OSI Model Explained
OSI Model or Open System Interconnection is conceptual model of network structure given by ISO (International Organization for Standardization). This model is to guide developer and network community for how stuff work inside network model. This structure is divided in Seven layers known as seven layers of OSI model. This was deloped by representatives of major computer and telecommunication companies beginning in 1983.The main concept of OSI is that the process of communication between two endpoints in a telecommunication network can be divided into seven distinct groups of related functions, or layers. Each communicating user or program is at a computer that can provide those seven layers of function.
These are seven layers of OSI Model.
7. Application layer
Application layer is closest layer to end user. This is the layer at which communication partners are identified network capacity is assessed and that creates a thing to send or opens the thing received. (This layer is not the application itself, it is the set of services an application should be able to make use of directly, although some applications may perform application layer functions.) Application layer provides services to the software through which the user requests network services. Your computer application software is not on the Application layer. This layer isn't about applications and doesn't contain any applications.
Layer 7 Application examples include WWW browsers, NFS, SNMP, Telnet, HTTP, FTP
Layer 7 Application examples include WWW browsers, NFS, SNMP, Telnet, HTTP, FTP
6. 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 big mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units, and passed down the protocol stack.This layer is concerned with data representation and code formatting.This layer provides independence from differences in data representation
Layer 6 Presentation examples include encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI.
5. Session layer
The Session layer establishes, maintains, and manages the communication session between computers.This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
Layer 5 Session examples include NFS, NetBios names, RPC, SQL.
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 via one or more networks, while maintaining the quality of service functions.The functions defined in this layer provide for the reliable transmission of data segments, as well as the disassembly and assembly of the data before and after transmission.This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
Layer 4 Transport examples include SPX, TCP, UDP.
3. Network layer
This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.This layer handles the addressing and routing of the data.
Layer 3 Network examples include AppleTalk DDP, IP, IPX.
2. Data-link layer
As its name suggests, this layer is concerned with the linkages and mechanisms used to move data about the network, including the topology, such as Ethernet or Token Ring, and deals with the ways in which data is reliably transmitted.The data link layer provides node-to-node data transfer.At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization.
Layer 2 Data Link examples include PPP, FDDI, ATM, IEEE 802.5/ 802.2, IEEE 802.3/802.2, HDLC, Frame Relay.
1. Physical layer
The Physical layer's name says it all. This layer defines the electrical and physical specifications for the networking media that carry the data bits across a network.This layer conveys the bit stream - electrical impulse, light or radio signal — through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
Layer 1 Physical examples include Ethernet, FDDI, B8ZS, V.35, V.24, RJ45.
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