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
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).
hey sid dis post is a bit heavy to understand :(
ReplyDeleteHmmm, 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!
ReplyDeleteyep got it now :)
ReplyDelete