🌐 Model and Concept of OSI and TCP/IP

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OSI model concept and basic protocols

The OSI model (Open Systems Interconnection Basic Reference Model, 1978) is an abstract network model for communications and the development of network protocols. Represents a layered approach to networking. Each layer serves its own part of the interaction process. Thanks to this structure, the cooperation of network equipment and software becomes much simpler, more transparent and clearer.

Today, the main protocol stack in use is TCP/IP, the development of which was not related to the OSI model and, moreover, was carried out before its adoption. During the entire existence of the OSI model, it has not been implemented and, obviously, will never be implemented. Only a subset of the OSI model is in use today. It is believed that the model is too complex, and its implementation will take too much time.

Some experts also claim that the history of the OSI model is a typical example of a failed and disconnected project.

№	Layer	Data type	Function	Example
7	Application	Message	Access to network services	HTTP, FTP, SMTP, DNS, SSH
6	Presentation	Data	Representation and encryption of data	ASCII, JPEG, GIF, SSL, TLS
5	Session	Data	Network session management	NetBIOS, Sockets
4	Transport	Segment Datagram	Direct connection between points	TCP, UDP
3	Network	Packets	Routing and logical addressing	IPv4, IPv6, AppleTalk, Routers
2	Data link	Frames	Physical addressing (LLC, MAC)	IEEE, Ethernet, DSL, Switches
1	Physical	Bits	Signals, network environment	USB, twisted pair, optical cable, coax, hubs

Concepts and basic protocols of the TCP/IP stack

TCP/IP is a network model for transferring data presented in digital form. The model describes the method of data transmission from the information source to the recipient. The model assumes the passage of information through four levels, each of which is described by a rule (transmission protocol). Sets of rules that solve the problem of data transfer make up the stack of data transfer protocols on which the Internet is based.

The name TCP/IP comes from the two most important protocols of the family Transmission Control Protocol (TCP) and Internet Protocol (IP) The protocols were first developed and described in this standard.

№	Layer	Data type	Function	Example
4	Application	Message	Access to network services	HTTP, FTP, SMTP, DNS, SSH, Telnet
3	Transport	Segment Datagram	Direct connection between points	TCP, UDP
2	Network	Packets	Routing and logical addressing	IPv4, IPv6, IPSec, AppleTalk
1	Network interface	Frames	Signals, network environment	Ethernet, IEEE 802.11, USB, twisted pair, optical cable, coax, hubs