Open Systems Interconnection - OSI
OSI is a 7-layer Architecture. The OSI model was created to make network devices and network protocols interoperable. It allows components, such as hard drives and video cards, to function in a computer or network independent of the manufacturers. In networking, the OSI model defines how media, protocols, and standards work together. Each layer has specific functionality to perform.
1. Physical Layer:
It is the lowest layer in the OSI 7-layer model. It is the actual physical connection between devices. It is responsible for the transmission and reception of unstructured raw data between devices such as Network interface controllers, Ethernet Hub, and Network switches.
This layer only understands or processes raw data as 0's and 1's as shown below.
Encoding/Decoding:
This data will go through multiple stages for multiple conversions. So data must be recovered in the flow. If there is a data loss or mismatch then the total chip functionality will collapse. So encoding is required to protect the data.
To recover original data from errors or losses decoding mechanism is required.
Serialization or Deserialization:
Most of the networking protocol Data Link Layer will work with 8bit, 16bit, 32bit, and so on bus widths. So this data has to be serialized to perform Digital to Analog conversion of the data. So Serializer is used for parallel-to-serial conversion or serial-to-parallel conversion.
Deserialization for vice versa.
Digital to Analog or Analog to Digital conversion:
The physical layer will transfer data through physical mediums or wireless mediums. Those are copper medium, coaxial medium, and electromagnetic wireless transfer. Digital to Analog converter is required for converting the Digital information to Analog or light or electromagnetic signals.
Analog to Digital converter for vise versa.
2. Data Link Layer(DLL):
The data link layer is responsible for the node-to-node delivery of the message. The main function of the DLL is to make sure data transfer is error free from one node to another, over the physical layer.
It is divided into two layers:
Logical Link Control(LLC):
The Logical Link Control(LLC) will perform accumulation and deaccumulation operations to align the DLL data bus width to the Physical layer data bus width.
Media Access Control(MAC):
3. Network Layer:
- Breaking up segments into network packets and reassembling the packets at the receiver end
- Routing packets by discovering the best path across a physical network
4. Transport Layer:
The transport layer takes the data transferred in the session layer and breaks it into segments on the transmitting end. It is responsible to reassemble the segments at receiving end. The transport layer carries out flow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again.
5. Session Layer:
The session layer creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer can also set checkpoints during a data transfer, if the session is interrupted, devices can resume data transfer from the last checkpoint.
6. Session Layer:
The presentation layer prepares the data for the application layer. It defines how two devices should encode, encrypt, and compress data so is recovered correctly on the other end.
7. Application Layer:
The Application layer is the end-user software such as web browsers and email clients. It provides protocols that allow the software to send and receive information and present meaningful data to users. A few examples of application layer protocols are the Hyper Text Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).
Protocols of OSI 7 Layer model is given below:
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