A walm welcome to you!!!

Let us share something worth that will help all of us to increase our knowledge orientation in the huge and ever expanding world of Networking!

I have created this blog to help each and everyone who visits this blog to get himself acquainted with new technologies, recent developments in the world of technology....

I hope you will help me share my knowledge with you....!!!!

Thursday, February 16, 2012

OSI, IP Suite & the DoD Model-I (OSI Model)

Now, lets turn to the 'bases' on which the whole Internet functions. These are the core concepts of the 
Internet and one must know how the Internet functions. I have broken the whole post into 
three parts- 
(i) The OSI Model
(ii) The IP Suite
(iii) The DoD Model

I. The OSI Model (Open Systems Interconnection)

1. Introduction
   (i) A networking model introduced by the International Organization for Standardization (ISO)
       to promote multivendor interoperability.
   (ii) OSI is a seven-layered conceptual model consisting of the application, presentation,
        session, transport, network, datalink, and physical layers.

2. Layers of OSI Model as defined by the International Organisation for Standardisation (ISO)

(i) Application Layer

Layer 7 provides an interface between the communications software and any applications
that need to communicate outside the computer on which the application resides. It 
also defines processes for user authentication.               

(ii) Presentation Layer

The presentation layer formats data received from the application layer  before passing
 it to the layers. Encryption also is defined by OSI as a  presentation layer service.

(iii) Sessions Layer

The session layer defines how to start, control, and end conversations (called sessions). 
This includes the control and management of multiple bidirectional messages so
 that the application can be notified if only some of a series of messages are completed.

(iv) Transport Layer

The transport layer works with the network layer to package and transfer data that it 
receives from the session layer. Layer 4 focuses on issues related to data delivery to
another computer error recovery and flow control.

(v) Network Layer

The network layer defines three main features: logical addressing, routing (forwarding)
and path determination. The routing concepts define how devices (typically routers)
forward packets to their final destination. Logical addressing defines how each device 
can have an address that can be used by the routing process. Path determination      
refers to the work done by routing protocols by which all possible routes are learned, but
the best route is chosen for use.

(vi) Data-Link Layer

The data link layer defines the rules (protocols) that determine when a device can send
data over a particular medium. Data link protocols also define the format of a header
and trailer that allows devices attached to the medium to send and receive data 
successfully. The data link trailer, which follows the encapsulated data, typically defines
a Frame Check Sequence (FCS) field, which allows the receiving device to detect the transmission errors

(vii) Physical Layer

This layer typically refers to standards from other organizations. These standards deal 
with the physical characteristics of the transmission medium, including connectors, 
pins, use of pins, electrical currents, encoding, light modulation, and the rules for how to activate and deactivate the use of the physical medium.

I will be again going into the depths of the OSI model, how devices on the network 
operate at different layers of this model in the next few weeks. This was only the overview.
I hope you all atleast got the idea as to what is an OSI model. These layers are so crucial
that no communication can be established over the Internet if anyone of these layers are 
absent (if we take this model into consideration...about IP Suite and DoD Model, I will 
be writing soon).




  1. hey sid dis post is a bit heavy to understand :(

  2. Hmmm, let me explain. OSI model tells you how you communicate over the internet. Take the example of my own blog. When you enter 'http://lifedownloadedfromheavens.blogpot.com' in the address bar of your browser, how do you get the web page? The OSI model talks on this and it is the core concept which shows you how the Internet works.First, your computer sends data over the physical layer (cables,routers etc), then the data goes to the data link layer and thereafter the layers above it in a hierarchical order. When you receive the reply from the other side, then the physical layer comes at the end. I hope you got it. Thank you very much for your query, if you find any explanation unsatisfactory, get back to me!

  3. yep got it now :)