The TCP/IP Model is the implemented network protocol suite of the internet, the OSI Model is now considered a theoretical model because it was never caught on like TCP/IP but it has been a very influential model. Cisco uses both the OSI and the TCP/IP models to talk about how data is separated into pieces which are turned into smaller packages.
This process is called encapsulation which happens from Layer 7 down to Layer 1. The encapsulated packets or packages travel across the network or the internet and are rebuilt – decapsulation) at the receiving host end. Decapsulation happens from the bottom up, Layer 1 to Layer 7
As data is built into packets or packages it is done in layers. By separating the networking process into layers developers and engineers are able to isolate the necessary functions for their products and not concern themselves with the entire networking architecture. In this way, a layered approach and the rules and protocols recommended by each layer, promote hardware compatibility, easier software development, and competition. By clearly separating the role of each layer networkers are able to easily troubleshoot network failures. It is common for network technicians to identify a layer 1 issue as an unplugged network cable. Similarly a computer which can ping an ip address but is unable to ping a domain name is operating fine at layer 3 but is having an issue at layer 7. See my video tutorials below for an explanation of network layer characteristics.