OSI(Open Systems Interconnection model)

What is OSI Models?

OSI[Open System Interconnection] models is a set of rules that tells how different computer system can connect/communicate over a network. International Organisation developed OSI Model for standardisation.OSI Model is consists of 7 layers and each layer has a specific duties and responsibilities to perform and this approach help different technologies and devices to work together flawlessly. OSI Models helps to get a clear vision for managing networks and data transmission issues. The OSI Models facilitates structure data transmission by enabling interaction between adjacent layers and this process helps networks professionals troubleshoot issues easily and can focus on the specific layers where the issue exits.

What are the 7 layers of OSI Models?

The 7 layers of OSI Models are:-

• Application Layer.

• Presentation Layer.

• Session Layer.

• Transport Layer.

• Network Layer.

• Data Link Layer.

• Physical Layer.

  

  Explanation of each Layers of OSI Models.

• Application Layer (Layer 7) :- The topmost layer of OSI Model is Application layer. This layer provides an interface for users and applications to access network services. Application Layers enables data manipulation and it also ensures ease of access for different types of user. This layer directly communicates with the applications and offers common web service like HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), DNS (Domain Name System), to facilitate seamless connections.

  

• Presentation Layer (Layer 6) :- The 6th layer in the Open System Interconnection (OSI) Model is the Presentation layer is also known as Translation Layer. The sole responsibilities of this layer to translate the data for the network. The data which this Layer receives from the Application Layer is extracted and manipulated here as per the required format to transmit over the network. Main duty of Presentation Layer is to provide or define the data format and encryption.

• Session Layer (Layer 5) :- The 5th Layer in the Open System Interconnection (OSI) Model is the Session Layer. The duty of the Session Layer is to control and maintain connections between systems to share data. Session Layer set up, ends and maintains sessions across all channels. In case of networks error, it checks the authenticity and provides recovery options for the active sessions. Session Layer offers many networks protocols for safety, security and efficiency of communication between devices. Some of Protocols are RTCP (Real-time Transport Control Protocol), PPTP (Point-toPoint Tunnelling Protocol), PAP (Password Authentication Protocol), RPC (Remote Procedure Call Protocol).

• Transport Layer :- OSI (Open System Interconnection) Model has 7 layers and the Transport Layer sits at number 4 in the middle of the Layers and it plays an important role among all these Layers, it acts as a bridge between the Application Layers (top 3 Layers) and the Network Layers (bottom 3 Layers), and it ensures that the data generated by the Applications is effectively transmitted across the networks. Transport Layer also ensures that it prevents data overflow by managing the rate of data transmission based on the receiver’s capacity. Common Protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are operate at the Transport Layer. Transport Layer is also known as heart of OSI (Open System Interconnection) because the heart pumps blood to sustain the entire body, the Transport Layer ensures that data flows efficiently and reliably, supporting all other layers in the OSI (Open System Interconnection) Model. Without the transport layer, data communication would be chaotic and unreliable, much like a body without a functional heart.

• Network Layer :- The 5th Layer of OSI (Open System Interconnection) Model is the Network Layer and it plays a key role in data transmission. The responsibility of this layer is to maintain the quality of the data and pass and transmit from its source to its destination. Network Layer also handles the routing mechanism, which means that it chooses the best path to transmit the data from the source to its destination, not just transmitting the packets. The most important functions of Network Layers are :- Assigning Logical Address, Routing, Forwarding, Path Determination, Logical Subnetting, Fragmentation and Reassembly, Network Address Translator (NAT), Quality of Service (QoS), Error Handling, Interconnectivity, Encapsulation and Decapsulation, Congestion Control.

• Data Link Layer :- The 6th Layer in the OSI (Open System Interconnection) Model is the Data Link Layer and DDL ( Data Link Layer) is responsible for node-to-node delivery of data. DDL ( Data Link Layer) is also responsible for encoding, decoding, and organising the incoming and the outgoing data. DDL ( Data Link Layer) is considered as the most complex layer in OSI (Open System Interconnection) Model because it hides all complexities of the hardware from the other above layers. DDL ( Data Link Layer) is further divided into two parts:- i) Logical Link Control (LLC) and Media Access Control (MAC). DDL ( Data Link Layer) receives information from the Network Layer in form of Packets and it divides these Packets into small Frames and sends each Frames bit-by-bit to the Physical Layer. Protocols in Data Link Layers are Synchronous Data Link Protocol (SDLC), High-Level Data Link Protocol (HDLC), Serial Line Interface Protocol (SLIP) for encoding, Point to Point Protocol (PPP), Link Access Procedure (LAP).

• Physical Layer:- The 7th layer and the last layer of the OSI (Open System Interconnection) Model is the Physical Layer represents the electrical and physical characteristics of the network and its forms the foundation layer of network communication. It includes components like power plugs, connectors, receivers, and cables. This layer is responsible for transmitting raw data bits between devices and defines encoding methods (how 0s and 1s are represented in signals). Physical Layer maintains the data rate and also performs the Synchronisation of bits and also helps in Physical Topology (Mesh, Star, Bus,Ring) decisions (Topology through which we can connect the different devices with each other). Physical Layer Protocols are Ethernet with 1000BASE-T, Ethernet with 1000BASE-SX, Ethernet at 1000BaseT, Synchronous Digital Hierarchy/ Optical Synchronisation, Bluetooth, Networking for controllers, U.S.Serial Bus.

  

Protocols Used in the OSI (Open System Interconnection) Model Layers describe in the Image below:-

Conclusion

In Conclusion, OSI (Open System Interconnection) Model helps us to understand and get clarity that how data moves in the networks. OSI (Open System Interconnection) Model is consists of 7 layers: Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer and Application Layer. Each Layers has a certain role and responsibilities to perform. OSI (Open System Interconnection) Model is widely used to understand and troubleshoot the network issues.