It contains applications that facilitate network
Such as Hypertext Transfer Protocol (HTTP) for browsing
the World Wide Web transferring files on net-works and over
At the Application layer, the data still resembles something
that people can read and interpret.
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.
It is responsible for establishing, synchronizing,
maintaining, and then terminating the sessions between
It also handles error detection and notification.
This layer is responsible for resending any packets that do
not receive an acknowledgment from the destination
It's also responsible for any problems that are associated
with fragmentation of packets.
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
The Network layer contains many protocols that facilitate
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
The Data Link layer is subdivided into two other layers:
Logical Link Control (LLC)
Media Access Control (MAC)
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.