one of the first topic that faces any one beginning network career is osi model , i will try to make it very simple , so i made a video to approach osi model concepts and layers.
after seeing the video lets go more deep in osi model
The Open Systems Interconnection (OSI) reference model provides a means of
describing how data is transmitted over a network. The model addresses
hardware, software, and data transmission. This topic describes the purpose of
the OSI model
The OSI reference model provides a number
of benefits in understanding how networks function, by doing the following:
- Reducing complexity: The
OSI model breaks network communications into smaller, simpler parts.
- Standardizing interfaces: The
OSI model standardizes network components to allow multiple-vendor development
and support.
- Facilitating modular engineering:
The OSI model allows different types of network hardware and
software to communicate with one another.
- Ensuring interoperable
technology: The OSI model prevents changes in one layer
from affecting the other layers, allowing for quicker development.
- Accelerating evolution: The
OSI model provides for effective updates and improvements to individual components
without affecting other components or having to rewrite the entire protocol.
- Simplifying teaching and
learning: The OSI model breaks network communications
into smaller components to make learning easier
The OSI Model
Layers and Their Functions
The OSI isn’t a physical model. it's a set
of guidelines that application developers can use to create and implement
applications that run on a network.
The OSI has seven different layers, divided
into two groups. The top three layers define how the applications within the
end stations will communicate with each other and with users. The bottom four
layers define how Data is transmitted end to end.
The OSI reference model has seven layers:
-
Application layer
(layer 7)
-
Presentation layer
(layer 6)
-
Session layer
(layer 5)
-
Transport layer
(layer 4)
-
Network layer
(layer 3)
-
Data Link layer (layer
2)
-
Physical layer
(layer 1)
The Application Layer
The application layer is the OSI layer that
is closest to the user, acting as an interface between the actual application
program—which isn’t part of the layered
structure—and the next layer down.
This layer provides network services to the
applications of the user, such as e-mail, file transfer, and terminal
emulation.
The Application layer is also responsible
for identifying and establishing the availability of the communication partner
and determining whether sufficient resources for the intended communication
exist.
The Presentation Layer
The Presentation is responsible for data
translation and code formatting. Tasks like data compression, decompression,
encryption, and decryption are associated with this layer.
The Session Layer
The Session layer is responsible for
setting up, managing, and then tearing down sessions between Presentation layer
entities (keeps different applications’ data separate from other applications’
data.).
For example, web servers have many users,
so there are many communication processes open at a given time. It is
important, then, to keep track of which user communicates on which path.
The Transport Layer
The transport layer segments data from the
system of the sending host and reassembles the data into a data stream on the
system of the receiving host.
The transport layer establishes, maintains,
and properly terminates virtual circuits. Transport error detection and
recovery and information flow control ensure reliable service.
The Network Layer
The network layer provides connectivity and
path selection between two host systems that may be located on geographically
separated networks.
The Data Link Layer
The data link layer defines how data is
formatted for transmission and how access to the physical media is controlled.
This layer also typically includes error detection and correction to ensure
reliable delivery of the data.
The Physical Layer
the Physical layer does two things: It
sends bits and receives bits.
This layer defines the electrical,
mechanical, procedural, and functional specifications for activating,
maintaining, and deactivating the physical link between end systems.
Characteristics such as voltage levels,
timing of voltage changes, physical data rates, maximum transmission distances,
physical connectors, and other similar attributes are defined by physical layer
specifications.
