Understand Layer of Osi Model and their function.
Understand Layer of Osi Model and their function.
Layer 7 – Application layer
This is the closest layer to the end user. It provides the interface between the applications we use and the underlying layers. But notice that the programs you are using (like a web browser – IE, Firefox or Opera…) do not belong to Application layer. Telnet, FTP, email client (SMTP), HyperText Transfer Protocol (HTTP) are examples of Application layer.
Layer 6 – Presentation layer
This layer ensures the presentation of data, that the communications passing through are in the appropriate form for the recipient. In general, it acts as a translator of the network. For example, you want to send an email and the Presentation will format your data into email format. Or you want to send photos to your friend, the Presentation layer will format your data into GIF, JPG or PNG… format.
Layer 5 – Session layer
Layer 5 establishes, maintains and ends communication with the receiving device.
Layer 4 – Transport layer
This layer maintains flow control of data and provides for error checking and recovery of data between the devices. The most common example of Transport layer is Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
Layer 3 – Network layer
This layer provides logical addresses which routers will use to determine the path to the destination. In most cases, the logic addresses here means the IP addresses (including source & destination IP addresses).
Layer 2 – Data Link Layer
The Data Link layer formats the message into a data frame, and adds a header containing the hardware destination and source address to it. This header is responsible for finding the next destination device on a local network.
The MAC sublayer carries the physical address of each device on the network. This address is more commonly called a device’s MAC address. MAC address is a 48 bits address which is burned into the NIC card on the device by its manufacturer.
Layer 1 – Physical layer
The Physical Layer defines the physical characteristics of the network such as connections, voltage levels and timing.
To help you remember the functions of each layer more easily, I created a fun story in which Henry (English) wants to send a document to Charles (French) to demonstrate how the OSI model works.
Example in daily life:
TIPS TO REMEMBER THE LAYER !!
- All - APPLICATION
- People- PRESENTATION
- Seem- SESSION
- To - TRANSPORT
- Need - NETWORK
- Data- DATA LINK
- Processing- PHYSICAL
- All - APPLICATION
- People- PRESENTATION
- Seem- SESSION
- To - TRANSPORT
- Need - NETWORK
- Data- DATA LINK
- Processing- PHYSICAL
OR
- Please - PHYSICAL
- Do- DATA LINK
- Not - NETWORK LAYER
- Throw- TRANSPORT
- Sausage- SESSION
- Pizza- PRESENTATION
- Away- APPLICATION
- Please - PHYSICAL
- Do- DATA LINK
- Not - NETWORK LAYER
- Throw- TRANSPORT
- Sausage- SESSION
- Pizza- PRESENTATION
- Away- APPLICATION
When the information goes down through layers (from top to bottom), a header is added to it. This is called encapsulation because it is like wrapping an object in a capsule. Each header can be understood only by the corresponding layer at the receiving side. Other layers only see that layer’s header as a part of data.
At the receiving side, corresponding header is stripped off in the same layer
it was attached.
ADVANTAGES of OSI MODEL
Reduces complexity:
It breaks network communication into smaller, simpler parts. It divides the network communication process into smaller and simpler components, thus aiding component development, design, and troubleshooting.
It breaks network communication into smaller, simpler parts. It divides the network communication process into smaller and simpler components, thus aiding component development, design, and troubleshooting.
Standardizes interfaces:
It standardizes network components to allow multiple vendor development and support.
It standardizes network components to allow multiple vendor development and support.
Facilitates modular engineering:
It allows different types of network hardware and software to communicate with each other.
It allows different types of network hardware and software to communicate with each other.
Interoperability between Vendors:
It allows multiple-vendor development through standardization of network components. Defines the process for connecting two layers together, promoting interoperability between vendors It Allows vendors to compartmentalize their design efforts to fit a modular design, which eases implementations and simplifies troubleshooting
It allows multiple-vendor development through standardization of network components. Defines the process for connecting two layers together, promoting interoperability between vendors It Allows vendors to compartmentalize their design efforts to fit a modular design, which eases implementations and simplifies troubleshooting
DISADVANTAGES of OSI MODEL
- OSI is complex and costly
- Not so widespread as TCP/ IP
- OSI is complex and costly
- Not so widespread as TCP/ IP
- The OSI (Open System Interconnection) Model breaks the various aspects of a computer network into seven distinct layers. Each successive layer envelops the layer beneath it, hiding its details from the levels above.
What a differences between OSI MODEL and TCP/IP??
- The application layer in TCP/IP handles the responsibilities of layers 5, 6 and 7 in the OSI model.
- The transport layer in TCP/IP does not always guarantee reliable delivery of packets at the transport layer, while the OSI model does. TCP/IP also offers an option called UDP that does not guarantee reliable packet delivery.
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