Ccna

1-Application Layer

It provides a real interface between the computer application and the network. This layer
the one closest to the user. Only this layer does not provide services to other layers.
The application layer is the program that will use the network service. This layer meets the user’s requirements. For example, a database application or e-mail application, etc. as.

2-Presentation Layer

In the presentation layer, the data is translated. Presentation Layer Sends data to the application layer. In this layer, arrangements are made about the structure and form of the data.
The format of the data in the presentation layer is determined. In addition, the data is encrypted and opened in this layer. In this layer, compression of the data is done.

The task of each layer is to provide service to a higher (higher) layer. Two computers
in the communication between the layers respectively; At the same time, layers at the same level do not directly communicate, but a virtual communication occurs between them.
Figure: Between Two Computers; The relationship between layers real (vertical) and virtual (horizontal)

The data is divided into packets before data is transmitted from one layer to another. The packet is a volume of data used to transfer data from one device to another. Additional information (formatting or addressing) is added to the package in each layer.
The transmission of the data is from the upper layer to the lower layer. Data transmission via cable
by layer. On the other computer, the data that is met by the physical layer first moves to the upper layers.

OSI Model
OSI (Open Systems Interconnection) model ISO (International Standards Organization)
and the way I work between the two computers. First
This standard, which was introduced in 1978, was revised in 1984 and
(Open System Interconnect) as a reference model. Model widely
and has been a guideline for networking.
The OSI Model is specific to any hardware or network. The aim of the OSI network
it provides the use of architects and protocols as a network product business.
ISO standards follow a complex path while maintaining business on the network. ISO standard
the new layer (subroutine). The following seven layers as OSI models are:

MODUL 1: Network Basics

• Basic knowledge.
• To explain the layered model.
• Describe the OSI reference model.
• Describe the network specificity of the layers.
• Explain the Cisco Three-Layer Model.
• Connect Cisco devices.

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Cisco © produces network devices such as Hub, Router, Switch.
The first computer networks were realized among the companies’ own products. for example
IBM operating systems using IBM network devices
they could.
The OSI model allowed manufacturers to produce interoperable network devices. She
model on a computer, other over network media (media)
the transfer to the application on the computer.