Overview of TCP/IP model

- The Transmission Control Protocol Internet Protocol suite better known as TCPIP, was designed and implemented by the US Department of Defense, to ensure and preserve data integrity as well as maintain communication in the event of catastrophic war. If designed and implemented correctly, a TCPIP network can be secure, dependable and resilient. I'll begin by exploring the DOD's version of TCPIP then I'll compare that version and it's protocols with the OSI reference model that we discussed earlier.

The DOD Model is basically a condensed version of the OSI model that's comprised of four instead of seven layers. The four layers are Process/Application, Transport, Internet and Link. This graphic offers a comparison of the DoD Model and the OSI reference Model. As you can see the two are similar in concept, but each has a different number of layers. With different names. I'll focus on a few of the most important applications found in the season objectives. First, it's worth noting that CISCO sometimes uses multiple names for the same layer.

The transport layer is also referred to as Host-to-Host, while Network Access and Link are used to the describe the Physical and Data Link layers. A vast array of protocols join forces in the DoD Process/Application layer. These processes combine the OSI Model's top three layers. Application, Presentation and Session. In short, the Process/Application layer defines protocols for node-to-node application communication and controls user interface specifications. The DoD Transport layer parallels the functions of the OSI's Transport layer.

Define protocols for setting up the levels of transmission service for applications. It tackles issues like creating reliable end-to-end communication and ensuring error-free delivery of data. It handles Packet Sequencing and maintains data integrity. The internet layer corresponds to the OSI's network layer, designating the protocols relating to the logical transmission of packets over the entire network. It takes care of host addressing by giving them an IP address and handles the routing of packets among multiple networks.

At the bottom of the DoD Model, the Network Access layer or Link layer implements the data exchange between the host and the network. The equivalent of the Data Link and Physical layers of the OSI Model, the Network Access layer oversees hardware addressing and defines protocols for the physical transmission of data. TCPIP became so popular, because there are no set Physical layer specifications. So it can run on any existing or future physical network.