Syed Zeeshan Nasir
Department of computer science FUUAST, Islamabad
In 1983, the International Organization for
Standardization (ISO) and the International
Telegraph and Telephone Consultative
Committee (CCITT) merged documents and developed the OSI model, which is based on a specific hierarchy where each layer builds on the output of each adjacent layer.
The OSI model is a protocol stack where the lower layers deal primarily with hardware, and the upper layers deal primarily with software. The OSI model’s seven layers are designed so that control is passed down from layer to layer. The seven layers of the
OSI model are shown:
Application support such as
File Transfer Protocol (FTP),
Hypertext Transfer Protocol
Presentation Encryption, Server Message
Block (SMB), American
Standard Code for Information Interchange
(ASCII), and formatting
Data flow control, startup, shutdown, and error detection/
communications, UDP and
Routing and routable protocols such as IP and
Open Shortest Path
First (OSPF). Path control and best effort at delivery
Network interface cards,
Media Access Control (MAC) addresses, framing, formatting, and organizing data
Transmission media such as twisted-pair cabling, wireless systems, and fiber-optic cable
1.2-Functions of OSI Model:
The OSI model functions as follows:
1. Information is introduced into the application layer and passed down until it ends up at the physical layer.
2. Next, it is transmitted over the physical medium (i.e., wire, coax, or wireless) and sent to the target device.
3. Once at the target device, it proceeds back up the stack to the application layer.
1.3-Explanation of Layers:
The Application Layer:
Layer 7 is known as the application layer.