OSI Model

Open Systems Interconnection Model

• Developed by ISO to form a standard model for computer networks

Layers of OSI Model

It has 7 layers, which are as follows from top to bottom:

Application Layer

• End User Layer, where applications access the network services
• e.g: HTTP, FTP, IRC, SSH, DNS

Presentation Layer

• Where the data format specification and encryption are performed
• e.g: SSL, SSH, IMAP, FTP, MPEG, JPEG

Session Layer

• Maintains connections and controls ports
• e.g: APIs, Sockets, WinSock

Transport Layer

• E2E data transmission
• e.g: TCP, UDP

Network Layer

• Physical path of data
• e.g: IP, ICMP, IPSec, IGMP

Data Link Layer

• Defines format of data in the network
• e.g: Ethernet, PPP, Switch, Bridge

Physical Layer

• Transmits raw bit stream over the physical medium
• e.g: Coax, Fiber, Wireless, Hubs, Repeaters