OSI MODEL
The term OSI stands for Open Systems Interconnection and the Model states the process by which data from one computer system moves through a physical medium to another computer system. This model consists of seven layers which all perform a specific function so as to ensure data is transmitted successfully.
OSI MODEL
The term OSI stands for Open Systems Interconnection and the Model states the process by which data from one computer system moves through a physical medium to another computer system. This model consists of seven layers which all perform a specific function so as to ensure data is transmitted successfully.
1.Physical layer.
This is the lowest layer of the OSI model. It deals with the physical connection from one device to another. This layer converts data in form of bits and sends it to the data link layer.
Functions of physical layer
1. Bit synchronization
Bits are synchronized by a clock which controls data sender and receiver.
2 . Bit rate control.
It controls the rate at which bits are transmitted.
3.Pysical topology.
It describes how nodes are arranged in a network.
Physical layer topology devices include modems, repeaters, cables and hubs.
2. Data link layer
This layer of the OSI model deals with the transmission of data from one node to another. It also ensures that data transmission between one node and another is free from errors.
This layer is further divided into two sub-layers.
a) Logical link control.
It deals with the sending of packets to the network layer and also ensures the flow is controlled.
b) Media Access control layer.
This layer deals with packet transfer through the network.
Functions of the data-link include the following.
a) Framing
It created way for a sender to transmit data in form of bits to the receiver.
b) Error control
Ensures there is no error during the transmission of data.
c) Access control
This layer ensures that when a medium is requested by many devices to access certain data, it determines who has control first.
Devices in data link layer include bridge and switch.
3.Network layer
Deals with data transmission between one network host and another which is in a different location. This layer also deals with packet routing by determining the shortest route for transmission of data.
Functions of Network layer.
a) Routing
Determines the best suitable route for data.
b) Logical Addressing.
It deals with IP address to ensure that devices in a network are identified.
Devices in this layer include routers.
4. Transport layer.
This layer deals with the delivery of data to the receiver. This layer converts data into smaller forms known as segments.
Functions of transport layer.
1. Service point addressing.
It issues an address to each program at the time when a computer tries to run many programs at the same time.
2. Connection control.
3. Flow control
This layer ensures smooth flow of data between the sender and the receiver.
4. Error control.
It ensures that the receiver gets the data without any error.
The following three layers below are classified into the application layer. They are referred to as the upper layers of the OSI Model.
5. Session layer
This layer deals with establishing connection, session maintenance and authentication to access a certain website or application.
Functions of session layer.
a) Establishment and maintenance of sessions.
b) Synchronization
Data synchronization ensures that data received is error free.
6. Presentation layer.
This layer is also known as the translation layer.
It manipulates data from the application layer into the correct format before transmission through a network.
Functions of the session layer.
1. Translation
2. Compression.
Bits being transmitted through a certain network are reduced to a certain number.
3. Encryption/decryption.
This deals with data translation from a certain form to another.
7. Application layer.
This layer deals with issues such as allocation of resource and transparency of network. This layer acts as a window for application services. Examples of applications are Skype messenger and browsers.
This layer is also known as desktop layer.
Functions of application layer.
1.Mail services.
2.Directory services.
3.File transfer access and management.
SUBSCRIBE TO OUR YOUTUBE CHANNEL BELOW TO WATCH MORE VIDEOS
