Learn OSI Network Model

The Open Systems Interconnection (OSI) Reference Model, also called OSI Reference Model or just OSI Model, roughly translated, is the reference model of Open Systems Connectivity; it is a design based on the principles of an abstract digital communications connection between computers and the network protocol design to implement the connection. This model was developed as part of plans for open systems connectivity (Open Systems Interconnection) by ISO; IUT-T initiated. It is also known as the seven layers of the OSI model. (According to the Wikipedia).

  1. Function OSI model:

    The OSI model divides the functions of a protocol into a series of layers. Each level has a characteristic story that it uses, each level interacts only with lower levels, while only higher levels can use its functions. An installed system includes a protocol layer above the chain called the "stack" (protocol stack). Protocol stacks can be installed on the hardware, or software, or a combination of both. Typically, only the lower level are installed in the hardware, while the other floors are installed in the software.
     
  2. The advantage of the OSI model

    • Split complexity of network operation into the simple task.
    • Allow designers to develop the ability to function in each module.
    • Provide the ability to define interfaces with high compatibility, the ability to "plug and play" and integrate multi-vendor products.
     
  3. OSI model structure

    The OSI model consists of seven layers, each layer performing separate functions in networking activities. Among them: the fourth (Transport) layer defines the settings on the device end hardware to connect and exchange data; the third (Network) layer is for application development, user interface.

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    1. Physical layer

      The Physical layer defines all the electrical specifications and physical devices. This includes the layout of pins (pin), the voltage, and the specification of cables (cable). The Physical layer devices including Hub, repeater (repeater), network adapters (network adapter) and set host channel adapter (Host Bus Adapter (HBA)). (The HBA is used in storage area networks (Storage Area Networks).)

      The functions and basic services performed by the Physical layer include:

      • Set the circuit breaker or electrical connections (electrical connection) to a [[transmission medium [[File: | media]] communications (transmission medium).
      • Participation in the process whereby the communication resources are effectively shared among multiple users. Such dispute resolution resources (contention) and flow control.
      • Modulation (modulation), or change between performance data (digital data) of the user equipment and the corresponding signals are transmitted through communication channels (communication channel).

      Cable (bus) SCSI Parallel operation of this floor. Many different standards for Ethernet Physical layer is also in this layer; Active Ethernet Physical layer to the Data Link layer into one. The same thing happens to the internal network such as Token Ring, FDDI and IEEE 802.11.
       
    2. Data Link layer

      Data Link layer provides the functional means and processes to transfer data between network entities, can detect and fix errors in the Physical layer, if any. The addressing physical nature, in other words address (MAC address) is hard-coded into the network card (network card) when they are produced. The system does not identify the address class (flat scheme). Note: The most typical example is Ethernet. Other examples of data link protocols (data link protocol) is the protocol HDLC; ADCCP for point-to-point network or a packet-switched network (packet-switched networks) and Aloha protocol for local network. In the local area network standard IEEE 802, and a network of other standards, such as FDDI, Data Link layer can be divided into the 2 levels: the MAC (Media Access Control - Access Control line) level and the LLC (Logical Link Control - Logical Link Control) IEEE 802.2 standard layer. 
      The Data Link layer is for the bridge (bridge) and switches (switches) activities. The connectivity provided between the network nodes are connected together within the network. However, it is reasonable to argue that this device actually belongs to the layer more appropraitely under 2.5 but not the second layer.
       
    3. Network layer

      The Network layer provides the function and process for transferring the data series varied in length, from a source to a destination via one or more networks while maintaining the quality of service (quality of service) that requires the Transport layer. The Network layer performs the routing function. The Routing device (router) operates in this layer, sending data throughout the extended network, making the network link becomes feasible (there are switches (switch) third layer, also called IP switches). This is a positioning system logical address (logical addressing scheme), the value chosen by the network engineer. This system is the structured pedigree. Typical examples of a 3-layer protocol is the IP protocol.
       
    4. Transport layer

      The Transport layer provides transparent transfer of data between end-users, so that the upper floors are not interested in the provision of data transmission services reliably and efficiently. The Transport layer controls the reliability of a given connection. A number of protocol-oriented and connection status (state and connection orientated). This means that the Transport layer can monitor packets and retransmit those that fail. A typical example of the 4-layer protocol is TCP. This layer is where the messages are converted into TCP or UDP packets. On the fourth layer is the address; an address is considered to include the port, ports distinguish address swap applications.
       
    5. Session layer

      The session layer controls conversations between computers. This layer's setup manages and ends the connection between local applications and remote applications. This layer also supports full duplex operation (two-way) or half duplex (one-way) or simplex (only one way) and sets the marking process completed (checkpointing). It helps to achieve faster communication when an error occurs, because the point was marked complete - delayed (adjournment), end (termination) and reboot (restart). The OSI model made this layer responsible for the "light switches" (graceful close) sessions (a characteristic of the transport control protocol TCP) and responsible for checking and recovery sessions, this is the generally not used in the TCP/IP protocol.
       
    6. Presentation layer

      The Presentation layer acts as the data on the Network layer. This transfers duty service data sent from the Application layer into a common formate. And at the receiving computer, this class is moved from formate general format of the Application layer. The class can implement the following functions: Translation of characters from the ASCII code to/from EBCDIC; Data Conversion, for example from integer to floating point numbers; Data compression to reduce the amount of data transmitted over the network and encryption & decryption of data to ensure network security.
       
    7. Application layer

      The Application layer is the layer closest to most users. It provides a means for users to access information and data on the network through the application program. This layer is the main interface for users to interact with applications, and through it to the network. Some examples of applications in this layer include Telnet, File Transfer Protocol (FTP) and the email communications protocols SMTP, HTTP, Mail remote X.400.

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