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OSI seven-tier reference model diagram:

The seven-layer model, also known as the OSI (Open System Interconnection) reference model, is a standard system developed by the International Organization for Standardization (ISO) for the interconnection of computers or communication systems. It is a seven-layer, abstract model, including not only a series of abstract terms or concepts, but also specific protocols. Definition:

The OSI (Open System Interconnection) reference model is a standard system developed by the International Organization for Standardization (ISO) for the interconnection between computers or communication systems, which is generally called the OSI reference model or seven-layer model. Layering: application layer

An interface between a network service and an end user.

The protocols are: HTTP FTP TFTP SMTP SNMP DNS TELNET HTTPS POP3 DHCP

Physical devices: computer presentation layer

Data representation, security, compression. (it has been merged into the application layer in the five-tier model)

Format: JPEG, ASCll, DECOIC, encrypted format, etc. Session layer

Establish, manage, and terminate sessions. (it has been merged into the application layer in the five-tier model)

Corresponding host process, which refers to the ongoing session transport layer between the local host and the remote host

Define the protocol port number over which data is transmitted, as well as flow control and error checking.

The protocols are: TCP UDP, once the packet leaves the network card, it enters the network transport layer.

Data units: segment

Physical devices: firewall network layer

Logical address addressing is carried out to realize the path selection between different networks.

The protocols are: ICMP IGMP IP (IPV4 IPV6) ARP RARP

Data units: package

Physical devices: router data link layer

Establish logical connection, hardware address addressing, error check [2] and other functions. (protocol defined by the underlying network)

The bits are combined into bytes and then combined into frames, and the media is accessed with an MAC address. Errors are found but cannot be corrected.

Data units: Fram

Physical devices: switch physical layer

Establish, maintain, and disconnect physical connections. (protocol defined by the underlying network)

Data units: bits / bit stream

Physical equipment: network card, repeater

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