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Computer Study Notes on OSI Layers – Learn Dunia

The Open System Interconnection(OSI) model is a reference model developed by ISO(International Organization for Standardization) in 1984, it defines a networking framework to implement protocols in seven layers, which divides the task involved with moving information between networked computers into seven smaller, more manageable task groups.

Seven Layers of OSI Model can be divided into two groups: Upper Layer(Layer 5,6,7) and Lower Layer(Layer 1,2,3 and 4). The Upper Layer of OSI Model deals with Applications issues and generally are implemented only in software. The Lower Layer of the OSI Model handles data transport issues. The Physical Layer and Data Link Layer is Implemented in Hardware and Software.


Layer 1: Physical Layer

The Physical Layer is the Lowest Layer of the OSI Model, it is concerned with the transmission and reception of the unstructured raw bit stream over a physical medium, Physical Layer focuses on Hardware elements such as Cables, Repeaters and NIC(Network Interface Card). the Most Common Protocol Used in OSI Layer is Ethernet.

Networking Devices Used in Physical Layer: Hub, Repeaters, NIC, Cables, Gateway.

Protocol data Unit: Bit,   Protocol: Ethernet.

Layer 2: Data Link Layer

When Obtaining data from the Physical Layer, the Data Link Layer checks the physical transmission error and packages bits into data “frames”.The Data Link Provides error-free transfer of data frames from one node to another over the physical layer, The Data Link Layer also manager the Physical Address such as MAC address.

The Data Link Layer is Divided into two sub layers: Media Access Control Layer(MAC) and the Logical Link Control(LLC), The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Networking Devices used in Data Link Layer: Bridge, Gateway, Ethernet Switch, Proxy Server.

Protocols: Ethernet, Point to Point Protocol(PPP).

Layer 3: Network Layer

The Network Layer Handles the addressing and routing of data, when data is arrives to the Network Layer the source and the destination addresses contained inside each frame are examined to determine if the data has reached its final destination.

Networking Devices used in Network Layer: Router, Gateway, Proxy Server.

Protocols: ARP(Address Resolution Protocol),  IPV4/IPV6, RIP.

Layer 4: Transport Layer

The Transport Layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control, The transport layer controls the reliability of communications through flow control, segmentation, and error control. Two great examples of transport protocols are TCP (as in TCP/IP) and UDP.

Networking Device used in Transport Layer: Gateway, Proxy Server.

Protocols: TCP, UDP.

Layer 5: Session Layer

This layer sets up, coordinates and terminates conversations. Services include authentication and re connection after an interruption. On the Internet, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) provide these services for most applications.

Networking Devices used in Session Layer: Gateway, Logical Ports.

Protocols: RPC(Remote Procedure Call).

Layer 6: Presentation Layer

The Presentation layer is the simplest in function of any piece of the OSI model, this layer usually part of an Operating System(OS) and converts incoming and outgoing data from one format to another.

Networking Devices used in Presentation Layer: Gateway.

Protocols: MPEG(Moving Pictures Expert Group).

Layer 7: Application Layer

Application Layer is the last layer of the OSI Layer. The Application layer supplies network services to end-user applications, This layer provides application services for file transfers, e-mail, and other network software servicesTelnet and FTP are applications that exist entirely in the application level.

Networking Devices used in Application Layers: Gateway.

Protocols: DNS(Domain Name System), FTP(File Transfer Protocol), POP3( Post Office Protocol version 3), IMAP(Internet Message Access protocol), Telnet, HTTP( Hyper Text Transfer Protocol).

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