By KailinAchesonThe first two parts of this blog, Part 1 and Part 2, covered the seven layers in the Open Systems Interconnection model. This installment will focus on the four layers of Transmission Control Protocol/Internet Protocol (TCP/IP). It will also compare the TCP/IP model to the OSI model.
The OSI model and TCP/IP are related in that they both use layered reference models to show how data and information are transferred between devices. They are however different in that the TCP/IP has four layers (Application Transport, Internet and Network Access), while the OSI model has seven layers. These layers are Physical, Data Link Network, Transport and Transport as well as Presentation, Presentation, and Application. The following graphic illustrates how the layers relate when compared side-by-side:

As you can see, there are fewer layers in the TCP/IP model, which overlap with the OSI model in some cases. Unlike the OSI model, which focuses on certain layers and is structured with these layers as the main focus, the TCP/IP model is structured with architectural principles being the primary focus.
Part I (which includes the Physical, Data Link and Transport layers) and part II (which includes the Session and Presentation layers) will refresh your knowledge about the OSI model’s layers. I won’t go into detail about each layer. What you will see below is a summary of each layer to give you an idea of the basics.
The Application Layer
TCP/IP Application layer (also known as the Process layer) is the top layer closest to you, your user. It is responsible for delivering data to the specific applications on the computer for which they were intended. The Application layer is responsible for data compression and encryption, as well as the creation, maintenance and termination of sessions as required. File Transfer Protocol, Simple Mail Transfer Protocol, SMTP, Domain Name System (DNS), Telnet and Hypertext Transfer Protocol are some of the most common protocols that operate at TCP/IP Application Layer. The Application layer of TCP/IP corresponds to Layer 7 (Layer 7), 6 (Layer 6), and 5 (Layer 5) in the OSI model.
The Transport Layer
TCP/IP Transport layer (also known as the Host to-Host layer) is responsible for data delivery between the Internet layer & the Application layer, flow control and congestion control, data segmentation, and error control and recovery. TCP/IP Transport layer is home to two common protocols: Transmission Control Protocol (TCP), and User Datagram Protocol [UDP]. Network devices, or gateways, are the devices that operate at the Transport Layer. The Transport layer of TCP/IP corresponds to Layer 4 of the OSI model.
The Internet Layer
TCP/IP Internet layer (also known as the Internetwork Layer) is responsible for defining logical addresses and delivering packets. Internet Protocol is the main protocol at this layer. It uses the source and destination addresses to facilitate data movement between the Network Access layer (also known as the Internetwork layer) and the Transport layer (data flows from one node to the next in a path that leads to the destination). Two other protocols that are commonly used at the TCP/IP Internet Layer are IPv4 and IPv6. Routers are the devices that operate at the Internet layer. The Internet layer of TCP/IP corresponds to Layer 3 of the OSI model.
The Network Access Layer
The TCP/IP Network access layer, also known as the Link layer or Network Interface layers, determines how data will be delivered over a physical network and what protocols are appropriate. This layer also handles error discrepancy and arbitration.