DoD Four-Layer Model
The Department of Defense Four-Layer Model was developed in the 1970s for the
DARPA Internetwork Project that eventually grew into the Internet.
The core Internet protocols adhere to this model, although the OSI
Seven Layer Model is justly preferred for new designs.
The four layers in the DoD model, from bottom to top, are:
The Network Access Layer is responsible for delivering data
over the particular hardware media in use. Different protocols are selected
from this layer, depending on the type of physical network.
The Internet Layer is responsible for delivering data across
a series of different physical networks that interconnect a source
and destination machine. Routing protocols are most closely associated
with this layer, as is the IP Protocol, the Internet's fundamental
protocol.
The Host-to-Host Layer handles connection rendezvous,
flow control, retransmission of lost data, and
other generic data flow management. The mutually exclusive
TCP and UDP protocols are this layer's most important members.
The Process Layer contains protocols that implement user-level
functions, such as mail delivery, file transfer and remote login.
