher layer-TCP or UDP layer, the IP layer also sends packets received from the TCP or UDP layer to the lower layer. IP packets are unreliable because the IP does not do anything to confirm that the packets are sent in order or are not damaged. An IP packet contains the address (source address) of the host that sent the packet and the address (Destination Address) of the host that received the packet ). When receiving data packets, high-level TCP and UDP services generally assume that the source address in the packet is valid. It can also be said that IP addresses form the authentication basis for many services. These services believe that data packets are sent from a valid host. IP validation contains an option called IP source routing, which can be used to specify a direct path between the source address and the destination address. For some TCP and UDP services, the IP packet using this option seems to be transmitted from the last System in the path, rather than from its real location. This option exists for testing, indicating that it can be used to fool the system for a normally prohibited connection. Therefore, many services that rely on the IP Source Address for confirmation will have problems and will be illegally infiltrated.

TCP
If an IP packet contains a TCP packet that has been blocked, the IP will send them to the upper layer. TCP sorts packets and checks errors to connect virtual circuits. TCP packets include serial numbers and validation, so packets not received in order can be sorted, and damaged packets can be re-transmitted. TCP sends its information to higher-level applications, such as telnet service programs and customer programs. Applications send information back to the TCP layer in turn, and the TCP layer forwards them down to the IP layer, device drivers and physical media, and finally to the receiver. Connection-oriented services (such as telnet, FTP, rlogin, X Windows, and SMTP) require high reliability, so they use TCP. In some cases, DNS uses TCP (sending and receiving domain name databases), But UDP is used to transmit information about a single host.

What are the layer-7 TCP/IP protocol and ISO layer-7 model? The role of ISO is the transition layer of the application layer presentation layer (Session Layer) the network layer (Network Layer) data link layer (Physical Layer) is called a high-level layer, which defines communication and human-machine interfaces between applications. What does it mean? The upper layer is responsible for converting what the computer can understand into what you can understand, or converting what you can understand into what the computer can understand. The lower layer is called the underlying layer, which defines how data is transmitted end-to-end, physical specifications, and data-to-photoelectric signal conversion. The application layer is a simple application. This layer is responsible for determining communication objects and ensuring that sufficient resources are used for communication. These are of course what applications want to communicate. The presentation layer is responsible for data encoding and conversion to ensure the normal operation of the application layer. This layer is the conversion between the interface and binary we see, that is, the conversion between our language and machine language. Data Compression, decompression, encryption, and decryption all occur at this layer. This layer processes data in different formats based on different application purposes, and shows the various file extensions we see. The Session Layer is responsible for establishing, maintaining, and controlling sessions, distinguishing different sessions, and providing services in three communication modes: Single-work (simplex), half-duplex (Half Duplex), and full-duplex (Full Duplex. What we know at ordinary times is that NFS, RPC, and windows all work on this layer.
The answer complements the transport layer, which separates and combines data to achieve end-to-end logical connections. Data is integral on the top three layers, and is split at this layer. The split data is called segments ). Three-way handshake, connection-oriented or non-connection-less-oriented services, and flow control occur at this layer. Network Layer: Manages network addresses, locates devices, and determines routes. The well-known IP addresses and routers work on this layer. The upper-layer data segments are separated at this layer. encapsulation is called packet. There are two types of packages. One is data packets, which is the user data transmitted from the upper layer; the other type is route update packets, which is directly sent by the router and used to exchange route information with other routers.

Supplement

The data link layer prepares physical transmission, CRC verification, Error Notification, network topology, and traffic control. The well-known MAC addresses and switches work on this layer. The package transmitted from the upper layer is separated and encapsulated and called frame ). The physical layer is a physical link that sends and receives data in bits. The TCP/IP protocol does not fully comply with the OSI Layer-7 Reference Model. The traditional Open System Interconnection Reference Model is a layer-7 abstract reference model of communication protocols, where each layer executes a specific task. This model aims to make various hardware communicate with each other at the same level. These seven layers are: physical layer, data link layer, network layer, transmission layer, voice layer, presentation layer and application layer. The TCP/IP communication protocol uses a layer-4 hierarchy. Each layer calls the network provided by its next layer to meet its own needs. The four layers are: Application Layer: layer for inter-application communication, such as simple Email transmission (SMTP), file transfer protocol (FTP), and network remote access protocol (Telnet.
Supplementing the Internet Protocol IP address is the heart of TCP/IP and the most important protocol in the network layer. The IP layer receives a packet from a lower layer (network interface layer, such as an Ethernet device driver) and sends the packet to a higher layer-TCP or UDP layer, the IP layer also sends packets received from the TCP or UDP layer to the lower layer. IP packets are unreliable because the IP does not do anything to confirm that the packets are sent in order or are not damaged. An IP packet contains the address (source address) of the host that sent the packet and the address (Destination Address) of the host that received the packet ). When receiving data packets, high-level TCP and UDP services generally assume that the source address in the packet is valid. It can also be said that IP addresses form the authentication basis for many services. These services believe that data packets are sent from a valid host. IP validation contains an option called IP source routing, which can be used to specify a direct path between the source address and the destination address. For some TCP and UDP services, the IP packet using this option seems to be transmitted from the last System in the path, rather than from its real location. This option exists for testing, indicating that it can be used to fool the system for a normally prohibited connection. Therefore, many services that rely on the IP Source Address for confirmation will have problems and will be illegally infiltrated.

TCP/IP only has four layers (application layer, transport layer, Interconnection layer, host-Network Layer ).
The OSI model has seven layers (application layer, presentation layer, Session Layer, transmission layer, network layer, data link layer, and physical layer ).
OSI protocol later than TCP/IP protocol