OSI Model:
The OSI Model is a conceptual framework used to describe the functions of a Networking system. The concept of a Seven-Layer model was provided by the work of Charles Bechman at Honeywell Information Systems. Various aspects of OSI design evolved from experience with the NPL Network, ARPANET, CYCLADES, EIN and International Networking Working Group (IFIPWG6).
We can only understanding these layers from the top down. The uppermost layer engages the most with the end user, while the layers below it have less interaction. In contrast, the bottom layer has the least connection with the end user.
- Hubert Zimmermann was the one who developed OSI in the year 1976. and he then worked for France Telecom from 1980 through 1986. and he created and promoted the OSI reference model which became a popular way to describe Network protocols.
- OSI models were developed by ISO in 1984 and it is now considered an Architecture model for inter-computer communication.
- This model is developed by OSI to ensure National and worldwide data communication systems must be developed that are compatible to communicate with each other ISO has developed a standard.
- ISO Stands for ‘ International Organisation of Standardization.
Advantages of OSI MOdel:
- It is a truly generic Model and it is considered a Standard Model in Computer Networking.
- Layers in OSI Model architecture are distinguished according to the services, interfaces and protocols.
- It supports connection-oriented as well as connectionless services.
- It follows the divide and conquer technique.
- this layered architecture follows the abstraction principle.
- It is more secure and adaptable than having all services bundled in a single layer.
Disadvantages:
- It doesn’t define any particular protocol.
- It may sometimes be difficult to fit a new protocol in this Model.
- There is some dilation of services at various layers.
- There is also Interdependence among the layers.
Layers of OSI Model:
- Physical Layer
- Datalink Layer
- Network Layer
- Transport Layer
- Session Layer
- Presentation Layer
- Application Layer
1. Application Layer:
It enables the user to access Network resources. used by network apps like Chrome, Firefox etc. All Protocols HTTP, HTTPS, FTP etc come under this. Human-computer interaction layer. Where applications can access the network services.
2. Presentation Layer:
It is concerned with syntax and sematcs of the information exchanged between two systems. Ensure the data in usable format and it is where data encrypted occurs.
Service Provide by Presentation Layer:
- File Transfer and Access Management (FTAM)
- Mail Services.
- Directory Sevices.
Translation: This step helps the device to translate the information to recievers device.
Encryption: This step makes the information into unreadable formats untill is raches the end device.
Compression: This step helps to cokpress the data. By compressing the data can be transferred faster.
3. Session Layer:
Session Layer can be maintains connections is responsible for controlling ports and sessions. It establishes maintins and synchronizes the interaction among communicating devices.
- It helps the communication between two devices without any other distubunces.
- It allows some time to communicate between that device untill communicate or sharing information to that device.
- It also tells how long communicate needed to share information.
4. Transport Layer:
It is rsponsible for process to process delivery of the entire message.
Services:
Port Addressing:
Before sharing or recieving on information bothe the devices should known each other ort number. This helps to reach the may to exact end device that we beed ti send.
Segmentation reassembly:
If the message is too big it con’t send as it is. It helps the message to break into small segments and send to end device. This end devices recieves information in small bits and then it reassmble it into readable form.
Connection Control:
It can share information whether the two devices are connected or connectionless.
End to End flow control:
It transmits the data at such a speed that receives end sender will not face any problems.
Error Control:
It retransmitts the last segments and it uses TCP or UDP.
5. Network Layer:
It is responsible for the delivery of data from the source to the destination network. In both devices, logical addresses are mentioned. It has a source IP address and a destination IP address. This helps to share the information easily. It also finds the best route to transfer data between two devices. In this layer, information is converted into packets.
6. Datalink Layer:
This layer provides node-to-node data transfer links between two directly connected nodes. It groups information bits and frames it as a full single MAC. Here switches are used and the MAC addressing is done to every data packet. flow control, Error control, and Access control, Also known as Logical link control.
7. Physical Layer:
It converts the digital bits into electrical, radio or optical signals based on their connection. Bit rate control is down the physical layer and may define transmission made as a simple duplex.