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  1. The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology.The original version of the model defined seven layers.These layers are:
    1.application layer-The application layer is the OSI layer closest to the end user, which means both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component.
    2.presentation layer-The presentation layer establishes context between application-layer entities, in which the application-layer entities may use different syntax and semantics if the presentation service provides a mapping between them.
    3.session layer-The session layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application.
    4.transport layer-The transport layer provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host, while maintaining the quality of service functions.
    5.network layer-The network layer provides the functional and procedural means of transferring variable length data sequences (called packets) from one node to another connected in "different networks".
    6.data-link layer-The data link layer provides node-to-node data transfer—a link between two directly connected nodes. It detects and possibly corrects errors that may occur in the physical layer.
    7.physical layer-The physical layer defines the electrical, optical, and physical specifications of the data connection. It defines the relationship between a device and a physical transmission medium .

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  2. .
    OSI- OPEN SYSTEM INTERCONNECTION MODEL
    OSI model has seven layers which are as follows:-
    1.APPLICATION LAYER: It insures the accuracy of data send by a computer to another computer.
    2.Presentation Layer: this layer insures that in which form the code will be sent from one device to another device.
    3. Session Layer: This layer insures the active connections between the two devices inn a network.
    4.Transport Layer:- This layer insures the transferring of data from one device to another device by dividing the information into the small packets.
    5. Network Layer:- This layer insures the best path between the devices in order to transfer the data in a network.
    6.Data Link Layer: This layer insures the data error checking and provide node to node data transfer in a network.
    7.Physical Layer: This layer insures the hardware that sends and receive the data through a medium in a network.

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  3. OSI stands for Open Systems Interconnection. It has been developed by ISO – ‘International Organization of Standardization‘, in the year 1974. It is a 7 layer architecture with each layer having specific functionality to performed. All these 7 layers work collaboratively to transmit the data from one person to another across the globe.
    1. Physical Layer (Layer 1) : The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for the actual physical connection between the devices.
    2. Data Link Layer (DLL) (Layer 2) : 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.
    3. Network Layer (Layer 3) : Network layer works for the transmission of data from one host to the other located in different networks. It also takes care of packet routing i.e. selection of shortest path to transmit the packet, from the number of routes available.
    4. Transport Layer (Layer 4) : Transport layer provides services to application layer and takes services from network layer. The data in the transport layer is referred to as Segments.
    5. Session Layer (Layer 5) : This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security.
    6. Presentation Layer (Layer 6) : Presentation layer is also called the Translation layer.The data from the application layer is extracted here and manipulated as per the required format to transmit over the network.
    7. Application Layer (Layer 7) : At the very top of the OSI Reference Model stack of layers, we find Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network.




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  4. OSI layer:
    7. Application Layer
    This is the topmost layer in the seven OSI Layers. This is the layer that the end-user (can be a computer programmer, or a regular PC user) is actually interacting with. This layer allows access to network resources.
    6. Presentation Layer
    This is the layer in which the operating system operates with the data. Main functions of this layers includes translation, encryption and compression of data. Basically User interacts with Application layer, which sends the data down to Presentation layer.
    5. Session Layer
    This layer has the job of maintaining proper communication by establishing, managing and terminating sessions between two computers. For example, whenever we visit any website, our computer has to create a session with the web server of that website.
    4. Transport Layer
    This layer has a very important job. It decides how much information should be sent at a time. So, when you are communicating with a website, this layer will decide how much data you can transfer and receive at a given point of time. Also, this layer provides reliable process to process message delivery and error recovery.
    3. Network Layer
    The main job of this layer is to move packets from source to destination and provide inter-networking. This is the layer that the routers operate on. Since routers operate at the network level, hence we can say that the IP address is at the network level.
    2. Data Link Layer
    This layer is responsible for organising bits into frames and ensuring hop to hop delivery. This is the layer on which the Switches operate on. Since routers operate at the network level, hence we can say that the MAC address resides at the data link layer. All the computers in a specific network get plugged inito a switch so that they can communicate with each other.
    1. Physical Layer
    This is the layer on which the real transmission of data bits takes place through a medium. This layer is, as the name suggests, all the physical stuff that connects the computers together.

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  5. OSI layer:
    7. Application Layer
    This is the topmost layer in the seven OSI Layers. This is the layer that the end-user (can be a computer programmer, or a regular PC user) is actually interacting with. This layer allows access to network resources.
    6. Presentation Layer
    This is the layer in which the operating system operates with the data. Main functions of this layers includes translation, encryption and compression of data. Basically User interacts with Application layer, which sends the data down to Presentation layer.
    5. Session Layer
    This layer has the job of maintaining proper communication by establishing, managing and terminating sessions between two computers. For example, whenever we visit any website, our computer has to create a session with the web server of that website.
    4. Transport Layer
    This layer has a very important job. It decides how much information should be sent at a time. So, when you are communicating with a website, this layer will decide how much data you can transfer and receive at a given point of time. Also, this layer provides reliable process to process message delivery and error recovery.
    3. Network Layer
    The main job of this layer is to move packets from source to destination and provide inter-networking. This is the layer that the routers operate on. Since routers operate at the network level, hence we can say that the IP address is at the network level.
    2. Data Link Layer
    This layer is responsible for organising bits into frames and ensuring hop to hop delivery. This is the layer on which the Switches operate on. Since routers operate at the network level, hence we can say that the MAC address resides at the data link layer. All the computers in a specific network get plugged inito a switch so that they can communicate with each other.
    1. Physical Layer
    This is the layer on which the real transmission of data bits takes place through a medium. This layer is, as the name suggests, all the physical stuff that connects the computers together.

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  6. OSI MODEL NETWORKING ( OPEN SYSTEM INTERCONNECT MODEL NETWORKING)
    ( APPLICATION 7 ).This layer provides application service for file transfer E-mail,and other network software service. EX: WWW BROWSER, NFS, TELNET,HHTP,FTP

    ( PRESENTATION 6). This layer formats and encrypts data to be send across a network.
    EX: PICT,JPEG, MIDI,MPEG

    (SESSION 5) . THE SESSION layer set-up coordinate and terminates conversation exchange
    EX: NFS. NETBIOS,RPC,SQL

    ( TRANSPORT 4). Transfer of data between end system end to end recovery and flow control.
    Ex: TCP, UDP

    (NETWORK 3). Routing technoliges creating logical path, known as virtual circuits for transmitting data. EX: DDP,IP,IPX

    (DATA LINK 2). Data link layer is divide into two sub layer . MEDIA ACCESS CONTROL (MAC) LAYER AND LOGICAL LINK CONTROL ( LLC). EX: PPP,FDDI,HDLC,IEEE

    ( PHYSICAL 1). Electrical impuse, light or radio signal. provides the hardware means sending receiving data. EX: FDDI,RJU5,B8ZS.

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