NETWORKINGStandards and Protocols
STANDARDS AND PROTOCOLSThe OSI Model
WHAT IS THE OSI MODEL?
WHAT IS THE OSI MODEL? OSI Stands for Open Systems Interconnection. The OSI model is a layered, abstract
description for communications and computer network protocol design.
The Open Systems Interconnection model is a set of standard specifications that allows various computer platforms to communicate with each other openly.
It is concerned with the interconnection between systems – the way the systems exchange information – and not with the internal functions of the particular system
WHAT IS THE OSI MODEL? It divides the network architecture into seven
layers:1. Physical2. Data Link3. Network4. Transport5. Session6. Presentation7. Application
WH
AT IS THE O
SI MO
DEL?
Each of these different layers has its own set of functions and only communicates with the layers directly above and below and with its opposite layer on other computers.
WHY A LAYERED MODEL?
WHY A LAYERED MODEL?Change:
When changes are made to one layer, the impact on the other layers is minimized.
A layered model defines each layer separately. The layered approach reduces a very complex
set of topics, activities, and actions into several smaller, interrelated groupings.
This makes learning and understanding the actions of each layer and the model generally much easier.
Troubleshooting efforts to be pinpointed on the layer that is the suspected cause of the problem.
WHY A LAYERED MODEL?Standards:
Probably the most important reason for using a layered model is that it establishes a prescribed guideline for interoperability between the various vendors developing products that perform different data communications tasks.
Remember, though, that layered models, including the OSI model, provide only a guideline and framework, not a rigid standard that manufacturers can use when creating their products.
THE SEVEN LAYERS OF THE OSI MODEL
PHYSICAL LAYER
PHYSICAL LAYER The Physical layer is the lowest or first layer
of the OSI Model. This layer contains the physical networking medium, such as cabling, connectors, and repeaters.
The Physical Layer defines: Physical network structures Mechanical and electrical specifications for using
the transmission medium Bit transmission encoding and timing rules
PHYSICAL LAYER The following network connectivity hardware
are normally associated with the OSI physical layer: Network interface boards (NIC, adaptors, and so
on) Hubs, and repeaters that regenerate electrical
signals Transmission media connectors (cables, BNC
connectors, etc) Modems and codec's, which perform digital
analogue conversions.
DATA LINK LAYER
DATA LINK LAYER The second layer of the OSI Model, the Data
Link Layer, controls communications between the Network layer and the Physical layer.
Its primary function is to divide data it receives from the Network layer into distinct frames that can be transmitted by the Physical layer.
DATA LINK LAYER The basic purposes of the data link layer
protocol implementations are: Organise the physical layer’s bits into logical
groups of information called frames Detect and correct errors Control data flow Identify computers on the network
NETWORK LAYER
NETWORK LAYER The primary function of the Network Layer,
the third layer in the OSI Model has the main objective of moving data to specific network locations.
NETWORK LAYER Decides on the best route for the data to take
from sender to receiver. Similar to what the data link layer
accomplishes, however, data link layer addressing only operates on a single network
NETWORK LAYER The network layer describes methods for
moving information between multiple independent networks, called internetworks.
TRANSPORT LAYER
TRANSPORT LAYER The transport layer provides enhancements
to the services of the network layer. Its main tasks is to ensure that data sent
form one computer arrives reliably, in the correct sequence and without errors at the receiving computer.
TRANSPORT LAYER This layer is the last chance for error
recovery. The transport layer is also responsible for flow control.
It’s here that there rate of transmission is determined, based on how fast the receiving computer can accept the data packets being sent to it.
Data on the sending computer is broken down into packets that are the maximum size that the type of network can handle.
SESSION LAYER
SESSION LAYER The Session Layer is responsible for
establishing and maintaining communication between two nodes on the network.
SESSION LAYER The term session refers to a connection for
data exchange between two nodes. Often, this layer also helps the upper layers
identify and connect to the services that are available on the network.
If a communication session is broken, is the session layer that determines where to restart the transmission once the session has been reconnected
SESSION LAYER This layer is also responsible for determining
the terms of the communication session – it will determine which computer or node can communicate first and for how long
It is sometimes known as the ‘traffic cop’ of the network
PRESENTATION LAYER
PRESENTATION LAYER The Presentation Layer serves as a translator
between the application and the network. At the Presentation layer, data become
formatted in a schema that the network can understand; this format varies with the type of network used.
The Presentation Layer manages data encryption and decryption, such as the scrambling of system passwords.
APPLICATION LAYER
APPLICATION LAYER The top or seventh layer of the OSI Model is
the Application layer. The Application provides interfaces to the
software that enable programs to use network services.
APPLICATION LAYER The term “Application Layer” does not refer
to a particular software application, such as Microsoft Word, running on the network.
Instead, some of the services provided by the Application layer include file transfer, file management, and message handling for electronic mail.
APPLICATION LAYER Examples of common functions include:
Protocols for providing remote file services, such as open, close, read, write, and shared access to files
File transfer services and remote database access
Message handling services for electronic mail applications
Locate resources on a network A uniform way of handling a variety of system
devices