what is the OSI model ?

• OSI model stands for Open Systems Interconnection Model.
• This model focuses on providing a visual design of how each communications layer is built on top of the other
• The open systems interconnection (OSI) model is a conceptual model created by the International Organization for Standardization
• which enables diverse communication systems to communicate using standard protocols.
• OSI 7-layer model is still widely used, as it helps how networks operate, and helps isolate and troubleshoot networking problems.

Layers of OSI Model

There is total 7-layers in the OSI Model .

1. Application
2. Presentation
3. Session
4. Transport
5. Network
6. Data-Link
7. Physical

How we can graphically represent the OSI Model ?

Let's learn how each layers communicates with each other

Application Layer

• The Application layer enables the user to interact with the application or network whenever the user elects to read messages, transfer files or perform other network-related tasks.
• Only the users Interact with Application layer.
• Applications like browsers,Skype Messenger apps.

Presentation Layer

• Presentation Layer takes data from the application layer and converts it into the machine/binary Language.
• Presentation Layer also provides Abstraction.
• The Encryption takes place at presentation layer.
• Presentation layer Compares the data before it transfers the data to session layer.

Session Layer

• This layer is responsible for the establishment of connection, maintenance of sessions, authentication, and also ensures security.
• It enables sending and receiving data followed by termination of the connected session.
• The session layer allows two systems to start communication with each other in half-duplex or full-duplex.

Transport Layer

• The transport layer provides services to the application layer and takes services from the network layer.
• Transport layer controls the amount of data going to be transported.
• In Transport layer Error control takes place.
• At sender’s side: Transport layer receives the formatted data from the upper layers and performs Segmentation.

Transport Layer provides two types of services.

1. Connection-Oriented Service: In this type of transmission, the receiving device sends an acknowledgement, back to the source after a packet or group of packets is received. This type of transmission is reliable and secure.
2. Connection-less Service : In this type of transmission, the receiver does not acknowledge receipt of a packet. Connection-less Service allows for much faster communication between devices.

Network Layer

• The network layer works for the transmission of data from one host to the other located in different networks.
• it provides a logical address and makes an IP packet.
• It also takes care of packet routing and Load balancing.
• Segment in Network layer is referred to as Packet.

Data-Link Layer

• The data link layer is responsible for the node-to-node delivery of the message.
• The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer.
• Data-Link Layer assigns physical / MAC address to the data packet to frame.
• Packet in Data Link layer is referred to as Frame.

  Data-Link performs functions

  1. It allow all the upper layer OSI Model to access frame which are going to transferred by data-link layer.
  2. It Controls how the data is placed and received from the media's using MAC(Media Access Control).
  3. Data link layer provides the mechanism of error control in which it detects and re-transmits damaged or lost frames.

Physical Layer

• The lowest layer of the OSI reference model is the physical layer.
• Physical Layer contains the hard wares like Hub, Repeater, Modem, Cables and it transmits electrical signal.
• It is responsible for transmitting individual bits from one node to the another.