OSI 7 Layers

kc@example.com (kc kim) — Sun, 31 Dec 2017 02:30:37 +0900

OSI Reference Model (OSI 7 Layer)

One term that cannot be left out when discussing standardization in networking is “Open Systems Interconnection” (OSI). OSI is a network model established by the International Organization for Standardization (ISO) in 1977 as part of developing an architecture for communication between heterogeneous computer systems. It shows through what paths and methods data is transmitted and received. By understanding it, you can see how devices such as routers, bridges, switches, and network cards handle data. For people working in networking, OSI can be considered a kind of bible. OSI is called a collection of protocols because each layer that makes up the OSI model plays the role of a protocol. The OSI model consists of seven layers in total.

The fourth layer, the transport layer, through the seventh layer, the application layer, are generally called the upper layers. They are more closely related to application software than to network equipment.

Physical Layer

Defines the physical connection between computers and networks from both mechanical aspects, such as cables and connectors, and electrical aspects, such as voltage and signal modulation. Defines the network topology. Defines the signaling methods used on network media.

Data Link Layer

Defines the protocols that allow computers to exchange messages.

Provides reliable information transmission between two devices through a physical connection.

Network Layer

Defines the path through which packets are transmitted (routing).

Controls the flow of packets sent to nodes on the network and defines how status messages are delivered to network nodes.

Transport Layer

Defines how to locate physical positions on the network, establish connections between nodes, authenticate them, and arrange packets.

It is responsible for collecting packets in the proper order, checking for errors, and sending packets to the session layer.

Session Layer

Provides a conceptual interface to the transport layer for applications.

Allows devices to be identified by name instead of by network address.

Maintains sessions, or connections, between two nodes on the network.

Presentation Layer

Defines how applications enter the network and how data is translated into the form in which it is transmitted and consumed on the network.

If compression and encryption are used, they are also handled by the presentation layer.

Application Layer

The interface used by network-enabled applications to access the network.

Defines network applications.

This is the layer where email and network utilities exist.

It controls application access to the network and notifies applications when network errors occur.

Reasons for Developing Layered Protocols

Layered protocols were developed to separate complex networks by role area so they can be understood logically and more easily. They also provide standardized interfaces between network functions, ensure symmetry among functions performed at each node in the network, and clarify the language used when network designers, administrators, vendors, and users discuss network functions.

OSI 7 Layers

Application Layer (Top Layer)

This layer defines services that support users and application tasks. It manages FTP, databases, remote access (TELNET), email, and similar services.

Presentation Layer

This layer formats data sent from the application layer above it into basic codes such as ASCII or EBCDIC.

Session Layer

This layer manages LAN users when they connect to a server, including connection setup, maintenance, and termination.

Transport Layer

This layer is related to protocols such as TCP and SPX, and is associated with data transmission, error recovery, flow control, and network addressing.

Network Layer

This layer contains the conditions needed to assign destination addresses to data and determine transmission paths. It is the area where various transport protocols such as IP and IPX operate. It manages system connection devices and packets.

Data Link Layer

This layer defines how data packets are formed and transmitted. For example, it plays the role of loading letters onto delivery trucks, sending each truck onto the highway, and ensuring that they arrive safely.

Physical Layer

This layer converts data packets formed by the upper data link layer into electrical or optical signals and transmits and receives them. It can be compared to the trucks and highways needed to deliver letters to different locations.

devkuma – OSI

OSI 7 Layers

OSI Reference Model (OSI 7 Layer)

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Session Layer

Presentation Layer

Application Layer

Reasons for Developing Layered Protocols

OSI 7 Layers

Application Layer (Top Layer)

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer