Osi reference model


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Osi reference model

  1. 1. prashob7@outlook.comOSI : Open Systems InterconnectionReference ModelPresented byPrashob P KIn.linkedin.com/in/prashob7APPLICATIONPRESENTATIONSESSIONTRANSPORTNETWORKDATA LINKPHYSICAL
  2. 2. prashob7@outlook.comNeed for a Communication Standard• The communication capability of devices and subsystems andconsistent information methodology are indispensible componentsof future oriented automation concepts.• Communications Protocols define how two or more stationsexchange data using message frames• In order for it to run effectively, defined rules and transfer interfaces needto be used for the communications protocol.• In 1983, the International Organization for Standardization (ISO)developed the OSI reference model ("Open Systems InterconnectionReference Model") for just this purpose.
  3. 3. prashob7@outlook.comOSI Reference Model• The ISO/OSI reference model describes communications between thestations of a communication system.• This protocol defines the elements, structures and tasks required forcommunication and arranges them into seven layers with each layer buildingupon the layer beneath• Each layer has to fulfill specified functions within the communication process.• If a communication system does not require some of those specificfunctions, the corresponding layers have no purpose and are by-passed.• For example PROFIBUS uses layers 1, 2 and 7. In this presentation, profibus istaken as the reference protocol
  5. 5. prashob7@outlook.com7 Layers of OSIApplication Layer Interface to application program with application-orientedcommands (read, write)Presentation Layer Representation (coding) of data for analysis andinterpretation in the next layerSession Layer Establishing and clearing temporary station connections;synchronization of communicating processesTransport Layer Controlling data transmission for layer 5 (transport errors,break down into packets)Network Layer Establishing and clearing connections, avoiding networkcongestionData Link Layer Description of bus access protocol (Medium AccessControl, MAC) including data securityPhysical Layer Definition of the medium (hardware), coding and speed ofthe data transmission
  6. 6. prashob7@outlook.comLayer 1: Physical Layer• The physical layer defines electrical and physicalspecifications for devices• It defines the relationship between a device anda transmission medium, such as a copper or fiberoptical cable.
  7. 7. prashob7@outlook.comPhysical Layer Contd.The major functions and services performed by the physical layer arethe following:• Establishment and termination of a connection toa communications medium.• Participation in the process whereby the communication resourcesare effectively shared among multiple users. Forexample, contention resolution and flow control.• Modulation or conversion between the representation of digitaldata in user equipment and the corresponding signals transmittedover a communications channel. These are signals operating overthe physical cabling (such as copper and optical fiber) or overa radio link.
  8. 8. prashob7@outlook.comLayer 2: Data Link Layer• The data link layer provides the functional andprocedural means to transfer data betweennetwork entities and to detect and possiblycorrect errors that may occur in the physicallayer• In modern practice, only error detection, notflow control using sliding window, is present indata link protocols such as Point-to-PointProtocol(PPP
  9. 9. prashob7@outlook.comData Link Layer Contd.Following are the functions of data link layer:-• Framing• Physical Addressing• Flow Control• Error Control• Access Control• Media Access Control (MAC)
  10. 10. prashob7@outlook.comLayer 3: Network Layer• The network layer provides the functional and proceduralmeans of transferring variable length data sequences from asource host on one network to a destination host on adifferent network (in contrast to the data link layer whichconnects hosts within the same network)• The network layer performs network routing functions, andmight also perform fragmentation and reassembly, and reportdelivery errors
  11. 11. prashob7@outlook.comNetwork Layer ContdThe network layer may be divided into three sub layers:• Sub network access – that considers protocols thatdeal with the interface to networks, such as X.25;• Sub network-dependent convergence – when it isnecessary to bring the level of a transit network upto the level of networks on either side• Sub network-independent convergence – handlestransfer across multiple networks
  12. 12. prashob7@outlook.comLayer 4: Transport Layer• The transport layer provides transparent transfer of data between endusers, providing reliable data transfer services to the upper layers.• The transport layer controls the reliability of a given link through flowcontrol, segmentation/ desegmentation, and error control.• Some protocols are state- and connection-oriented.• The transport layer can keep track of the segments and retransmit thosethat fail.• The transport layer provides the acknowledgement of the successful datatransmission and sends the next data if no errors occurred.
  13. 13. prashob7@outlook.comLayer 5: Session Layer• The session layer controls the dialogues (connections) between computers.• It establishes, manages and terminates the connections between the local andremote application.• It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures.• The OSI model made this layer responsible for graceful close of sessions, which isa property of the Transmission Control Protocol, and also for session checkpointing and recovery, which is not usually used in the Internet Protocol Suite.• The session layer is commonly implemented explicitly in application environmentsthat use remote procedure calls.
  14. 14. prashob7@outlook.comLayer 6: Presentation Layer• The presentation layer establishes context between application-layer entities, inwhich the higher-layer entities may use different syntax and semantics if thepresentation service provides a mapping between them.• If a mapping is available, presentation service data units are encapsulated intosession protocol data units, and passed down the stack.• This layer provides independence from data representation (e.g., encryption) bytranslating between application and network formats.• The presentation layer transforms data into the form that the application accepts.• This layer formats and encrypts data to be sent across a network.• It is sometimes called the syntax layer.
  15. 15. prashob7@outlook.comLayer 7: Application Layer• The application layer is the OSI layer closest tothe end user• the OSI application layer and the user interactdirectly with the software application.• This layer interacts with software applicationsthat implement a communicating component.• Application-layer functions typically includeidentifying communication partners, determiningresource availability, and synchronizingcommunication.•
  16. 16. prashob7@outlook.comApplication Layer Contd.• When identifying communication partners, the application layerdetermines the identity and availability of communication partners for anapplication with data to transmit.• When determining resource availability, the application layer must decidewhether sufficient network or the requested communication exist.• In synchronizing communication, all communication between applicationsrequires cooperation that is managed by the application layer
  17. 17. prashob7@outlook.comTHANK YOUReferenceProfibus InternationalWikiipediaPacontrol.comwww.isa.orh