early development of networks was disorganized in many ways.
The early 1980s saw tremendous increases in the number and size
of networks. As companies realized the advantages of using networking
technology, networks were added or expanded almost as rapidly
as new network technologies were introduced.
By the mid-1980s, these companies began to experience problems
from the rapid expansion. Just as people who do not speak the
same language have difficulty communicating with each other,
it was difficult for networks that used different specifications
and implementations to exchange information. The same problem
occurred with the companies that developed private or proprietary
networking technologies. Proprietary means that one or a small
group of companies controls all usage of the technology. Networking
technologies strictly following proprietary rules could not
communicate with technologies that followed different proprietary
To address the problem of network incompatibility, the International
Organization for Standardization (ISO) researched networking
models like Digital Equipment Corporation net (DECnet), Systems
Network Architecture (SNA), and TCP/IP in order to find a generally
applicable set of rules for all networks. Using this research,
the ISO created a network model that helps vendors create networks
that are compatible with other networks.
The Open System Interconnection (OSI) reference model released
in 1984 was the descriptive network model that the ISO created.
It provided vendors with a set of standards that ensured greater
compatibility and interoperability among various network technologies
produced by companies around the world.
The OSI reference model has become the primary model for network
communications. Although there are other models in existence,
most network vendors relate their products to the OSI reference
model. This is especially true when they want to educate users
on the use of their products. It is considered the best tool
available for teaching people about sending and receiving data
on a network.
The OSI reference model is a framework that is used to understand
how information travels throughout a network. The OSI reference
model explains how packets travel through the various layers
to another device on a network, even if the sender and destination
have different types of network media.
In the OSI reference model, there are seven numbered layers,
each of which illustrates a particular network function. Dividing
the network into seven layers provides the following advantages:
• It breaks network communication into smaller, more manageable
• It standardizes network components to allow multiple vendor
development and support.
• It allows different types of network hardware and software
to communicate with each other.
• It prevents changes in one layer from affecting other layers.
• It divides network communication into smaller parts to make
learning it easier to understand.
the OSI Model each layer has specific functions. Each layer
processes its data and passes it on to its adjacent layer. The
Functions are listed below
1. Physical Layer:
The physical layer handles the bits, connectors, voltages and
data rates i.e. it deals with the physical medium like a coaxial
cable and sends the data in forms of 0s and 1s.
2. Data Link Layer :
It is responsible for reliable data transfer of data through
the media. This layer understands the physical address(Media
Access Control Address) of the network device and helps in flow
control and error correction during data transfer.
3. Network Layer: This layer provides reliable data transfer.
It deals with the logical address or the IP(Internet Protocol)
4. Transport Layer: This layer is responsible for the transportation
issues between hosts. This layer is responsible for fault detection
and recovery of flow control.
5. Session Layer: This layer is responsible for establishing
and terminating virtual circuits for data transfer between two
6. Presentation layer: This layer is responsible for decrypting
the data and formats the data as sent by the sender. It also
negotiates data transfer syntax for the Application layer above
7. Application Layer: This layer provides network services to
the applications like email, File Transfer Protocol or remote
monitoring of device.
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