Layman View of Osi Reference Model

layperson View of OSI Reference Model (By Diganta Deka, Former Student, Proprietor-Trainer East India Technologies, Guwahati. ), diganta. email&160protected com When we whistle about computer lucres and how computers operate in networks, things do non stay on as simple as it seems to be. Here numerous protocols work in tandem for the sake of data integrity during the course of data transfer. To attain things worse thither be a lot of vendors in the foodstuff who provide and produce great telephone number of network hardware and turn on us to social function them.Therefore to provide a solution and to make every(prenominal) these devices communicate in 1984, The International Organization for Standardization (ISO) developed the sacrifice Systems Interconnections (OSI) reference exercise. Basic in ally it described how information is transferred from one networking component to another, from the shoot down when a user enters information using a mouse or a keyboard to whe n that information is converted to electrical or light signals transferred along a piece of wire or radio waves through the zephyr and vice versa.So we can say, OSI reference precedent provides a foundation to use when you are considering what happens among the network components when they talk with all(prenominal) other. ISO developed a seven level model which allowed vendors and network administrators to understand a fixed data transfer and also provided guidelines for implementing new networking standards. Table-1 below briefly describes these moulds, their associated go and protocols supported. Layer thing Service Description occupation The Application layer provides an interface between the communication software program and any other practical application that needs to communicate outside the computer on which the application resides. This layer flirts the serve that directly support applications such as software for blame transfers, database access, and elect ronic 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 school term The Session layer allows two applications on different computers to establish, use, and end a session. This includes the hold up and management of multiple bidirectional cores so that the application can be notified if only some of a series of meanss are completed. This allows Presentation layer to have a seamless view of an incoming stream of data. 4 Transport The Transport layer defines the end-to-end transmission of data between nodes (e. . PCs), including run for control and error recognition and rec all overy. It also repackages long messages when prerequisite into smaller packets for transmission and, at the receiving end, rebuilds packets into the original message. 3 electronic network The web lay er provides routing, logical network addressing, path determination, media/framing translation, frame fragmentation, and over-crowding signaling/control. The routing concepts define how devices route or forward packets to their final destination.Logical addressing defines how each(prenominal) device can have an address that can be utilize by the routing process. Path determination refers to the work done by which all possible routes are learned, but the best route is chosen for use. 2 data Link The Data Link layer packages raw chips from the fleshly layer into frames (logical, structured packets). This layer specifies the device addressing, topology and media access, bit/byte synchronization, flow control, and error detection/recovery services associated with sending frames of data over a material colligate. 1 Physical The Physical layer specifies how bit streams are to be transmitted over a physical link in the network. This includes physical characteristics of transmission medium, including pins, use of pins, electrical, current, encoding, light modulation and the rules for how to air out and deactivate the use of the physical medium. Table-1 Within the network, data traverses a network ken using a process called encapsulation. When an application requires communications resources, the message is handed over to the network pottys application layer.There, the message is processed into a Protocol Data Unit (PDU). Application item header information is wrapped around the data. The resultant PDU is then passed to the heaps presentation 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 wait on Fig-1 The real data transfer process starts from the Transpo rt Layer, where the data is segmental and hence the data is termed as segment in transport layer. When the segments pass on the network layer each segment is upset(a) into packets. As these packets are transferred to Data Link Layer each packet is again broken into frames and in Physical Layer the frames converts into combats. When the bit stream reaches the destination system, the wind 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(prenominal) layer, until the original message is presented to the destination application. Typically, a communication layer does not process, or alter the PDUs content as generated by an beside layer. Information exchange only occurs between peer OSI layers. The peer kindred between OSI layers is illustrated in Figure 2.Illustrated Peer Relationship between OSI Layers Bit shoot Frame packet Segment Data Str eam Data Stream Data Stream Bit Stream Frame Packet Segment Data Stream Data Stream Data Stream Figure-2 Till now we have been talking about the concept croup the OSI reference model, but if we do not discuss about the protocols (protocol is an agree 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 Name of the layer Devices 3 Network Router, Layer3 Switch 2 Data Link Switch, Bridge and NIC 1 Physical Hub, Repeater Table-2 Protocols and the Layers at Which They Function Name 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 few 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 old age we have come across so many network hardware, software or operating systems but everything is manufactured keeping OSI reference model as a benchmark.