Cold War, and the main purpose of the project was to
build a telecommunications network that would be able
to withstand a nuclear attack and still be able to function
if any of the devices making up the network were
destroyed or disabled.
Much like the OSI model, the TCP/IP reference model
uses a layered approach (see Figure 16-2). Each layer
provides the functionality and features specified in the
reference model and serves the layer above it.
Figure 16-2 TCP/IP Reference Model Layers
The network access layer in the TCP/IP model
corresponds to the physical and data link layers in the
OSI model, and it provides the same services to the layer
above. It deals with moving data packets between the
Internet layer interfaces of two devices connected on the
same link. It specifies the physical characteristics of
serial lines, Ethernet, and wireless links, such as voltage
levels, data transmission rates, maximum transmission
distance, and physical connectors. The network layer
defines how data is formatted for transmission on the
physical link, how the data packet is received from the
Internet layer for transmission by adding a header and
footer, how the data frames are transmitted over the
physical medium, how access to the network is