CCNA - OSI - TCP/IP

TL;DR

OSI is a 7-layer reference model that helps you understand and troubleshoot networking step by step.

TCP/IP is the practical model used on real networks and the internet; it has fewer layers because it groups some OSI layers together.

Layer	Name	Description
7	Application	The application (i.e. Web browsers, email programs, etc…)
6	Presentation	Establish data formatting and data translation
5	Session	Creates the setup, controls the connection and ends the teardown between devices
4	Transport	The transport layer provides the functional and procedural means of transferring variable-length data sequences from a source host to a destination host from one application to another across a network while maintaining the quality-of-service functions. Transport protocols may be connection-oriented or connectionless.
3	Network	Transfer packets from one node to another connected in “different networks”
2	Data Link	Node-to-node data transfer, defines the protocol to establish/terminate a connection between two physically connected devices. Defines protocol for flow control between them
1	Physical	Transmits raw data between a device and a transmission medium

Layer	Name	Description
5	Application	The services and protocols apps use (i.e. web traffic)
4	Transport	Protocols like TCP and UDP, plus port numbers
3	Network	IP Addresses & routing between networks
2	Data Link	MAC Addresses & local network communication
1	Physical	Cables, signals, network cards, electrical or wireless transmission

Data link and Physical layers can be merged into the Network Interface layer in the TCP/IP 4 layers model.