Networks are further classified into various
types depending on their size, expanse, security, purpose and many other
parameters. While covering all these classifications is beyond the scope of the
CCNA exam, there are two important network classifications that you need to
know about for the exam. In fact a large part of the CCNA exam revolves around
these two types of networks:
·
Local Area Network (LAN) – This is
a term used to describe a network covering a limited geographical area such as
a floor, building or a campus. LAN usually has a high data-transfer rate. The
Ethernet standard is the most commonly used technology in LANs. Ethernet is so
common that it is almost synonymous with LAN today. As of late, wireless
technology is also becoming increasingly common for a local LAN. Both these
standards are covered in depth further in the book.
·
Wide Area Network (WAN) – This is a term
used to describe a network covering a large geographical area such as a
multiple cities, a country or even across the world. They are used to connect
LANs across the area they cover. A typical example would be the LANs at various
offices of a company connected by WAN. Various technology standards used in WAN
will be covered later in the book.
Internetworking Models
As the
importance of computers grew, vendors recognized the need for networking them.
They created various protocols whose specifications were not made public. Hence
each vendor had different ways of networking computers and these ways were not
compatible to each other. This means that computers of one vendor could not be
networked with another vendor’s computers. Slowly these specifications were
made public and some inter-vendor compatibility was created but this still
represented too many complications. In 1977 the International Organization for
Standardization (ISO) started working on an open standard networking model that
all vendors would support to promote inter-operability. This standard was
published in 1984 and was known as the Open Systems Interconnection (OSI).
During the same time period (1973 to 1985) another effort by the Defense
Advanced Research Projects Agency (DAPRA) was underway to create an open
standard network model. This network model came to be known as the TCP/IP
Model. By 1985, the TCP/IP model started gaining more prominence and support
from vendors and eventually replaced the OSI model.
This section starts by discussing the OSI
Reference model in some depth before moving into a deep discussion on the
TCP/IP model and its protocols