CCENT Cisco Certified Entry Networking Technician Study Guide: (ICND1 Exam 640-822), 2nd Edition

TCP/IP and the DoD Model

The DoD model is basically a condensed version of the OSI model—it's composed of four, instead of seven, layers:

• Process/Application layer
• Host-to-Host layer
• Internet layer
• Network Access layer

Figure 2.1 compares 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.

FIGURE 2.1 The DoD and OSI models

When the different protocols in the IP stack are discussed, the layers of the OSI and DoD models are interchangeable. In ...