7 Layers of OSI Model In Easy Words

Home 7 Layers of OSI Model In Easy Words

OSI (Open System Interconnection) model defines a networking framework for implementation of protocols in seven layers of the OSI model. It is a reference model which describes the transmission of data over the network. It is a conceptual framework for understanding the relationship between every layer of the model. The main purpose of creating this model is to analyze the flow of data over the network (Zimmermann, 1980). OSI model is designated ISO/EEC 7498-1 and it is standardized by ISO (International Organization for Standardization). It is the general-purpose model which describes the flow of data in a layered architecture. OSI model has seven layered architecture for data transmission and each layer has its own operation.

Seven Layer of OSI Models

In this model, data is transmitted from one layer to another layer starting from the application layer that is Layer 7 and proceeding to the bottom layer over the channel to the next station and backs up the hierarchy (Day & Zimmermann, 1983). The OSI model takes the task of Inter-networking and divides the network into 7 different layers which are discussed below.

Layer 7

Application Layer

Layer 6

Presentation Layer

Layer 5

Session Layer

Layer 4

Transport layer

Layer 3

Network Layer

Layer 2

Data Link Layer

Layer 1

Physical Layer

  • Application Layer (7)

It is the last layer of the OSI model which supports application and end-user processes. Communication partners are identified and QoS is analyzed, the privacy of the user and user authentication is identified and moreover, constraints on data syntax are identified. All the things in this layer are application specific and this layer supports various application services such as e-mail, file transfer, network software services etc. For example NFS, SNMP, Telnet, HTTP, FTP.

  • Presentation Layer (6)

This layer is part of the OS (Operating system) and converts incoming and outgoing data from one presentation format to another such as clear text to encrypted text at one end and then reverse to clear text at other (Hollis, 1983). This layer includes ASCII, EBCDIC, TIFF, GIF, JPEG etc.

  • Session Layer (5)

The main function of this layer is to set up the session between the host machine web browser with the web server. The services provided in this layer include reconnection, authentication and on the internet TCP, a UDP protocol provides most of the applications. A layer of Session layer includes NFS, NetBios, SQL etc.

  • Transport Layer (4)

This layer is responsible for the packetization of data and then the delivery of the packets which includes the error checks in the data when it arrives at the layer (Knightson, 1983). It provides end-to-end recovery mechanism and flows control and it ensures the successful data transfer of data. This layer includes SPX, TCP, UDP etc.

  • Network Layer (3)

The main purpose of this layer is to handle addressing and routing of the data to its actual destination node. This layer uses switching and routing technologies and logical paths known as virtual circuits for transmitting data from one node to another node. Forwarding and Routing are functions of this layer along with internetworking, addressing, congestion control, error handling, packet sequencing are also part of this layer. This layer includes AppleTalk DDP, IP, IPX.

  • Data Link Layer (2)

This layer setup various links across the physical network by putting network packets into frames. This layer two categories that are Logical link Control Layer and MAC (Media Access Control). Media Access control types include Ethernet and 802.11 wireless specifications. This layer includes FDDI, PPP, ATM, IEEE 802.5/802.2, HDLC, Frame Relay etc.

  • Physical Layer (1)

It is the first layer of OSI model in which data is in the form of the bit. It provides the hardware for receiving and sending of data on a carrier which includes defining cards, cables and physical aspects such as RS232, Fats Ethernet and ATM protocol with physical layer components. This layer includes RJ45, FDDI, B8ZS etc.

References

Day, J., & Zimmermann, H. (1983). The OSI reference model. Proceedings Of The IEEE71(12), 1334-1340. Retrieved from https://ieeexplore.ieee.org/document/1457043

Hollis, L. (1983). OSI presentation layer activities. Proceedings Of The IEEE71(12), 1401-1403. Retrieved from https://ieeexplore.ieee.org/document/1457054

Zimmermann, H. (1980). OSI Reference Model--The ISO Model of Architecture for Open Systems Interconnection. IEEE Transactions On Communications28(4), 425-432. Retrieved from https://ieeexplore.ieee.org/document/1094702

Knightson, K. (1983). The transport layer standardization. Proceedings Of The IEEE71(12), 1394-1396. Retrieved from https://ieeexplore.ieee.org/document/1457052

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