Presentation (Layer 6)
This layer provides independence from differences in data representation (e.g.,
) by translating from application to
network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept.
This layer formats and encrypts data to be sent across a
, providing freedom from
problems. It is sometimes
called the syntax layer.
Session (Layer 5)
This layer establishes, manages and terminates connections between
. The session layer sets up, coordinates, and
terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection
Transport (Layer 4)
This layer provides transparent transfer of data between end systems, or
, and is responsible for end-to-end error recovery
. It ensures complete data transfer.
Network (Layer 3)
This layer provides
technologies, creating logical paths, known as
, for transmitting data
to node. Routing and forwarding are functions of this layer, as well as
control and packet sequencing.
Data Link (Layer 2)
At this layer, data packets are
and decoded into bits. It furnishes
knowledge and management and
handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers:
The Media Access Control (
) layer and the
Logical Link Control
(LLC) layer. The MAC sub layer controls how a computer
on the network gains access to the data and permission to transmit it. The LLC layer controls frame
, flow control
and error checking.
Physical (Layer 1)
This layer conveys the bit stream - electrical impulse, light or radio signal -- through the
at the electrical and mechanical
level. It provides the
means of sending and receiving data on a carrier, including defining cables, cards and physical
with physical layer components.
Analog Network Signaling
An analog signal is best compared to a wave. It has similar properties to an ocean wave, and can be described using three
specific characteristics: amplitude, frequency, and wavelength.
To use the ocean wave analogy an analog signal's amplitude is like the height of a wave rolling in onto the beach. The frequency
of an analog signal can be compared to how fast the waves roll in. Wavelength can be compared to the distance between one
wave and the next wave. Wavelength is measured as the distance between the peak of one wave and the next.