Five Layers in the Internet Network Model and What They Do

Physical Layer

Is the physical connection between the sender and the receiver. It includes all the hardware devices (computers, modems, and hubs) and physical media (cables and satellites). This layer specifies the type of connection and the electrical signals, radio waves, or light pulses that pass through it.

Data Link Layer

Is responsible for moving a message from one computer to the next computer in the network path from the sender to the receiver. This layer has 3 functions:

1. Control the physical layer by deciding when to transmit messages over the media.
2. Format the messages by indicating where they start and end.
3. Detects and corrects any errors that have occurred during transmission.

 Network Layer

This layer performs the following functions:

1. Routing, selecting the next computer to which the message should be sent.
2. Find the address of that computer if it doesn’t already know it.

Transport Layer

It performs two functions:

1. It is responsible for linking the application layer software to the network and establishing end-to-end connections between the sender and receiver when such connections are needed.
2. It breaks long messages into several smaller messages to make them easier to transmit.
3. Detect lost messages and request that they be resent.

Application Layer

This is the application software used by the network user. With this layer the user defines what messages are sent over the network. Examples of this layer are the internet explorer and web pages.