OSI MODEL

OSI MODELOpen Systems Interconnection Model

OSI Model

It is a conceptual model that characterizes and standardizes the internal functions of a communication system by partitioning it into abstraction layers. The model groups communication functions into seven

logical layers. A layer serves the layer above it and is served by the layer below it. Two instances at one layer are connected by a

horizontal connection on that layer.

From: en.wikipedia.org

OSI Model - History

In the late 1970s, two projects began independently to define a unifying standard for the architecture of networking systems. One was administered by the ISO, and the other by the CCITT.

In 1983, they were merged to form a standard called The Basic Reference Model for Open Systems Interconnection, or shortly the Open Systems Interconnection Reference Model, the OSI Reference Model, or even just the OSI Model.

It was published in 1984 by both the ISO, as standard ISO 7498, and the ITU-T as standard X.200.

OSI had two major components: an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols.

In this model, a networking system was divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it.



OSI Model

Layer Data unit Function[3] Examples

Hostlayers

7. Application

Data

High-level APIs, including resource sharing, remote file access, directory servicesand virtual terminals

HTTP, FTP, SMTP

6. PresentationTranslation of data between a networking service and an application; includingcharacter encoding, data compression and encryption/decryption

5. SessionManaging communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes

4. Transport SegmentsReliable transmission of data segments between points on a network, includingsegmentation, acknowledgement and multiplexing

TCP, UDP, L2TP

Medialayers

3. NetworkPacket/Datagram

Structuring and managing a multi-node network, including addressing, routingand traffic control

IPv4, IPv6, IPsec, AppleTalk

2. Data link Bit/FrameReliable transmission of data frames between two nodes connected by a physical layer

PPP, IEEE 802.2

1. Physical BitTransmission and reception of raw bit streams over a physical medium

DSL, USB

From: http://blog.buildingautomationmonthly.com/what-is-the-osi-model/

http://haymanezzeldin.blogspot.com/2008/02/scanning-basics.html

From: www.networkworld.com/

From: http://fiberbit.com.tw

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OSI MODEL