TUTORIAL
2 - OSI MODEL
OSI model is a reference tool for
understanding data communication between any network systems. It consists of seven layers where one layer performs specific functions
to support the layer above it.
LEVEL
1- PHYSICAL LAYER
· Describes
the electrical or optical signals used for communication. It
is responsible for movement of bits from one node to the next. It
is concerned with physical characteristics of electric or optical signalling
techniques , representation of bits, data rate (number of bits sent per second
and duration of the bit), synchronization of bit, line configuration(
connection of devices to the media), physical topology and transmission
mode(simplex, half-duplex, full duplex).
LEVEL
2- DATA LINK LAYER
· Transforms
physical layer into a link making it error free to the layers above. It
is responsible for moving frames i.e packets with address information. It
is concerned with framing which divide bits into data units knows as frames,
physical addressing of the frames, flow control of the data, error control
which adds reliability to the link, and access control which determines which
device has control over the link.
LEVEL
3- NETWORK LAYER
· Source
to destination delivery of packets (small chunks of broken data sent over a
computer network) ensuring that it arrives at its destination intact. It
is responsible for Logical addressing adding a header to the packet received
from the above layer and Routing which sends the packet to its final
destination.
LEVEL
4- TRANSPORT LAYER
· Responsible
for process to process delivery of the entire message ensuring that it arrives
at the destination intact and in order. Other
responsibilities include error control, flow control, connection control
between devices and terminating it after data is transferred, segmentation and
reassembly where a message is divided into segments that contain sequence
numbers which allows for the message to be reassembled upon destination arrival
and service point addressing also known as port address.
LEVEL
5- SESSION LAYER
· It
is responsible for developing, maintaining and synchronizing interaction
between communication systems. It
is also its responsibility to allow systems to dialog allowing processors to
communicate using the same transmission mode and synchronization of the data.
LEVEL
6- PRESENTATION LAYER
· This
layer is responsible for the translation of the information to bits prior
transmission, compression of data to reduce the number of bits contained, and
encryption which transforms the original information into a different form
before sending it forward.
LEVEL
7-APPLICATION LAYER
· Allows
user access to the network. It
offers mail services, directory services that provide distributed database
source and access to global information, file transfer, access and management,
and network virtual terminal that allows a user to log onto a remote host.
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REFERENCE
LIST
Simoneau,P.2009.The OSI model:
Understanding the seven layers of computer networks(PDF).:Global Knowledge
Training. Available: http://faculty.spokanefalls.edu/Rudlock/files/WP_Simoneau_OSIModel.pdf (Accessed 04
September 2015)
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