Open Systems Interconnection
OSI model is the layer approach to design, develop and
implement network. OSI provides following advantages: -
- Designing of network will be standard base.
- Development of new technology will be faster.
- Devices from multiple vendors can communicate with each
other.
- Implementation and troubleshooting of network will be easy.
1. Application Layer: -
Application layer accepts data and
forward into the protocol stack. It creates user interface between application software and
protocol stack.
2. Presentation Layer: -
This layer decides presentation format of the data. It also able to
performs other function like compression/decompression and
encryption/decryption.
3. Session Layer: -
This layer initiate, maintain and terminate sessions between different
applications. Due to this layer multiple application software can be executed
at the same time.
4. Transport Layer: -
Transport layer is responsible for connection oriented and connection
less communication. Transport layer also performs other functions like
Error checking
- Flow Control
- Buffering
- Windowing
- Multiplexing
- Sequencing
- Positive Acknowledgement
- Response
5. Network Layer
This layer performs function like logical addressing and path
determination. Each networking device has a physical address that is MAC
address. But logical addressing is easier to communicate on large size network.
Logical addressing defines network address and
host address. This type of addressing is used to simplify implementation of
large network. Some examples of logical addressing are: - IP addresses, IPX
addresses etc.
6. Data Link Layer
The functions of Data Link layer are divided into two sub layers
- Logical Link Control
- Media Access Control
Logical Link Control defines the encapsulation that will be used by the
NIC to delivered data to destination. Some examples of Logical Link Control are
ARPA (Ethernet), 802.11 wi-fi.
Media Access Control defines methods to access the shared media and
establish the identity with the help of MAC address. Some examples of Media
Access Control are CSMA/CD, Token Passing.
7. Physical Layer
Physical Layer is
responsible to communicate bits over the media this layer deals with the
standard defined for media and signals. This layer may also perform modulation
and demodulation as required. 
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