OSI Model Layer : A complete Explaination


Open Systems Interconnection LAYERS

The open Systems Interconnection model (OSI) is a conceptual model that standardizes and characterizes the internal functions of a communication system by partitioning it into abstraction layers. The model is a product of the Open systems Interconnection project at the International Organization for Standardization (ISO).

The OSI reference model has seven layers. These were decided on the basis of following principles:

  • A layer should be created where a different level of abstraction is needed.
  • Each layer should perform a well-defined function
  • The laser boundaries should be chosen to minimize the information flow across the interface.

OSI model itself is not a network architecture. It does not specify the exact services and protocols to be used in each layer. It just tell what each laser should do. It provides a basis for coordinating the development of a standard that would facilitate a flexible interconnection of systems.

The seven layers of OSI model are:

  • Physical layer
  • Data link layer
  • Network layer
  • Transport layer
  • Session layer
  • Presentation layer
  • Application layer
S.No. Layer Description Device Protocol
1 Physical Transmits data over physical medium Multiplexer and repeater, hub, Amplifier, Oscilloscope IEEE802, IEEE802.2, ISO2110, ISDN
2 Data link Packages raw bits into frames and includes a cyclical redundancy check (CRC) Switch, bridge and brouter, NIC LIC
3 Network Handles addressing, translates logical addresses and names to physical addresses, routing and traffic management Router and Brouter IP, IPX, NW Link, NetBEUL
4 Transport Repackages messages into smaller formats, provides error free delivers and error handling functions Gateway NetBEUI, TCP, SPX and NW Link, ARP, RARP, NETBios
5 Session Allows two applications to communicate over a network by opening a session and synchronizing the involved computers Gateway NetBios, RPC
6 Presentation Performs protocols conversion, encryption and data compression Gateway and redirectors AFP, TDI, SMB, NCP
7 Application Provides network access for applications, flow control and error recovery Gateway SMTP, ETP, SNMP, Telnet, Appletalk, DNS,TFTP, MINE, LOGIN, NFS, BOOTP

Important Questions for IT Officer