OSI LAYERS

Application Layer

It contains applications that facilitate network communication.

Such as Hypertext Transfer Protocol (HTTP) for browsing the World Wide Web transferring files on net-works and over the Web.

At the Application layer, the data still resembles something that people can read and interpret.

Presentation Layer

At the Presentation layer (Layer 6) data is first converted into a form that can be sent over a network.

At this layer data is compressed and decompressed and encrypted or decrypted.

Session Layer

It is responsible for establishing, synchronizing, maintaining, and then terminating the sessions between computers.

It also handles error detection and notification.

Transport Layer

This layer is responsible for resending any packets that do not receive an acknowledgment from the destination address.

It's also responsible for any problems that are associated with fragmentation of packets.

Network Layer

The Network layer (Layer 3) is responsible for providing the mechanism by which data can be moved from computer to computer or from network to network.

The Network layer does not actually move the data; instead it provides the addressing information and route discovery that are necessary to move the data to the appropriate location.

The Network layer contains many protocols that facilitate these services.

Internet Protocol (IP), Internet Control Message Protocol (ICMP), Internet Group Management Protocol (IGMP), Address Resolution Protocol (ARP).

Data Link Layer

The Data Link layer (Layer 2) is responsible for sending data to the Physical layer so that it can be put onto the "wire" or network media.

The Data Link layer is subdivided into two other layers:Logical Link Control (LLC) Media Access Control (MAC)

Physical Layer

The Physical layer (Layer 1) defines the physical characteristics of the network such as the type of cable that must be used as well as the voltage that will be used to transmit data through the network.

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