OSI & TCP/IP models Defination and Types

What is OSI Model?

OSI (Open Systems Interconnection) model was created by the International Organization for Standardization (ISO), an international standard-setting body. It was designed to be a reference model for describing the functions of a communication system. It has seven layers, with each layer describing a different function of data traveling through a network.

The OSI model was originally conceived as a standard architecture for building network systems and indeed, many popular network technologies today reflect the layered design of OSI.

Layers are generally numbered from the last one, that is, the physical layer is considered as the first layer. It is good to learn these levels, because there are several questions in the CNNA exams about them. Most people learn this thing "Please do not waste the sausage pizza away".

If you want to know from where it is being used.

They are most commonly used by vendors. They enable them to implement some functionality into a networking device, which then enables easier interoperability with devices from other vendors.

The OSI model is the primary architectural model for networks. It describes how data and network information are communicated from an application on one computer through the network media to an application on another computer. The OSI reference model breaks this approach into layers. 

Here is a brief description of each of these layers.

Physical – defines how to move bits from one device to another. It details how cables, connectors and network interface cards are going to work and how to send and receive bits.

Data Link – encapsulates a packet in a frame. A frame contains a header and a trailer that enable devices to communicate. A header, most commonly, contains a source and a destination MAC address. A trailer contains the Frame Check Sequence field, which is used to detect transmission errors.
The data link layer has two sub layers:

1.    Logical Link Control – used for flow control and error detection
2.    Media Access Control – used for hardware addressing and controlling the access method

Network - Determining device addressing, routing, and posing. To identify a network host using a device (logical) addressing (such as its IP address).
 Transport - Large parts of the data received from the upper protocol are redeemed. Used for connecting between two computers and finished flow control and data recovery
 Session - Determines how a session between two systems is installed and finished.
 Presentation - Defining the Data Format This layer is compressed and encrypted.
 Applications - The closest to the Layer user. This network application will be able to communicate with other network applications

Photo of OSI Model Stracture-CCNA Tutorial

CP/IP mod

The TCP/IP model was created in the 1970s by the Defense Advance Research Project Agency (DARPA). Like the OSI model, it describes general guidelines for designing and implementing computer protocols.

TCP IP Model-CCNA-Tutorials.png

That's all. You can also find more on cisco site. They also provide sufficient knowledge on about it on their reading materials.