TCP/IP model was developed by Department of Defense (DoD) in 1970s and adopted as the protocol standard for ARPANET in 1983.
TCP/IP is a practical model which is used to communicate different devices over internet.
As, this model does not contain proper documentation. So, Mostly books tell that TCP/IP model holds 5 layers and some other books tells that TCP/IP model holds 4-layers. But working of 4-layered or 5-layered TCP/IP model is same.
As we know OSI model holds 7 layers. Layers with Names of TCP/IP is explain in following diagram
Naming of TCP/IP Model
The Name of TCP/IP model is based on 2 protocols of its model. One is TCP protocol which is used at Transport layer and other is IP protocol which is used at Network layer.
As we know the OSI and TCP/IP model are same in functionality. So, the protocols, data formats, delivery of data etc. of TCP/IP layers are just same as the protocols of OSI layers.
For example, if protocols of Transport layer in OSI model are TCP and UDP then TCP/IP model also holds these two protocols for its transport layer.
As layer (5, 6, and 7) in OSI model combine to make an application layer in TCP/IP model. So, Application layer of TCP/IP holds all protocols of Layer 5, 6, 7 of OSI model.