OSI MODEL

OSCI Layer
Physical Layer 1:
contains the infrastructure that makes communication on networks possible.
It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating physical links between network devices.

Data Link Layer 2:
The Data Link Layer allows nodes to communicate with each other within a local area network. The foundations of line discipline, flow control, and error control are established in this layer.

Network Layer 3:
The Network Layer allows nodes to connect to the Internet and send information across different networks.

Transport Layer 4:
The Transport Layer provides end-to-end transmission of a message by segmenting a message into multiple data packets; the layer supports connection-oriented and connectionless communication.

Session Layer 5:
The Session Layer initiates, maintains, and terminates connections between two end-user applications. It responds to requests from the presentation layer and issues requests to the transport layer.

Presentation Layer 6:
The Presentation Layer formats and encrypts data.

Application Layer 7:
The Application Layer owns the services and functions that end-user applications need to work. It does not include the applications themselves.

OSI Layer Ports
Application Layer 7
HTTP (80), HTTP (443), FTP (20), SFTP (22), SSH (22), SMTP (25), POP3 (110), DNS (53), SNMP (161), DHCP (67, 68), NTP (123/udp), LDAP (389)
Presentation Layer 6
SSL (443), TLS (443)
Transport Layer 4
TPC, UDP
Network Layer 3
IP, ICMP, IPSEC