1.5 NETWORK CLASSIFICATION
There are mainly three types of networks:
1) LAN (Local Area Network)
2) MAN (Metropolitan Area Network)
3) WAN (Wide Area Network)
1.5.1 Local Area Network (LAN)
LAN (Figure 1.10) is a group of computers located in the same room, on the same
floor or in the same building that are connected to form a single network as to share
resources such as disk drives, printers, data, CPU, fax/modem, applications etc.
LAN is generally limited to specific geographical area less than 2 Km., supporting
high speed networks. A wide variety of LANs have been built and installed, but a few
types have more recently become dominant. The most widely used LAN system is the
Ethernet system based on the bus topology.
Intermediate nodes (i.e., repeaters, bridges and switches discussed in section 1.7)
allow to be connected together to from larger LANs. A LAN may also be connected to
another LAN or to WANs and MANs using a ―Router‖ device.
In general, there are five components of a LAN:
2) Network Communication Devices i.e., devices such as hubs, routers, switches etc.
that are used for network connectivity.
3) Network Interface Cards (NICs) for each network device required to access the
network. It is the interface between the machine and the physical network.
4) Cable as a physical transmission medium. However, present day LAN may not
require the physical transmission media. It may be a Wireless LAN. (Please refer
to further readings for more details on wireless LANs)
5) Network Operating System –software applications required to control the use of
network operation and administration.
Characteristics of LAN
It connects computers in a single building, block or campus, i.e. they work in a
restricted geographical area.
LANs are private networks, not subject to tariffs or other regulatory controls. For
the Wireless LANs there are additional regulations in several countries.
LANs operate at relatively high speed when compared to the typical WAN (.2 to
100 MB /sec).
There are different types of Media Access Control methods in a LAN, the
prominent ones are Bus based Ethernet, Token ring.
Advantages of LAN
It allows sharing of expensive resources such as Laser printers, software and mass
storage devices among a number of computers.
LAN allows for high-speed exchange of essential information.
It contributes to increased productivity. A LAN installation should be studied
closely in the context of its proposed contribution to the long range interest of the
organization.
Disadvantage of LAN
Some type of security system must be implemented if it is important to protect
confidential data. The security may be further low if it is a wireless LAN.
1.5.2 Metropolitan Area Network (MAN)
Metropolitan area networks, or MANs, are large computer network that spans a
metropolitan area or campus. Its geographic scope falls between a WAN and LAN.
They typically use wireless infrastructure or Optical fiber connections to link their
sites.
A MAN is optimized for a larger geographical area than a LAN, ranging from several
blocks of buildings to entire cities. MANs can also depend on communications
channels of moderate-to-high data rates. A MAN might be owned and operated by a
single organization, but it usually will be used by many individuals and organizations.
MANs might also be owned and operated as public utilities or privately owned. They
will often provide means for internetworking of local networks. Metropolitan area
networks can span up to 50km, devices used are modem and wire/cable.
MANs provide Internet connectivity for LANs in a metropolitan region, and connect them to wider area networks like the Internet.
1) The network size falls intermediate between LAN and WAN. A MAN typically
covers an area of between 5 and 50 km diameter. Many MANs cover an area the
size of a city, although in some cases MANs may be as small as a group of
buildings or as large as the North of Scotland.
2) A MAN often acts as a high speed network to allow sharing of regional resources.
It is also frequently used to provide a shared connection to other networks using a
link to a WAN.
Characteristics of MAN
1) It generally covers towns and cities (50 kms)
2) It is developed in 1980s
3) Communication medium used for MAN are optical fiber cables, however it may
use other media too
4) Data rates adequate for distributed computing applications.
1.5.3 Wide Area Network (WAN)
Wide Area Network (Figure 1.12) is a network system connecting cities, countries or
continents, a network that uses routers and public communications links. The largest
and most well-known example of a WAN is the Internet.
WANs are used to connect LANs and other types of networks together, so that users
and computers in one location can communicate with users and computers in other
locations. Many WANs are built for one particular organization and are private.
Others, built by Internet service providers, provide connections from an organization's
LAN to the Internet. WANs are often built using leased lines. At each end of the
leased line, a router connects to the LAN on one side and a hub within the WAN on
the other. Leased lines can be very expensive. Instead of using leased lines, WANs
can also be built around public network or Internet.
Virtual Private Network (VPN): Consider a situation when you have a secure office
LAN which contains some important update of your company products. You are out
of the country for a business trip and want to see that information. What your
company needs is a VPN. A VPN may be defined as the secure way of connecting to
your private LAN (such as your company network) from a remote location using the
Internet or any other unsecure network. In such a case, the data that is to be
transmitted over the unsecure network is encrypted. In addition, VPNs have a proper
mechanism for authenticating the user.
Characteristics of WAN
1) It generally covers large distances (states, countries, continents).
2) Communication medium used are satellite, public telephone networks which are
connected by routers.
3) Routers forward packets from one to another on a route from the sender to the
receiver.
Table 1.1 compares the three technologies :
