The Department of Defence (DoD) has defined a four-layer networking model. Each layer of this model consists of a number of protocols that are collectively referred to as the TCP/IP protocol suite. The specifications for each protocol within the TCP/IP suite are defined within one or more Requests for Comments (RFC). The RFCs are submitted by various Internet users who are proposing new protocols, suggesting improvements of existing protocols, or even offering comments on the state of the network. These documents are online on various systems on the Internet, and are available to anyone.
Table 2 shows the DoD's four-layer model.

Layer	Description
Layer 4: Application Layer	The Application layer consists of application programs and serves as the windows, or network interface. It is through this window that all exchange of meaningful information occurs between communication users. Examples include Telnet and SMTP.
Layer 3: Host-to-Host Transport Layer	Provides end-to-end data delivery services. The protocols at this layer are TCP and UDP.
Layer 2: Internet Layer	Defines the datagram or frame format and handles routing data through an internetwork. Examples include IP and ICMP.
Layer 1: Network Access Layer	Defines how to access a specific network topology such as Ethernet or Token-Ring.

TABLE 2: THE DoD DATA COMMUNICATIONS MODEL

From Table 2, we see that the DoD's four-layer model don't exactly match those of the OSI model. For example, in DoD terms IP is a layer 2 protocol, whereas in OSI terms it is a layer 3 protocol.