Categories: IT Officer

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