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
|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|