Layman View of Osi Reference Model

Layman captivate of OSI Reference Model (By Diganta Deka, Former Student, Proprietor-Trainer East India Technologies, Guwahati. ), diganta. emailprotected com When we talk about electronic computer nedeucerks and how computers operate in networks, things do not remain as dissolvedid as it seems to be. Here numerous protocols work in tandem for the interest of info integrity during the course of entropy direct. To make things worse at that place argon a lot of vendors in the market who provide and begin great number of network hardware and push us to economic consumption them.Therefore to provide a solution and to make all these devices extend in 1984, The International Organization for Standardization (ISO) developed the Open Systems Interconnections (OSI) reference mould. essentially it described how selective discipline is transferred from one networking component to another, from the point when a exploiter enters tuition utilise a mo workout or a keyboard to whe n that information is converted to electrical or light signals transferred along a ready of wire or radio waves through the air and vice versa.So we can buoy say, OSI reference model provides a foundation to use when you are considering what happens amidst the network components when they talk with each other. ISO developed a seven bottom model which allowed vendors and network administrators to understand a stable data transfer and also provided guidelines for implementing new networking standards. Table-1 below briefly describes these bottoms, their associated services and protocols supported. Layer lam Service Description Application The Application layer provides an interface betwixt the communication software and any other application that needs to communicate outside the computer on which the application resides. This layer represents the services that today support applications such as software for file transfers, database access, and electronic mail. 6 Presentation The Presentation layer translates data from the Application layer into an intermediary format, such as ASCII text, EBCDIC text, binary, BCD, JPEG etc.This layer also provides services such as data encryption, and data compression. 5 Session The Session layer allows two applications on different computers to establish, use, and end a session. This includes the temper and management of twofold bidirectional inwardnesss so that the application can be notified if only virtually of a series of messages are completed. This allows Presentation layer to have a seamless view of an incoming stream of data. 4 exaltation The Transport layer arranges the end-to-end contagion of data between nodes (e. . PCs), including flow control and error recognition and rec overy. It also repackages long messages when necessary into smaller packets for transmittal and, at the receiving end, rebuilds packets into the original message. 3 Network The Network layer provides routing, transparent networ k addressing, path determination, media/framing translation, frame fragmentation, and congestion signaling/control. The routing concepts define how devices route or forward packets to their final destination.Logical addressing defines how each device can have an address that can be used by the routing process. avenue determination refers to the work done by which all possible routes are learned, barely the best route is chosen for use. 2 selective information connexion The selective information linkup layer packages raw bits from the physical layer into frames (logical, integrated packets). This layer specifies the device addressing, topology and media access, bit/byte synchronization, flow control, and error contracting/recovery services associated with sending frames of data over a material link. 1 Physical The Physical layer specifies how bit streams are to be transmitted over a animal(prenominal) link in the network. This includes physical characteristics of transmissio n medium, including pins, use of pins, electrical, current, encoding, light modulation and the rules for how to activate and deactivate the use of the physical medium. Table-1 Within the network, data traverses a network stack using a process called encapsulation. When an application requires communications resources, the message is handed over to the network stacks application layer.There, the message is processed into a Protocol Data Unit (PDU). Application specific caput information is wrapped around the data. The resultant PDU is then passed to the stacks video display layer, where additional header information is added. Each subsequent layer in the source systems network stack adds service-specific header information to the PDU, until a fully formatted data frame is presented to the physical layer for transmission onto the communications medium.This encapsulation process is illustrated in Figure 1. Encapsulation Process Fig-1 The real data transfer process starts from the Tr ansport Layer, where the data is segmented and hence the data is termed as segment in transport layer. When the segments reach the network layer each segment is broken into packets. As these packets are transferred to Data touch on Layer each packet is again broken into frames and in Physical Layer the frames converts into Bits. When the bit stream reaches the destination system, the reverse occurs.Each layer in the destination systems network stack analyzes and then strips its associated header information from the message. The resultant PDU is then passed to the next higher layer, until the original message is presented to the destination application. Typically, a communication layer does not process, or distort the PDUs content as generated by an adjacent layer. Information flip-flop only occurs between peer OSI layers. The peer relationship between OSI layers is illustrated in Figure 2.Illustrated Peer Relationship between OSI Layers Bit Stream bound Packet Segment Data Stre am Data Stream Data Stream Bit Stream Frame Packet Segment Data Stream Data Stream Data Stream Figure-2 Till straightway we have been talking about the concept behind the OSI reference model, but if we do not discuss about the protocols (protocol is an agreed set of rules by which devices in a network or number of networks can successfully communicate with each other) and devices that work in each layer of the model then the discussion would remain incomplete.Table-2 and Table-3 respectively represent the devices and the protocols used in various layers in the OSI Reference Model. Devices and the Layers at Which They Function Layer chance upon of the layer Devices 3 Network Router, Layer3 Switch 2 Data striking Switch, Bridge and NIC 1 Physical Hub, Repeater Table-2 Protocols and the Layers at Which They Function visit of the Layers Protocols Application FTP, Telnet, NFS, HTTP, TFTP, DHCP, DNS, VoIP, SNMP, POP3, SMTP Presentation ASCII, HTML, JPEG Session SQL, RPCTransport TCP, UDP, SPX Network IP, X. 25, IPX, Q. 931 Data Link HDLC, Ethernet, LLC, Frame Relay, ATM, Q. 921, FDDI Physical RS-232, V. 35, 10bT, RJ45, G. 703/G. 704 Table-3 In the field of networking there very a couple of(prenominal) people who is not aware of OSI reference model and it is impossible to imagine the world of Information Technology without this model. Over the years we have coiffe across so many network hardware, software or operational systems but everything is manufactured keeping OSI reference model as a benchmark.