What is an OSI Model?
The OSI model is a conceptual framework for how applications communicate over a network. OSI stands for Open Systems Interconnection. This is a seven layer model. OSI reference model was the first standard model for network communications. The OSI model is widely used as it helps visualize and communicate how networks operates and also it helps to isolate and troubleshoot network problems.
This reference model works by top-down approach, which means from application layer to physical layer. These layers are provided by a mixture of network card drivers, operating systems, applications, and some networking hardware that facilitate the transmission of signals over ethernet, fiber optics, wi-fi, or other wireless protocols.
Layers in OSI Reference Model
7. Application Layer
Application layer is the top layer of the OSI model. This is the user interaction layer which provides network services to the end users. These network services are protocols that work with data the client is using. All of those interactive applications provide a set of services that allows the application layer to supply data to and receive data from the presentation layer.
Protocols : HTTP, HTTP, DNS, FTP etc.
6. Presentation Layer
Presentation layer performs the uncomplicated task of syntax processing or converting data from one format to another and also handles translating the data from the top layer to network format and vice versa. After the presentation layer processes, the information is then passed to the session layer or application layer, depending on whether the data is transmitting or receiving.
Protocols: SSL, TLS, MPEG, ASCH etc.
5. Session Layer
The construction, direction and conclusion of connection between devices occur is managed by session layer. This layer is responsible for authentication and reconnection if a network interruption should occur. After the session is established, the data then passes to or from the transport layer.
Protocols: NetBIOS, SAP etc.
4. Transport Layer
Transport layer is responsible for transmission of data across network connections. Also this layer coordinates how much data to send, how fast, where it goes and these sorts of things. Some protocols may provide additional capabilities including error recovery, data flow and retransmission. Once its functions are completed, the data is then passed to or from the network layer.
Protocols: TCP, UDP etc.
3. Network Layer
Network layer handles the routing of data. After the data arrives at this layer, each frame of data is examined to conclude if the data has reached it ultimate target. This layer sends data to the correct destination on both outgoing and incoming transmissions. IP(Internet Protocol) is the commonly known network layer for the internet. Also this layer manages the mapping between logical addresses and physical addresses. The data is then passed to the next required layer which is data link layer.
Protocols: IPV4, IPV6, ARP, IPSec, ICMP etc.
2. Data Link Layer
This is the most complex layer in the OSI model. Data link layer is divided into two sub layer and they are MAC (Media Access Control) and LLC (Logical Link Control). This layer sets up link across the physical network. When this layer receives data from physical layer, it checks for transmission errors and then packages the bits into data frames. From there, this layer manages the physical addressing methods for the MAC or LLC layers. Then the data is passed to or from the final layer which is Physical Layer.
Protocols: PPP, LCP, LAP etc.
1. Physical Layer
This is the electrical/physical layer. Physical layer consists of network cables, power plugs, cable pinouts, wireless radio frequencies, connectors, transceivers, receivers, repeaters etc. The troubleshooting of network problems starts from here. This layer transmits digital data bits from the source or sending device’s physical layer, over network communication media which can be electrical, mechanical or radio to the receiving destination device’s physical layer.
Protocols: RS232, ISDN etc.
