- It is a reference model for the way, applications communicate over a network. A reference model is a conceptual framework for understanding relationships. The Open Systems Interconnection Model is a seven-layer architecture with each layer having specific functionality to perform. All these layers work collaboratively to transmit data from one place to another.
- The OSI(Open Systems Interconnection) is split into 7 layers which divides the task into smaller more manageable task groups.
- The lowest layer (physical layer) is closest to the physical network medium (eg. Wires) & is responsible for placing data on the medium.
- The physical & the data link layer are implemented in hardware & software.
- The upper layers(layers-4,5,6 and 7) are implemented only in software. The lower layers are liable for the transportation of the data.
- The seven layers of function are provided by a combination of applications, operating systems, network card device drivers and networking hardware that enable a system to transmit a signal over a network Ethernet or fiber optic cable or through Wi-Fi or other wireless protocols.
The seven Open Systems Interconnection layers are:
- Layer 1: The physical layer–This layer contains data in the form of bits. It’s liable for the movement of bits from one node to another. It defines the characteristics of the interface between the devices and the transmission media. It also controls bit synchronization. The physical layer covers a various form of devices and mediums, among them cabling, connectors, receivers, transceivers and repeaters.
- Layer 2: The data-link layer–This layer is liable for the movement of frames from one node to the next. This layer is also liable for flow control, error control, and access control. This layer has two sub-layers: the logical link control layer and the media access control layer (MAC).
- Layer 3: The network layer–This layer handles addressing and routing the data — sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level. It uses the physical (MAC) address of networks.
- Layer 4: The transport layer– This layer manages packetization of data, then the delivery of the packets, including checking for errors in the data once it arrives. It provides services to the application layer and takes services from the network layer. Two main transfer layer protocols are UDP and TCP.
- Layer 5: The session layer– This layer is liable for dialog control and synchronization. It permits the communicating systems to enter into a dialog. Synchronization allows systems to add checkpoints.
- Layer 6: The presentation layer– This layer is liable for translation, compression and encryption/decryption of data and this layer is usually part of an operating system (OS) and converts incoming and outgoing data from one presentation format to another.
- Layer 7: The application layer–Also referred to as the desktop layer; this layer is liable for providing services to the user. For example DNS, Email. It is the set of services an application should be able to make use of directly, although some applications may perform application-layer functions.
It is essential to understand which layers exist in this model???
One easy way to memorize the layers of the OSI model is: “Please Do Not Throw Shahi Paneer Away”-
P: Please (Layer-1) Physical Layer
D: Do (Layer-2) Data-Link Layer
N: Not (Layer-3) Network Layer
T: Throw (Layer-4) Transport Layer
S: Shahi (Layer-5) Session Layer
P: Paneer (Layer-6) Presentation Layer
A: Away (Layer-7) Application Layer
I hope this post helps you to understand the OSI Layers which helps you to understand the dataflow over the network.
Keep learning 🙂