What is OSI Model

Why do we need the OSI Model?

To address the problem of networks increasing in size and in number, the International Organization for Standardization (ISO) researched many network schemes and recognized that there was a need to create a network model that would help network builders implement networks that could communicate and work together and therefore, released the OSI reference model in 1984.

Don’t Get Confused.

ISO - International Organization for Standardization

OSI - Open System Interconnection

IOS -  Internetwork Operating System

The ISO created the OSI to make the IOS more efficient.  The “ISO” acronym is correct as shown.  

To avoid confusion, some people say “International Standard Organization.”

The OSI Reference Model

Definition of Application Layer

The application layer is a layer in the Open Systems Interconnection (OSI) seven-layer model and in the TCP/IP protocol suite.

It consists of protocols that focus on process-to-process communication across an IP network and provides a firm communication interface and end-user services.

Layer 7 - The Application Layer

The application layer is the seventh layer of the OSI model and the only one that directly interacts with the end-user.

The application layer provides many services, including:

• Simple Mail Transfer Protocol
• File transfer
• Web surfing
• whatsapp
• Web chat
• Email clients
• Network data sharing
• Virtual terminals

Layer 6 - The Presentation Layer

This layer is responsible for presenting the data in the required format which may include:

The presentation layer is sometimes called the syntax layer.

• Data encryption/decryption
• Character/string conversion
• Data compression
• Graphic handling

Layer 5 - The Session Layer

This layer establishes, manages, and terminates sessions between two communicating hosts.

Example:

• Client Software

Layer 4 - The Transport Layer

This layer breaks up the data from the sending host and then reassembles it in the receiver.

It also is used to insure reliable data transport across the network.

Layer 3 - The Network Layer

Sometimes referred to as the “Cisco Layer”.

Makes “Best Path Determination” decisions based on logical addresses (usually IP addresses).

Layer 2 - The Data Link Layer

This layer provides reliable transit of data across a physical link.

Makes decisions based on physical addresses (usually MAC addresses).

Layer 1 - The Physical Layer

This is the physical media through which the data, represented as electronic signals, is sent  from the source host to the destination host.