OSI Model

Open Systems Interconnection (OSI)
https://www.imperva.com/learn/application-security/osi-model/

layer	name	desc
7	application	end-user software, Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS)
6	presentation	encode, encrypt, and compress data
5	session	creates communication channels/session, controls ports
4	transport	data transmission segments, flow and error control, TCP/UDP
3	network	breaks up segments into network packets when sending and reassemble on receive, routing
2	data link	data format over network, establishes and terminates a connection between two physically-connected nodes on a network. It breaks up packets into frames and sends them from source to destination. This layer is composed of two parts—Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.
1	physical	physical cable or wireless connection between network nodes.