Several network reference models have been developed
through the years, some of them proprietary and some
open. Two reference models stand out from the crowd
for their importance and longevity: the OSI model and
the TCP/IP reference model.
The OSI Model
In the late 1970s, as computing devices became more and
more popular, a need to connect them in a manner in
which they would be able to exchange data between them
arose. The old sneakernet—which involved physically
copying data that needed to be transferred between
devices on a floppy disk and delivering it on foot—was no
longer appropriate for the amounts of data that needed
to be exchanged. Disparate proprietary solutions such as
System Network Architecture (SNA) from IBM and
DECnet from Digital Equipment Corporation (DEC)
existed for this purpose, but there was a need to have a
standard, interoperable, and common way to do
networking. The International Organization for
Standardization (ISO) took on this challenge and came
up with the Open Systems Interconnection (OSI) model.
Although it has not been implemented in production
systems, the OSI model is still extensively used especially
from an educational perspective. The simpler TCP/IP
(Transport Control Protocol/Internet Protocol) model
has had much more success in real life and is covered in
more detail later in this chapter.
The main idea with developing networking models based
on different layers that interact with each other was
inspired by the computer science mantra of splitting a
difficult problem into smaller more manageable
problems. Following this philosophy, the OSI model
splits the data transmission processes needed to transfer
data between two or more devices into seven layers. An
advantage with a layered approach is that there can be
different vendors at different layers implementing the
specific functionality required by each layer. There are