Open Systems Interconnections Model - 7 layers
- 1. OSI Model
- 2. Index What is OSI Model Different layers of OSI Practical Advantages of using OSI Limitations Of OSI
- 3. What is OSI Model ? It basically defines and used to understand how data is transferred from one computer to another computer in a communication network. In more simpler Terms if two computer is connected via LAN cable and therefore computer are sharing information through NIC(network interface card). But What if one computer is running mac OS and other running Windows OS so here the importance of OSI comes into picture. So in order to establish a successful Communication between computers, networks or different architecture we require a 7 layer architecture which is called OSI(Open System Interconnection) model.
- 4. It was Developed by ISO in 1984. The seven layers represents namely: Application layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical layer
- 5. Application layer is used by network application as it contain certain protocols which those application uses to work correctly in a network or internet. Web browser such as chrome, Firefox ,ie ,Edge,Safari,etc uses Application Layer protocols such as HTTP &HTTPs to do web surfing. There are dozens of protocols that network applications follows which all sums up to form the application layer like For sending and receiving emails SMTP protocol is followed File transfer is done via FTP protocols. Virtual Terminals is done By following Telnet Protocols. So Application layer Provides services for network application using different protocols to perform user activities such as web surfing, File Transfer,etc. Application Layer
- 6. So it receives data from application layer in the form of character and number. So basically it performs three major functions such as: I. Data Translation : Data are converted into computer understandable bits format. II. Data Compression : Data are compressed by reducing the no. of bits so as to decrease the size of the data to improve the transmission speed. Based om the type of compression it is of two types : Lossy and Lossless. III. Data Encryption : Data are encrypted to enhance the security of sensitive data. So in the sender side the data are encrypted and at the receiver side the data are decrypted. SSL(Secure Socket Layer) protocols are used for encryption and decryption. Presentation Layer
- 7. Process involved in Presentation Layer
- 8. It helps in Setting up & managing the connection enabling sending and receiving of data followed by termination of connection or session. Session layers uses 1. APIs(Application Programmable interface) : like NETBIOS is an example of API which is basic I/P O/P system which allows different application to communicate with one another. 2. Authentication and Authorization :To connect to the server we need this to access the files from a server. I. So in authentication the server verifies the identity by providing username and password. II. Once the authentication is done then serves does authorization in which it checks for the accessible data for that user and shows those data only on request. It also keep tracks on the files which are downloaded for example if we open any webpage on a web browser it requests for that webpage from the web server so it contains texts,images,etc as a separate files. So it gets downloaded via web Server in the form small data packets and session layers keep track on which data packet belongs to which file either text file or image file. So it helps in Session Management. Session Layer
- 9. Functions done by Session Layer
- 10. It controls the Reliability of communication through : 1. Segmentation : It Converts the data received from transport layer into segments. Each segment contains a source and destination port no. And Sequence no. Port no. Helps to direct each segment to the correct application and sequence no. Helps to reassemble the segments into correct order to form the correct message at the receiver. 2. Flow control : It Control the amount of data being transmitted. 3. Error Control : If some data doesn't arrive at destination then transport layer uses automatic repeat request to retransmit the loss or corrupted data. A group of bits called checksum is added after every segments to find out the received corrupted segment. Protocols of transport layers are TCP(Transmission Control Protocol) and UDP .(User Datagram protocol) Services of transport layer are connection Oriented transmission or Connectionless transmission. Transport Layer
- 11. Services and Protocols of Transmission layer
- 12. Transport layer Passes the data Segments to the Network layer. Network layer works for the transmission of received data segments from one computer to another located at different networks. Data units are called packets Function of network layer are : 1. Logical Addressing : Ip Addressing(ipv4 or ipv6) done in network layer is called logical addressing. Every Computer has its separate ip address ,network layer assigns senders and receiver ip address to each segment to form an IP packet. It insures that each data packet reach to the correct destination. 2. Routing : It is a method of moving data packet from source to the destination and it is based on logical address format of ipv4 or ipv6 and mask . 3. Path Determination :Choosing the best path for data delivery between sender and receiver is called path determination. Network Layer
- 14. One of the function of Network Layer
- 15. It receives the data packets from the network layer Data packets contains IP address of the sender and the receiver. So there are two kinds of addressing : 1. logical addressing – It is done at the network layer where the sender's and receiver's ip address are assigned to the each segment to form a data packet. 2. Physical Addressing – It is done at the data link layer where Mac address of sender and receiver are assigned to each data packet to form frame. Data unit in a data link layer is called frame. Data link layer is embedded as software in network Interface card(NIC)of a computer and provides means to transfer data from one computer to another via a local media. Therefore it performs two basic function : 1. It allows upper layer of OSI model to access Media using techniques such as framing 2. It controls how data is placed and received from the media through media access control. Data Link Layer
- 16. Data Link Layer Involves
- 17. Till now data are in binary form so physical layer converts these binary bits into signals and transmits over local media.it can be of electrical signal in case of LAN wire, light signal in case of optical fiber or radio signal in case of air. So at the receiver part these signals are again converted into bits and pass it into data link layer as a frame. Frame is further decapsulated as data moves to the higher layer. Finally data is moved to the application layer and its protocols makes the senders message visible at the receiver side. In this way OSI model helps in transmission of data between distant hosts. Physical Layer
- 20. Layers in the OSI model architectures can be distinguished and every layer has its own importance according to their interfaces, services, and protocols. The OSI divides the all process of data communication into simpler and smaller It supports both connection-oriented services and connectionless services. It distinctly separates services, interfaces, and protocols. Hence, it is flexible in nature. Protocols in each layer can be replaced very conveniently depending upon the nature of the network. It is a generic model and acts as a guidance tool to develop any network model. Advantages of Using OSI model
- 21. It is purely a theoretical model that does not consider the availability of appropriate technology. This restricts its practical implementation. The launching timing of this model was inappropriate. When OSI appeared, the TCP/IP protocols were already implemented. So, the companies were initially reluctant to use it. The OSI model is very complex. The initial implementation was cumbersome, slow and costly. Though there are many layers, some of the layers like the session layer and presentation layer have very little functionality when practically deployed. Though there are many layers, some of the layers like the session layer and presentation layer have very little functionality when practically deployed. Limitations of OSI Model