OSI, when systems come easy and friendly

When it comes to standardizations, and you love networking, then it comes to OSI model, The Open Systems Interconnection.

OSI model is a product of the Open Systems Interconnection effort at the International Organization for Standardization.

Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors

 

It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Such communication functions are grouped into logical layers, A layer serves the layer above it and is served by the layer below it.

 

Work on a layered model of network architecture was started, and the International Organization for Standardization (ISO) began to develop its OSI framework architecture. 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.

The concept of a seven-layer model was provided by the work of Charles Bachman, Honeywell Information Services. Various aspects of OSI design evolved from experiences with the ARPANET, The new design was documented in ISO 7498 and its various addenda.

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.

The OSI standards documents are available from the ITU-T as the X.200-series of recommendations. Some of the protocol specifications were also available as part of the ITU-T X series. The equivalent ISO and ISO/IEC standards for the OSI model were available from ISO as the ISO/IEC JTC 1

OSI Layers

A simple description of OSI model is in the below table, According to the recommendation of X.200, there are seven layers, labeled 1 to 7

On the other hand, the seven layers of the OSI model can be divided into two groups:- upper layers (layers 7, 6 & 5) and lower layers (layers 4, 3, 2, 1). The upper layers of the OSI model deal with application issues and generally are implemented only in software. The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are implemented in hardware and software.

Best Reference

it comes to me the memories of the best book that can talk about the OSI model and the other "now" adopted model which it is TCP/IP

McGraw - Data Communication and Networking

3th Ed [Behrouz A. Frouzan]

McGraw - Data Communication and Networking

4th Ed [Behrouz A. Frouzan]

Why TCP/IP

The TCP/IP protocol suite was developed prior to the OSI model. Therefore, the layers in the TCP/IP protocol suite do not exactly match those in the OSI model, the original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCPIIP is compared to OSI, we can say that the host-to-network layer is equivalent to the combination of the physical and data link layers. The internet layer is equivalent to the network layer, and the application layer is roughly doing the job of the session, presentation, and application layers with the transport layer in TCP/IP taking care of part of (the duties of the session layer).